# Contrasting phylogeographic patterns of a phytophagous insect and its host plants

Neus Marí- Mena, Carlos Lopez-Vaamonde, Horacio Naveira, Marie-Anne Auger-Rozenberg, Marta Vila

► To cite this version:

Neus Marí- Mena, Carlos Lopez-Vaamonde, Horacio Naveira, Marie-Anne Auger-Rozenberg, Marta Vila. Contrasting phylogeographic patterns of a phytophagous insect and its host plants. 15. Congress of the European Society for Evolutionary Biology (ESEB), Aug 2015, Lausanne, Switzerland., 2015, 15th Congress of the European Society for Evolutionary Biology (ESEB 2015). Congress Program & Information. hal-01603464

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Congress of the European Society
for Evolutionary Biology

Congress Program & Information

August 10 - 14, 2015

Lausanne, Switzerland

unil.ch/eseb2015

@eseb2015

#eseb15

<figure><img src="image_3.png" /></figure>

UNIL | Université de Lausanne

Département d'écologie
et évolution
# On the maintenance of sex in natural populations (53716)

Tanja Schwander.

*University of Lausanne.*

The overwhelming success of obligate sexual reproduction among eukaryotes implies that sex generates advantages that fully compensate for its inherent costs relative asexuality. Theoretical approaches have shown that the potential for sex to be advantageous increases in spatially or temporally heterogeneous environments. However, it remains unknown whether environmental heterogeneity contributes to the maintenance of sex in natural populations. I will discuss different competition experiments between sexual and asexual grassthrips in natural habitats and semi-natural mesocosm conditions through which we evaluated whether and how habitat heterogeneity can contribute to the maintenance of sexual lineages when in competition with co-occurring asexuals.

# Evolutionary advantage of sexual algal prey exposed to predation (51656)

Hanna Koch, Sophia Wagner, Lutz Becks.

*Max Planck Institute for Evolutionary Biology; Plön, Germany.*

Here, we present results from an experimental evolution study using a predator-prey system to evaluate theory for the evolution of sexual reproduction. Specifically, we tested whether sex is beneficial when populations are exposed to predation. We used an algal-rotifer system to first show that sex in an algal prey provides a direct fitness benefit by combining different beneficial mutations - for increased growth rates and grazing resistance - into one genome, whereas asexual populations suffer trade-offs in these traits. We also found that sexual prey populations evolved to higher levels of fitness over time compared to asexual prey populations. The results confirm the theory that asexual populations evolve more slowly due to clonal interference and a lack of recombination. We used the same system in a second experimental evolution study to show that the in-situ rate of sex was maintained at high levels in the presence of predation, but not in treatments without predation. Together, these results show that sex not only provides a direct fitness benefit in the presence of predation, but is also maintained which suggests an evolutionary advantage that outweighs the costs of sex within this relevant ecological context.

# Invasion of the selfers! Evolutionary ecology and the maintenance of outcrossing. (53322)
**Levi Morran.**

*Emory University.*

Outcrossing is inherently costly relative to self-fertilization.

Nonetheless, outcrossing is quite prevalent in nature. What prevents the widespread invasion and fixation of alleles permitting self-fertilization in mixed mating and obligately outcrossing populations? Here, I will discuss the results of several experimental evolution studies testing the role of parasites in preventing, slowing, and perhaps even facilitating the spread of self-fertilization in host populations. Additionally, I will discuss the potential limitations of parasites with regards to the maintenance of outcrossing and explore other factors that may impede the spread of self-fertilization.

Session 1 MON GEN C 1

# Fitness consequences of parasite-mediated selection on sexual reproduction in a natural population (51671)

**Amanda Gibson**, Lynda Delph, Curt Lively.

*Indiana University.*

Sex is costly relative to asexual reproduction, yet it is widespread in nature. What force prevents sex from being out-competed? The Red Queen Hypothesis argues that coevolving parasites select for sex in hosts. Our study tests if parasites are a sufficient force to maintain sex in nature. Sexual lineages of a freshwater snail persist in competition with asexual forms, and a castrating trematode parasite has been indirectly linked to this persistence. We combine field sampling with experimental mesocosms to test if parasite selection alone can confer a fitness advantage to sexual individuals in competition with asexual clones. The Red Queen predicts that the fitness of sexuals relative to clones will be periodically higher in the presence vs. absence of parasites. At present, we find that sexuals are more parasitized than are clones, and that parasites lower the relative fitness of sexuals. Accordingly, long-term field data suggest that the frequency of sexual individuals is declining in the natural population. With multi-year sampling, we further test the Red Queen's prediction that the direction of parasite selection will shift to favor sex as clones increase in frequency. Our work provides a much-needed direct test of the Red Queen in a natural system.

Session 1 MON GEN C 1

# Brachionus calyciflorus evolves higher levels of sex with more loci under selection. (51689)

**Pepijn Luijckx**, Eddie Ho, Madjid Gasim, Connor Yanchus, Suyang Chen, Yuna Kim, Aneil Agrawal.

*University of Toronto.*
The widespread occurrence of sexual reproduction, despite its well-known costs, has been a long standing problem in evolutionary biology. Although there are numerous theories for why sex is the most common mode of reproduction, critically few assumptions and predictions of these theories have been tested. Using experimental evolution with the facultative sexual rotifer Brachionus calyciflorus we tested whether higher levels of sex evolve when more loci are under selection as predicted by Hill-Robertson interference, a popular theory for the maintenance of sex. The number of loci under selection were manipulated by adapting B. calyciflorus to either one, two or three abiotic stressors in a full factorial design (i.e. each multi stressor was composed of different combinations of the single stressors). Results from two independent evolution experiments (over one million animals scored) confirmed the hypothesis. B. calyciflorus produced more sexual eggs when adapting to more complex environments. Furthermore, common garden experiments confirmed that this change was genetic and as we standardize population size these changes where unlikely due to differences in genetic drift. These findings can explain why sex is the dominant mode of reproduction as natural populations may experience a multitude of selection pressures at any one time.

# How important are sex-linkage and non-additive genetic variation in the variance structure of sexually dimorphic traits? (52037)

**Daphne Fairbairn.**

*University of California, Riverside.*

Selection favoring different trait values in males and females is expected to favor the evolution of both sex-specific patterns of gene expression and sex-linkage. Although genomic and transcriptomic studies suggest that both mechanisms are important, quantitative genetic analyses often fail to find disproportionate effects of sex-linkage for sexually dimorphic traits. Non-additive interactions are also likely to be important for genes involved in sexual dimorphism, but the effects of these on genetic variances have been difficult to estimate independently of sex linkage. This presentation summarizes the results of a breeding experiment designed to estimate additive and non-additive, sex-linked and autosomal variances for 16 morphological traits in an insect with XX/XO sex determination, the water strider, Aquarius remigis. The traits range from sex-limited to sexually monomorphic and a subset is subject to strong sexual selection in males. The results reveal major differences in genetic architecture between sexes, often with disproportionate contributions of sex-linked genes and large non-additive effects. As predicted, sex-linkage is associated with lower between-sex genetic correlations. The relationships between genetic architecture, sexual dimorphism and the pattern of selection are broadly consistent with predictions from evolutionary theory, but several anomalies suggest avenues for future research.

# X-linkage of sex-specific genetic variance revealed using G-matrix analyses and a novel laboratory technique (51959)
**Robert Griffin**, Holger Schielzeth, Urban Friberg.

*Uppsala University; Bielefeld University; Linköping University.*

Intralocus sexual conflict can constrain the evolution of sex-specific phenotypic optima via correlated responses to selection. Genetic variance-covariance matrices, G-matrices, can be applied to data to estimate the variance within traits, and covariance between multiple traits, environments, and sexes. Several methods can then be used to describe and compare the characteristics and geometry of G-matrices and component sub-matrices. We use partial-hemiclones, a novel laboratory method using Drosophila melanogaster, which allows us to powerfully estimate X-chromosome and autosomal contributions to genetic (co)variance. Two G-matrices were constructed, for the X-chromosome and autosomes separately, containing (co)variance estimates for 3 traits (including longevity) in both sexes. Differences between these G-matrices are tested using multiple analytical methods, including the multivariate breeder's equation. Principally these are used to test for differences in the B-submatrix, which shows the intersexual genetic covariance, between the two types of partial-hemiclone lines. We show that more intersexual genetic covariance is found in the autosomes, suggesting that the X-chromosomes represent a hotspot for sex-specific genetic variance. Major sex chromosomes could therefore play a significant role in the resolution of intralocus sexual conflict.

# The geography of sex-specific selection, local adaptation, and sexual dimorphism (51691)

**Tim Connallon**

*Monash University.*

Local adaptation and sexual dimorphism follow parallel conceptual threads. Each represents an iconic evolutionary scenario of intra-specific adaptive differentiation in the face of gene flow, and each is associated with a set of influential theoretical predictions within its respective evolutionary context. Here, I merge theories of local adaptation in space, and sex-specific adaptation over time, and show that their confluence yields several unique predictions about the roles of context-specific selection, migration, and genetic correlations, in adaptive diversification. I specifically revisit two influential predictions from classical studies of clinal adaptation and sexual dimorphism: (1) that local adaptation should decrease towards species range margins; and (2) that opposing directional selection between the sexes (sexual antagonism) should accompany the evolution of sexual dimorphism. I show that both predictions often break down under clinically varying selection. The geography of local adaptation can be sexual dimorphic, with locations of relatively high and low local adaptation differing extensively between the sexes. Moreover, the intensity and duration of sexual antagonism is highly variable across the species range. Subpopulations near the range center are hotspots for sexual antagonism. Peripheral subpopulations exhibit a stronger alignment of directional selection within each sex.
# TRANSCRIPTOME-WIDE EFFECTS OF MALE SEXUAL SELECTION ON THE FATE OF NEW MUTATIONS (52609)

**Julie M. Collet**, Mark W. Blows, Katrina McGuigan.

*University of Queensland; University of Queensland; University of Queensland.*

Traits that determine male mating success are predicted to have widespread effects on sex-specific genetic variation as a consequence of the pleiotropic allelic effects of sexual and non-sexual traits. We manipulated the opportunity for sexual selection on males during 27 generations of mutation accumulation in inbred lines of Drosophila serrata. To complement previous analyses of the effects of male sexual selection on male and female phenotypes, we used a microarray platform to investigate the effect of sexual selection on the expression of 2689 genes. Over all genes, mutational variance in gene expression increased by an average 42%, in sexually selected lines, compared to lines that did not evolve under sexual selection. However, there was no significant effect of sexual selection on average gene expression. Our results provide clear evidence that sex-specific selection on males can generate widespread effects across the genome. An increase in mutational variance without a corresponding change in mean is consistent with divergence generated by widespread pleiotropic associations with traits affecting male mating success. Furthermore, a Gene Ontology term enrichment analysis comparing treatments will enable the identification of the functions targeted by male sexual selection.

# Red males revealed: a cytochrome P450 gene cluster controls production of derived red ketocarotenoids in the zebra finch bill (52724)

**Nick Mundy**, Jessica Stapley, Clair Bennison, Terry Burke, Tim Birkhead, Staffan Andersson, Jon Slate.

*Department of Zoology, University of Cambridge; Department of Animal and Plant Sciences, University of Sheffield; Department of Zoology, University of Gothenburg.*

Red coloration is commonly involved in sexual, social or interspecific colour signalling. Highly chromatic ("bright") red integument (skin, scales, feathers) in birds is typically caused by ketocarotenoids, such as canthaxanthin, which are metabolically derived from dietary yellow carotenoid precursors. However, this key molecular mechanism underlying sexual dichromatism in birds has remained obscure. Here we investigate the pigmentary, genetic and gene expression basis of the yellowbeak mutation in the zebra finch, an autosomal recessive mutation. Wildtype ketocarotenoids are absent in the beak and tarsus of yellowbeak birds. Using a candidate gene approach in a low resolution QTL analysis we identified a haplotype in the CYP2J2 cluster on chromosome 8 that is perfectly associated with the yellowbeak phenotype. The yellowbeak haplotype has a whole gene deletion of the second locus (CYP2J2B) in the cluster. CYP2J2B is specifically expressed in ketocarotenoid-coloured beak and legs of wildtype zebrafinches but not in liver. Our results suggest that CYP2J2B is
essential for the sexually selected red beak of the zebra finch, that it likely encodes a
functional C4 ketolase enzyme, and that the conversion is primarily peripheral in this species,
i.e. in the ketocarotenoid-pigmented tissues.

# Identifying the causes of natural selection: What have we learned from 25 years of experiments? (53330)

**Christina Caruso.**

*Department of Integrative Biology, University of Guelph.*

Phenotypic selection varies in space and time. To understand why there is variation in selection, we need to identify which environmental factors cause traits and fitness to covary. One way to identify these factors was described by Wade and Kalisz (1990): experimentally manipulate the environment and measure selection within each treatment group. If the manipulated environmental factor causes traits and fitness to covary, then selection will differ between treatment groups. Although this experimental approach to identifying the causes of selection was described 25 years ago, the results of these experiments have yet to be reviewed.

I will review what 25 years of ecological experiments have, and have not, taught us about the causes of natural selection. First, I will use a case study of selection on floral traits of the wildflower Lobelia siphilitica to illustrate how experimental manipulations can be used to test longstanding assumptions about the causes of selection. Second, I will use a meta-analysis of selection estimates from experimental studies published over the last 25 years to test two hypotheses about the relative importance of different causes of selection. I will conclude by describing priorities for the next 25 years of experimental studies of the causes of selection.

# The fluctuation of selection and its evolutionary consequences in an alpine rodent population. (51725)

**Timothée Bonnet, Erik Postma.**

*Institute of Evolutionary Biology and Environmental Studies.*

Temporal variation in the strength and direction of directional selection has important implications for the maintenance of genetic variation and for the prediction of evolutionary change in wild populations. However, empirical estimations of the fluctuation of selection, together with the genetic response, are still scarce and hampered by confounding sampling variance.

Using the long-term monitoring of a wild snow vole (Chionomys nivalis) population, we quantify the temporal fluctuation of the selection acting on morphological traits, while
accounting for sampling variance. Climatic factors appear as a possible driver of change in the strength and direction of selection. Moreover, contrasting patterns of fluctuation among viability, fertility, and total selection highlight the importance of considering all fitness components. We then relate the fluctuation of selection to year-by-year genetic changes, using both a candidate gene approach and multivariate quantitative genetic models. This provides a direct test of whether fluctuation can explain evolutionary stasis in this population, and illustrate that the selection patterns observed at the phenotypic level do not necessarily translate into parallel genetic changes.

# Measuring fluctuating phenotypic selection (53320)

**Luis-Miguel Chevin**, Marcel Visser, Jarle Tufto.

CNRS.

Fluctuating selection caused by randomly changing environments is a ubiquitous feature of natural systems. The magnitude and predictability of these fluctuations are expected to strongly impact the evolution and demography of populations, but few attempts have been made to quantify these parameters and relate them to relevant environmental variables, in a way that connects to theoretical predictions. In this talk, I will first briefly review theoretical results for evolutionary demography in a randomly changing environment affecting the optimum phenotype for a quantitative trait. I will then discuss some of the challenges with measuring fluctuating selection using classical methods such as selection gradients. Finally, I will introduce an approach for estimating patterns of changes in an optimum phenotype, which allows inferring parameters that directly appear in theoretical predictions. This will be illustrated by an application to the breeding time of a population of great tits in the Netherlands, a classic example of evolution in response to climate change.

# The Spatial Scale of Local Adaptation (51756)

**Jarrod Hadfield**, Albert Phillimore.

University Of Edinburgh; University Of Edinburgh.

The distribution of phenotypes in space will be a compromise between local adaptation increasing the fit of phenotypes to local conditions and gene-flow reducing that fit. Few theoretical models have considered the evolution of quantitative characters on spatially explicit landscapes, and those that have, only consider scenarios where optimum trait values change as a deterministic function of space, such as clines. Here we extend these models to include a stochastic spatially autocorrelated aspect to the environment, and as a consequence the optimal phenotype. We show that under these conditions the regression of phenotype on the environmental variable becomes steeper as the spatial scale on which individuals, or
populations, are sampled becomes larger. Under certain deterministic models - such as
smooth clines - the regression is constant. The way in which the regression changes with
spatial scale is informative about the degree of phenotypic plasticity, the relative scales of
effective gene flow and environmental autocorrelation, and the environmental dependency of
selection. Methods to estimate these parameters from spatially replicated data are discussed,
and the theory suggests a common scale on which temporal and spatial fluctuations in
selection can be compared.

DETECTING CHANGING SELECTION INTENSITIES FROM TIME-SAMPLED DATA (51758)

Hyunjin Shim, Stefan Laurent, Matthieu Foll, Jeffrey D. Jensen.

*Ecole Polytechnique Fédérale de Lausanne (EPFL); Swiss Institute of Bioinformatics (SIB);*
*International Agency for Research on Cancer.*

The possibility of fluctuating selection in natural populations was suggested by Wright (1948) during his famous controversy with Fisher regarding the phenotypic dataset of Panaxia dominula, and the subject has since been considered in various analyses - ranging from Kimura (1954) to Cain et al. (1990). Until now, the focus of discussion mainly centered on the random fluctuation of selection intensities. Here, we present a novel method to consider nonrandom fluctuation of selection intensities using ABC-based approaches, in order to detect and evaluate the change in selection strength in time-sampled data. The novel method estimates jointly the position of a change point and the strength of both corresponding selection coefficients (as well as dominance for diploid cases) from the allele trajectory. Furthermore, the method is applied on the historical dataset of Panaxia dominula to test for a change in selection intensity, as well as on a whole-genome time-serial study of influenza virus in order to identify mutations with changing selection intensities in response to drug treatment.

The gibbon genome: swinging between evolution, speciation and disease
(53396)

Lucia Carbone.

Oregon Health & Science University.

Gibbons are small Asian apes heavily threatened by extinction. They carry many distinctive
traits that set them apart from their close relatives, human and the great apes, including
brachiation (i.e. locomotion mainly using their upper limbs), pair bonding, and duet singing to
advertise their territory. Their most striking trait, however, is the unusually high number of
chromosomal rearrangements. There are four gibbon genera (Nomascus, Hoolock, Hylobates,
and Symphalangus) that split from each other only 5 million years ago and each of them
carries a distinct karyotype with chromosome numbers ranging from 38 to 52. This
exceptional accelerated karyotype evolution makes gibbons an ideal model to study
chromosome evolution and mechanism of genome instability. Together with geographical
changes occurring in their territory, the abundance of chromosomal rearrangements was
responsible for an “instantaneous” radiation of the gibbon genera and the higher number of
species (n=19) found in the gibbon family. We discovered that a gibbon specific
retrotransposon, the LAVA element, inserted in genes involved in chromosome segregation,
suggesting that in these species chromosome fragility might have been triggered by mis-
segregation during meiosis. This phenomenon has recently been characterized in cancer
genomes and embryo development, highlighting an analogy between mechanisms underlying
genome instability during species evolution and disease.

Fitness consequences of inversion polymorphisms in the zebra finch (51889)

Wolfgang Forstmeier, Ulrich Knief, Georg Hemmrich-Stanisak, Michael Wittig, Andre Franke, Simon Griffith, Bart Kempenaers.

Max Planck Institute for Ornithology; Institute of Clinical Molecular Biology; Macquarie University.

Genome-wide scans for signatures of past selection can help identify loci with strong effects on fitness. In the present study, we searched for patterns in the allele frequency spectrum across genomic regions among 23,000,000 SNPs identified from pool-seq data of genomic DNA from 100 wild-caught zebra finches. Using sliding windows of a measure of pooled heterozygosity, we found several genomic regions where the great majority of SNPs showed a minor allele frequency close to 50%. Subsequent genotyping of 3,804 SNPs spread across these regions and the entire genome in 948 wild zebra finches identified these regions as break points of inversion polymorphisms. Altogether, we found that 4 out of 31 covered chromosomes harbored inversion polymorphisms that span between 13 and 60 megabases and cover large proportions of the affected chromosomes with inversion frequencies close to 50%, which is suggestive of balancing selection resulting from heterozygote advantage. Hence, we studied phenotypic effects of these inversions on morphology, relative fitness and embryo mortality in up to 6,000 mostly captive zebra finches to gain an understanding of the selective forces that lead to the maintenance of these remarkable polymorphisms.

Human Evolution by Segmental Duplication (53374)

Evan Eichler.

University of Washington & HHMI.
Human duplicated sequences show extraordinary sequence complexity and are important
sources for gene innovation and rearrangement associated with neurocognitive diseases such
as autism and intellectual disability. Evolutionary genomic reconstructions point to a burst of
segmental duplications in the common ancestor of human and the apes in contrast to other
mutational processes that have slowed at this point in time. I will show that much of the
interspersed human duplication architecture is focused around core duplicons corresponding
to the expansion of gene families, which show strong signatures of positive selection and
which lack orthologs in other mammalian species. I will present an overview of the evolution
of human-specific segmental duplications, their copy number variation in diverse human
populations and their potential to form neofunctional gene fusions. I will highlight novel
genes that have evolved within the human lineage and appear to have contributed to adaptive
aspects of human brain function as well as examples where this evolutionary plasticity has
been positively selected. Using single-molecule real-time (SMRT) sequencing technology, I
will show how such complex regions can be resolved and show how radically these regions of
our genome have changed and differ among human populations. Paradoxically, the
duplication architecture complexity has led to a high background rate of copy number
variation mutations associated with neuropsychiatric and neurodevelopmental disease in the
human species suggesting that novel adaptations and increased disease burden are linked.

Parental investment predicts genetic diversity of animal species (52005)

Jonathan Romiguier, Nicolas Galtier.

University of Lausanne; CNRS.

Genetic diversity is the amount of variation observed between DNA sequences from distinct
individuals of a given species. This pivotal concept of population genetics has implications
for species health, domestication, management and conservation. Levels of genetic diversity
seem to vary greatly in natural populations and species, but the determinants of this variation,
and particularly the relative influences of species biology and ecology versus population
history, are still largely mysterious. Here we show that the diversity of a species is
predictable, and is determined in the first place by its ecological strategy. We investigated the
genome-wide diversity of 76 non-model animal species by sequencing the transcriptome of
two to ten individuals in each species. The distribution of genetic diversity between species
revealed no detectable influence of geographic range or invasive status but was accurately
predicted by key species traits related to parental investment: long-lived or low-fecundity
species with brooding ability were genetically less diverse than short-lived or highly fecund
ones.

A genomic study of the contribution of DNA methylation to regulatory evolution in primates (52018)
**Julien Roux**, Irene Hernando-Herraez, Nicholas Banovich, Raquel Garcia-Perez, Jonathan Pritchard, Tomas Marques-Bonet, Yoav Gilad.

*University of Lausanne; University of Chicago; Institute of Evolutionary Biology (UPF-CSIC), PRBB, Barcelona; Howard Hughes Medical Institute, Stanford University; Departments of Biology and Genetics, Stanford University.*

A long-standing hypothesis is that changes in gene regulation play an important role in adaptive evolution, notably in primates. Yet, in spite of the evidence accumulated in the past decade that regulatory changes contribute to species-specific adaptations, we still know little about the mechanisms of regulatory evolution. In this study we focused on DNA methylation, an epigenetic mechanism whose contribution to the evolution of gene expression remains unclear.

To interrogate the methylation status of the vast majority of cytosines in the genome, we performed whole-genome bisulfite conversion followed by high-throughput sequencing across 4 tissues (heart, kidney, liver and lung) in human, chimpanzee and macaque. In parallel, we collected gene expression profiles using RNA-seq from the same tissue samples, allowing us to perform a high resolution scan for genes and pathways whose regulation evolved under natural selection.

We integrated these datasets to characterize better the genome features whose methylation status leads to expression changes across tissues and species. We discovered that, in contrast to the well-known negative association between gene expression and methylation changes across tissues, the association between these two variables was greatly reduced across species. Our study questions the role of epigenetic modifications as a mechanism causing regulatory changes in primates.

# Recombination and GC-biased gene conversion shape genome evolution in the honeybee (Apis mellifera) (52102)

**Andreas Wallberg**, Sylvain Glémin, Matthew T Webster.

*Department of Medical Biochemistry and Microbiology, Science for Life Laboratory, Uppsala University; UMR 5554, Institute of Evolutionary Sciences, University of Montpellier.*

Recombination is crucial for sexual reproduction and has pervasive effects on genetic diversity. The eusocial honeybee Apis mellifera has among the highest recombination rates observed in any eukaryote (~22 cM/Mb). The reasons for these high rates and their effects on genome evolution are unknown. We have used whole-genome resequencing data from 30 honeybees to build a fine-scale map of recombination from patterns of linkage disequilibrium. We have studied the associations between recombination, DNA methylation, gene expression and the site frequency spectrum to assess how recombination shapes the honeybee genome.

We find that recombination frequencies are not highly variable nor restricted to hotspots, in contrast to many sexual plants, fungi and vertebrates. They are greatly influenced by germline
CpG-methylation, which suppresses recombination. The site frequency spectrum is highly skewed towards the fixation of GC alleles, indicative of a major impact of GC-biased gene conversion (gBGC), which we estimate as 5-50x higher than in humans. The fixation bias specifically favours mutations that generate CpG sites, which occur in excess in honeybees.

Recombination determines levels of genetic variation in honeybees. At such high rates, gBGC strongly interferes with selection, resulting in rapid fixation of deleterious alleles and altered nucleotide composition across the genome.

# Stalking the elusive generalist: Understanding the relationship between the fundamental and realized niches of Pseudomonas in the home (53353)

Susanna Remold.

*University of Louisville.*

Many species of Pseudomonas have the ability to use a variety of resources and have been isolated from diverse environments, and as a result, Pseudomonas are often characterized as having broad fundamental niches. In culture-based and culture-independent surveys of a broad range of environments found in and around the human home, we assessed the degree to which Pseudomonas' realized niches, where they are actually found in nature, are equally broad. We found temporal and spatial variability in recovery of the three species groups of Pseudomonas most commonly found in homes: the P. aeruginosa, P. fluorescens and P. putida species groups. In addition, we found that these Pseudomonas species groups' distributions also differ from each other. In a series of studies characterizing strains collected in these surveys and individually and in pairwise interactions, we explored biotic and abiotic factors that may cause Pseudomonas' realized niches to differ from each other, and to be smaller than their fundamental niches. In my talk I will describe some of these studies and discuss applications of studies linking fundamental to realized niches.

# Sub-inhibitory antibiotic concentrations can radically alter the eco-evolutionary consumer-resource dynamics in microbial communities (51684)

Teppo Hiltunen, Lutz Becks, Matti Jalasvuori, Ville Ojala, Jouni Laakso.

*University of Helsinki; Max Planck Institute for Evolutionary Biology; University of Jyväskylä.*

Modern medicine relies heavily on the effective use of antibiotics. However, antibiotic resistant pathogens are on the rise. This problem has been often studied in simplified single species setting, but in natural environments bacteria reside in multispecies communities where they interact with other microbes. Yet, virtually nothing is known about community aspects,
such as how predation affects the emergence and spread of antibiotic resistance. Furthermore, recent evidence highlights the importance of sub-inhibitory concentrations of antibiotics on bacteria. In addition to the fact that these low concentrations can alter the bacterial gene expression, communication, and select for antibiotic resistant genotypes, an important question is whether this modifies the community level dynamics. By using experimental evolution methods with a microbial model system consisting of bacterial prey, Pseudomonas fluorescens SBW25, parasitic phages and protozoan predators, we found that subinhibitory concentrations of antibiotic streptomycin can radically alter the eco-evolutionary community dynamics. Moreover, the community structure determined the emergence of antibiotic resistant genotypes in the bacterial population. In addition to the phenotypic data, also a massive re-sequencing of the experimental Pseudomonas populations is underway. Our results highlight the importance of understanding the eco-evolutionary community aspects when fighting the antibiotic resistance problem.

# Experimental evolution of bacteria in the laboratory and in the wild (53482)

**Tom Bell.**

*Imperial College London.*

Understanding how species adapt to novel environments is among the greatest challenges in evolutionary biology. However, experimental studies and theories have focused almost exclusively on simplified systems containing at most a few species. If species interactions in natural communities fundamentally alter evolutionary outcomes, then there is a need to study the adaptive process within the context of entire communities, and to understand the consequences of adaptation for community structure and functioning. I will discuss a series of experiments using bacterial microcosm communities of increasing complexity. When challenged with a novel environment, the evolutionary dynamics of mixtures of a few species differ substantially from those grown as single species, and species interactions evolve over time, resulting in a change in the functioning of the entire community. The outcome appears to depend critically on the diversity of the surrounding community, suggesting a complex interplay between ecological and evolutionary processes.

# Bacterial biodiversity: the role of spatial structure and competition within species (51688)

**Anne Leinweber, Rolf Kümmerli.**

*University of Zurich.*

Bacteria often live in multispecies communities, which is difficult to explain, because strongly competitive species should eventually displace weaker counterparts. Spatial structure
has been suggested to stabilize diversity by separating competitors from each other.
Alternatively, it has been proposed that strong competitors are more prone to within-species
competition, which can relax between-species competition.

To test these hypotheses, we use Pseudomonas aeruginosa (PA) and Burkholderia
cenocepacia (BC), two bacterial species naturally co-occurring in soil and human
opportunistic infections. However, under standard laboratory conditions PA eradicates BC.
We manipulated spatial structure by growing the bacteria in medium with varying viscosities.
To manipulate within-species competition, we introduced a PA cheating mutant strain to co-
cultures. Under the iron limited conditions of our experiments, this mutant is able to exploit
the iron scavenging siderophores secreted by the wildtype PA.

Using a mixture of competition assays and experimental evolution, we found that spatial
structure consistently inhibited species co-existence. Within-species competition, meanwhile,
promoted co-existence in unstructured habitats, because it allowed cheats to efficiently exploit
PA, which eased the competitive burden of PA on BC. Thus, we identified within-species
competition as an important driver of long-term species coexistence.

Experimental coevolution and the effects of parasite species co-infection on
parasite virulence and fitness (51718)

<u>Suzanne Ford</u>, Kayla King.

University of Oxford.

The simultaneous infection of a single host by multiple parasite strains and species, termed co-infection, is common in nature. Co-infecting parasites that share ecological niches within the host compete for space and resources in numerous ways. This competition is likely to impose selection on interacting parasites and as such could play a role in shaping host-parasite coevolutionary trajectories. Importantly, the degree to which co-infection affects the evolution of key parasite traits such as competitive ability and virulence is uncertain. In this project we experimentally coevolved two bacterial parasites, Enterococcus faecalis and Staphylococcus aureus, by serially co-infecting them within a non-evolving host organism, Caenorhabditis elegans. Firstly, we found that coevolved S aureus gained a significant competitive advantage under co-infection compared to singly evolved controls and became locally adapted in time to it's competitor, E faecalis. Secondly, we found that parasite species co-infection significantly altered the evolved level of intrinsic virulence of both species compared to singly evolved controls. Together, our results support the hypothesis that parasite species co-infection could be a selective factor in the evolution of key parasite traits. This further suggests that interspecific interactions between parasites could play a role in shaping coevolutionary interactions between parasites and their hosts.

Pathogen adaptation to individual and social host defences in ants (51808)
Miriam Stock, Anna V. Grasse, Sylvia Cremer.

IST Austria (Institute of Science and Technology Austria), Austria.

In co-evolving host-pathogen systems, both players undergo continuous adaptations. For social insect hosts, these include individual behavioural and immunological adaptations, and their collectively performed, social disease defences. We performed an evolution experiment testing for pathogen adaptation of an insect-pathogenic fungus to an ant host. A genetically diverse starting population of the pathogen – consisting of a mix of naturally co-occurring fungal strains isolated from the field – was let to adapt to the ants over 10 host passages under two different conditions: (1) a single host treatment, involving only the individual defences of the exposed ant, and (2) a social host treatment, in which the exposed ant was accompanied by nestmates, allowing for additional collective disease defences. Fungal diversity decreased drastically by competitive strain exclusion in both treatments, yet a greater variation remained among replicates in the social host treatment. Testing the evolved fungal lines from both treatments under both single and social rearing conditions revealed an effect of 'evolution history' on pathogen killing rate and transmission stage production, as well as on the induction of host sanitary behaviours. We conclude that the additional collective disease defences in insect societies add selection pressures on coevolving pathogens affecting their ability to adapt to the host at the group level.

Session 1 MON MAX 410 6

# The social side of sex: Male/female coevolution and social plasticity affect reproductive patterns (53319)

Suzanne Alonzo.

Department of Ecology and Evolutionary Biology, University of California Santa Cruz.

Extensive empirical and theoretical research has focused on understanding the diversity of reproductive patterns and behavioral interactions observed in nature. I have argued that considering both coevolutionary dynamics and social interactions can improve our ability to explain and predict this striking variation. In my talk, I will discuss why these dynamics are essential for understanding the evolution of male and female reproductive traits. I will first present the results of some general theory examining how social interactions affect evolutionary dynamics and discuss extensions of this theory to our understanding of specific reproductive behaviors. I will then present some data on how interactions between the sexes at mating and fertilization affect sexual selection, potentially driving the evolution of sperm allocation and paternal care in a Mediterranean fish (the ocellated wrasse, Symphodus ocellatus). Finally, I will discuss what these and other similar empirical patterns have to say about what theory and data are needed if we wish to improve our understanding of and capacity to predict the diversity of reproductive patterns observed in nature.
# Promiscuity modulates the male Bateman gradient in Drosophila melanogaster (51636)

**Juliano Morimoto**, Grant C. McDonald, Tommaso Pizzari, Stuart Wigby.

*University of Oxford.*

Sexual selection favours genes that increase success in intra-sexual competition. In a classic study, Angus Bateman measured the association between the number of mates and offspring production (the “Bateman gradient”) and found that the gradient was more positive for males than for females, which Bateman interpreted as evidence for stronger intra-sexual competition in males. Although Bateman’s study has had a strong influence on the field of sexual selection – and the Bateman gradient is widely used to measure the strength of sexual selection – Bateman’s principles only address competition for mates (pre-copulatory sexual selection), thus ignoring the effects of differential fertilisation success. Here, we genetically manipulated mating frequency in female D. melanogaster and found that in populations with significantly increased promiscuity (i.e. both females and males have more sexual partners), the male Bateman gradient is significantly reduced whereas female Bateman gradients are unaffected (i.e. non-significantly positive). Our study complement Bateman’s paradigm by providing direct empirical evidence of the effects of promiscuity on pre- vs post-copulatory sexual selection in males. In addition, our study corroborates a central expectation in sexual selection field, namely that the main driver of sexual selection in males switches from pre-copulatory to post- copulatory in high promiscuous populations.

Session 1 MON MAX 410 6

# Coalescence and genomics with linked selection in systems with bi- and uniparental reproduction: contrasting partial asexuality and selfing (53310)

**Aneil Agrawal.**

*University of Toronto.*

Much of evolutionary genomic inference relies on coalescence but most previous theory assumes full sex (or haploidy). We have been integrating partial asexuality in diploids into the coalescent framework to understand how low rates of sex affects coalescence, especially in the presence of background and balancing selection. Low rates of sex greatly enhance background selection, thereby reducing effective population size, via both a recombination effect and a segregation effect. Total background selection tends to be stronger with partial asexuality than with selfing, but linked and unlinked loci contribute differently under these alternative reproductive systems. In contrast to background selection, balancing selection increases the coalescent time for a linked neutral site. With partial asexuality, the effects of balancing selection are increased via a recombination effect but reduced through a segregation effect. In contrast, with selfing, both recombination and segregation effects enhance the consequences of balancing selection. Finally, I will discuss these theoretical results with respect to the (preliminary) interpretation of our new population genomic data from a facultatively sexual plant, the duckweed Spirodela polyrhiza.
# Genetics of attractiveness and mate choice in Drosophila melanogaster (51690)

Devin Arbuthnott, Daniel Promislow.

*University of Washington.*

The genetic and physiological control of mate choice and mate competition has broad implications for the evolution of sexually selected traits and mating systems. While particular mutations and manipulations of specific metabolic pathways have illustrated important regions of control for attractiveness and mate choice, little is known about the extent and nature of genetic variation for these traits in natural populations. We measured attractiveness and mate choice traits among the Drosophila Genetic Reference Panel to quantify variance and genetically map these traits. There was significant and substantial genetic variation in female attractiveness and male choosiness among these inbred lines of Drosophila melanogaster. Furthermore, we identified several significant genetic regions explaining this variance, including genes influencing growth and energy metabolism. However, there was no overlap in the regions influencing female attractiveness and male choosiness, nor was there any phenotypic correlation between these traits. Our work sheds light on the genetic control of sexually selected traits, which broadens our understanding of the evolution of sexual traits and its interaction with developmental pathways.

# Does sexual selection augment or oppose natural selection? (51715)

Luke Holman.

*Australian National University.*

Sexual selection has been portrayed as both a friend and a foe of natural selection. The degree of alignment between natural and sexual selection is difficult to measure fully, yet has ramifications for diverse topics including conservation biology, the evolution of sex, and the speed of adaptation. Here, I discuss experiments measuring the effects of sexual selection on adaptation and naturally-selected fitness components in beetles. I first ask whether sexual selection helps to clear radiation-induced mutations that harm survival and fecundity. Next, I use experimental evolution to show that populations founded by polyandrous females are substantially fitter than those founded by singly mated females. Thirdly, I test whether sexual selection impedes or enhances the speed of adaptation to pesticide using experimental evolution. The experiments reaffirm that sexual selection can both help and harm targets of natural selection such as fecundity and survival, and highlight that sexual selection has a role to play in dispersal ecology and the evolution of resistance.
# Sexually transmitted infection and the evolution of serial monogamy (51732)

**David McLeod**, Troy Day.

*Queens University.*

The selective forces shaping mating systems have long been of interest to biologists. One particular selective pressure that has received comparatively little attention is sexually transmitted infections (STIs). While it has been hypothesized that STIs could drive the evolutionary emergence of monogamy, there is little theoretical support. Here we use an evolutionary invasion analysis to determine what aspects of pathogen virulence and transmission are necessary for serial monogamy to evolve in a promiscuous population. We derive a biologically intuitive invasion condition in terms of population-specific quantities. From this condition, we obtain two main results. First, when pathogen virulence causes mortality rather than sterility, monogamy is more likely to evolve. Second, we find that at intermediate pathogen transmission rates, monogamy is the most selectively advantageous, whereas at high- and low-transmission rates, monogamy is generally selected against. As a result, it is possible for a pathogen to be highly virulent, yet for promiscuity to persist.

Session 1 MON POL D 34

# Inversions as barriers to recombination and facilitators of speciation: Studies in Drosophila pseudoobscura/ D. persimilis (51934)

**Mohamed Noor**, Katharine Korunes.

*Duke University.*

Many studies suggest that limiting recombination in species hybrids may facilitate the persistence of the hybridizing species. Chromosomal inversions, thought to have limited recombination/ gene flux in hybrids, exhibit greater nucleotide differentiation between species than uninverted regions, and inversions preferentially harbor factors associated with speciation-related traits. However, the effectiveness of inversions as barriers to gene flux has been inferred primarily from patterns in natural populations. This talk presents results obtained thus far attempting to measure reductions in gene flux associated with inversion heterozygosity directly in laboratory populations, and relates these findings to existing theoretical models on the role of inversions in speciation.

Session 1 MON POL D 34

# Genome divergence during early stage speciation with gene flow (51640)

**David A. Marques**, Laurent Excoffier, Ole Seehausen.
The number of speciation studies using population genomics approaches has increased quickly, yet few have compared replicate events of the same process with variation in geographical opportunity for gene flow between incipient species. We studied genome-wide differentiation among threespine stickleback (Gasterosteus aculeatus) lake and stream ecotypes that evolved in the last 150 years within the Lake Constance drainage system. We tested predictions of speciation with gene flow theory by comparing genomic differentiation between lake and stream ecotypes breeding in sympatry versus in parapatry. Consistent higher gene flow, we found fewer genomic islands of differentiation and lower genome-wide levels and heterogeneity of differentiation in the sympatric case. However, 15 genomic islands of differentiation resisting gene flow in sympatry showed parallel divergence and are thus candidate regions for adaptive divergence among lake and stream ecotypes. Interestingly, 12 of these islands cluster in a low-recombination region on chromosome VII. Furthermore, islands showed non-random overlap with many known quantitative trait loci, most of them controlling phenotypic traits divergent between Lake Constance ecotypes. The genomic co-localization of parallel differentiation, trait architecture and recombination landscape suggests that both divergent natural selection and the genomic arrangement of heritable traits are important in adaptation and early stage ecological speciation with ongoing gene flow.

The multifarious histories charting the multifaceted landscapes of genomic
differentiation (53342)

Nicolas Bierne.

University of Montpellier.

One of the most striking and consistent results of genome-wide surveys of differentiation is the heterogeneity of differentiation across the genome, including highly differentiated regions, sometimes called “genomic islands of differentiation”. Several theories have been proposed to explain this pattern: (i) speciation with gene flow driven by local adaptation, (ii) background selection and hitchhiking in low recombining regions and (iii) variable persistence after secondary contact of differences accumulated in allopatry. I will first recall that the contrasted spatial structures between island and non-island genomic regions or the argument that adaptation to a new environment is recent, by no way can provide evidence for one or the other hypothesis. The history needs to be reconstructed from gene genealogies, and methods do not cease improving. It has recently become possible to account for genome-wide heterogeneity (GWH) in introgression rates or in effective population size. This has proven to have profound impacts on the biological conclusions drawn from the inference. We have applied these methods to a large RNAseq dataset of 70 pairs of taxa of animals that were not initially chosen to champion one or another model of speciation. We show that the existence of ongoing gene flow is robustly detected but the timing of gene-flow during divergence is difficult to infer, that GWH is widespread and needs to be accounted for, and initiate a
description of the relationship between divergence and genome porosity from this kind of
analysis.

Evolution of genome differentiation across the speciation continuum: From
patterns to mechanisms to regions related to species-specific evolution (51805)

**Reto Burri**, Alexander Nater, Takeshi Kawakami, Carina F. Mugal, Pall I. Olason, Linnea Smeds, Alexander Suh, Dutoit Ludovic, Hans Ellegren.

*Uppsala University.*

Recent studies have documented distinct and widespread regions of elevated differentiation ('differentiation islands') across genomes, but it remains unclear how the differentiation landscape evolves as speciation advances, which processes drive the evolution of differentiation islands, and ultimately how differentiation islands are related to speciation. Based on 200 re-sequenced genomes from 10 populations of four Ficedula flycatcher sister species, we show that differentiation islands evolve in structured populations as the result of background selection and divergent selection in genomic regions of low recombination. The heterogeneous differentiation landscape starts emerging among populations within species, and evolves recurrently among independent lineages. Together with the absence of pervasive gene flow in this model system, this demonstrates that a heterogeneous landscape of differentiation is not a consequence of speciation. We show how accounting for the mechanisms underlying the heterogeneous differentiation landscape using phylogenetic controls enables the identification of genome regions related to species-specific evolution.

Genome-wide tests for introgression between cactophilic Drosophila implicate
a role of inversions during speciation (51823)

Konrad Lohse, Magnus Clarke, Michael G. Ritchie, William J. Etges.

University of Edinburgh; University of Sheffield; University of St. Andrews; University of Arkansas.

Models of speciation-with-gene-flow have shown that the reduction in recombination between alternative chromosome arrangements can facilitate the fixation of locally adaptive genes in the face of gene flow and contribute to speciation. However, it has proven frustratingly difficult to show empirically that inversions have reduced gene flow and arose during or shortly after the onset of species divergence. We present an analysis of whole genome data from a pair of cactophilic fruit flies, Drosophila mojavensis and D. arizonae, which are reproductively isolated in the wild and differ by several large inversions on three chromosomes. We found an increase in divergence at rearranged compared to colinear chromosomes. Using the density of divergent sites in short sequence blocks we fit a series of
explicit models of species divergence in which gene flow is restricted to an initial period after
divergence and may differ between colinear and rearranged parts of the genome. These
analyses show that D. mojavensis and D. arizonae have experienced post- divergence gene
flow which ceased around 270 KY ago and was significantly reduced in chromosomes with
fixed inversions. Moreover, we show that these inversions most likely originated during or
after the onset of species divergence as predicted by theoretical models of speciation with
gene flow.

Traversing the micro-evolution to macro-evolution boundary in
Caenorhabditis nematodes with full-genome population genomics, crosses, and
hybrid phenotypes (52010)

<u>Asher Cutter.</u>

*University of Toronto.*

How do population processes translate into evolutionary divergence in genomes and
development between species? We are applying full-genome sequencing of Caenorhabditis
nematode individuals to characterize the influence of recombination, selection, and selfing vs.
outbreeding life history on patterns of population variation and divergence between sister
species. In the highly selfing C. briggsae, we find that long stretches of genetic linkage
interact with selection to severely reduce genetic variation across much of the genome. This
selection at linked sites also exerts its influence on genomic patterns of differentiation
between divergent populations. Analysis is ongoing for the outbreeding, partially
reproductively-isolated sister species C. remanei and C. latens, which are known to have
enormous effective population sizes and extremely high densities of polymorphisms and so
may permit exceptionally fine-scale resolution of selection in their genomes. Coupled with
classic genetic crosses and recombinant strain libraries within and between species, we have
mapped aspects phenotypic divergence and reproductive incompatibility with the goal of
integrating this with inferences about contemporary selection pressure and functional
mechanism.

Linking patterns and processes across scales: a case study with Neotropical
hummingbirds (53334)

<u>Catherine Graham.</u>

A fundamental challenge for ecology and evolution is connecting broad scale biogeographical
and macro-evolutionary mechanisms with local scale patterns of diversity. Community
phylogenetics attempts to create this link by evaluating patterns of relatedness, and often trait
similarity, among co-occurring species at multiple sites to generate hypotheses about the role
of different mechanisms governing community assembly. In Neotropical hummingbirds,
biogeographic studies show that closely related species co-occur less frequently than expected when compared to a species pool that considers environmental filtering or predicted species range overlaps. This pattern may result from limiting similarity and competitive exclusion of closely related species. However, traits that should influence these mechanisms are not highly conserved and community level analyses of phylogenetic and trait spacing does not always correspond. As a result, the precise role of limiting similarity and niche conservatism in influencing local assemblages is difficult to infer from biogeographic patterns alone. This is perhaps because competition occurs among individuals in local assemblages and cannot be deduced from broad-scale studies. In contrast, local scale studies often use manipulative experiments to evaluate how competition affects specific ecological processes. However, generalization of local scale studies across different assemblages or to broader geographic extents remains elusive. To address this scale mismatch we present an experiment which evaluates if hypotheses developed at biogeographic scales are consistent with local scale observations of competition in Neotropical hummingbirds. This study provides an initial link between patterns established by broad scale biogeography and mechanisms learned from local scale community ecology.

# Using low coverage multispecies genomic data to reconstruct the assembly of a widespread insect community (51821)

**Lynsey Bunnefeld**, Jack Hearn, Konrad Lohse, Graham N. Stone.

*University of Edinburgh.*

Whether biologically widespread communities assemble through codispersal of associated lineages (host tracking) or local recruitment (ecological sorting) remains an open question. The answer is central to our understanding of the temporal and spatial scales of multispecies interactions such as coevolution. Sequence data has been used to understand the relationships of populations within species, but inference has usually been limited by the small numbers of loci analysed. While short read sequencing allows generation of data for very large numbers of loci, model-based inference has been limited by a lack of methods suitable for data processing and analysis beyond a handful of model organisms. We have developed an efficient maximum likelihood method that can use de novo low-coverage genome assemblies to fit explicit models of community history. We use our method to assess the evidence for host tracking and ecological sorting models during the assembly of a community of herbivorous gallwasps and parasitoid wasp natural enemies, each sampled from a longitudinal series of Pleistocene glacial refugia spanning the Western Palearctic. Our inference framework is extremely flexible, requires no prior genetic resources and can be extended to assess support for a wide range of demographic histories.

# Comparative population genomics for community-scale demographic inferences (53313)
**Mike Hickerson.**

*City University of New York.*

The historical dynamics and evolution of natural biological communities is critical for understanding how communities respond to invasions, extinctions and can shift with adaptive evolution associated with ongoing climate change. One approach to understanding how whole communities respond to changes in climate and landscape is to use data and methods from the dynamic and exploding field of population genomics. Inferences from population genomics can make detailed inference about the demographic and evolutionary history of a species and by making community-level inference using aggregated data across taxa, researchers can better understand how changes in climate and landscape can drive or destroy regional patterns of biodiversity as well as ask whether groups of presently co-occurring species tracked each other in space and time through cycles of global climate shifts. To illustrate an application of this approach, I present an inferential hierarchical model of multi-species demographic history that makes use of high density SNP data sampled from co-distributed species. As genomic data becomes routinely collected from non-model taxa, researchers will be able to better test hypotheses about the varied and/or parallel responses to climate and landscape changes that affected whole communities.

**Ecological correlation reinforcement facilitates collective community behaviours without group selection (51958)**

**Daniel A. Power, Richard A. Watson, Eörs Száthmary.**

*University of Southampton, Electronics & Computer Science; University of Southampton, Institute for Life Sciences/Electronics & Computer Science; The Parmenides Foundation, Center for the Conceptual Foundations of Science.*

Ecosystem population dynamics are shaped by evolution and coevolution amongst their component species. Adaptations to biotic and abiotic environments modify interactions between community members, but we currently lack a framework that predicts how evolutionary responses of community members impact ecosystem properties including stability, resilience, susceptibility to invasion and regime shifts. We use Lotka-Volterra simulations to demonstrate how past events shape communities' collective behaviours. We show that ecological character displacement, operating strongest where species interact at highest densities:

i) Results in systems more resilient to invasion compared with communities with shorter shared histories, and that members of coevolved communities are better able to facilitate one another's invasion into other ecosystems (invasional meltdown).

ii) Provides systems with the potential to learn underlying environmental structure which, when correctly learned, results in greater system biomass and resilience.

iii) Enables ecosystems to learn multiple environmental states, and to store a distinct memory of each of these states (alternative stable states).

These complex system-level behaviours are not resultant from group selection processes, but arise only from selective pressures reinforcing correlations between community members.
Crucially, we recognise that this pattern of correlation learning is already well understood in connectionist models of learning, where simple reinforcement of connections produces networks with non-trivial collective behaviours.

# Ecological novelty may facilitate homoploid hybrid speciation in cichlid fish (52437)

**Oliver Martin Selz, Ole Seehausen.**

*Department of Fish Ecology and Evolution, Center for Ecology, Evolution and Biogeochemistry, EAWAG,; Aquatic Ecology and Evolution, Institute of Ecology and Evolution, University of Bern.*

Because homoploid hybrids are usually occurring within the range of the parental species, a central challenge to the concept of hybrid speciation is understanding how hybrids can persist in sympatry with their parental species. Persistence within the range of the parents is possible if the hybrid species inherit ecological traits that allow them to occupy a novel ecological niche, thereby allowing the lineage to escape competition from both parental species. Here, we investigate experimentally if novel feeding efficiencies can arise in synthetic first-generation hybrids that could make hybrids superior in ecological niches that neither of the parent species is adapted to.

We generated two first-generation hybrid crosses between different species of African cichlid fish. In feeding efficiency

experiments we determined the performance of the hybrids and their parental species on food types representing the niches of the parental species and on other “novel” food types that represent niches of other species of cichlids in African lakes. We found that hybridization can result in higher feeding

efficiency of the hybrids on novel food types when compared to either parent taxon. These results suggest that hybridization can generate novel phenotypic variation that might allow hybrids to escape competition from the parental species, thereby promoting ecological hybrid speciation.

# Beetles, Birds, Snakes & Flies: The Diversity of Sex Chromosomes and their Evolution (53361)

**Doris Bachtrog.**

In many species with separate sexes, gender is determined by heteromorphic sex chromosomes. Sex chromosomes have evolved independently in both plants and animals from ordinary chromosomes, but little is known about the evolutionary forces driving their differentiation. I will discuss how the study of diverse types of sex chromosomes, ranging
from beetles to birds, snakes and flies, has allowed us to make progress in understanding the
diverse mechanisms that drive the evolution of sex chromosomes.

Interactions Between A Master Regulator Of Sex Determination And Haploid
Sex Chromosomes In The Evolution Of Dimorphic Sexes (53315)

James Umen, Ayano Miyagi, Takashi Hamaji, Sa Geng.

Donald Danforth Plant Science Center.

Male and female sexes have evolved repeatedly in eukaryotes but the origins of dimorphic
sexes and their relationship to mating types in unicellular species are not understood.
Volvocine algae include isogamous species such as Chlamydomonas reinhardtii and
oogamous multicellular species such as Volvox carteri with sperm-producing males and egg-
producing females. We recently found that a single conserved mating locus (MT) gene in
volvocine algae—MID, which encodes a RWP-RK domain transcription factor—evolved
from its ancestral role in Chlamydomonas as a mating-type specifier, to become a determinant
of sperm and egg development in Volvox. Transgenic Volvox females expressing MID
produce functional sperm packets while transgenic male Volvox with RNAi-mediated
knockdowans of MID produce functional eggs or self-fertile hermaphrodites. Crosses with
sex-reversed strains uncouple sex determination from sex chromosome identity and reveal
roles for male and female mating locus genes in sexual development, gamete fitness and
reproductive success. Together these findings suggest the emergence of antagonistic
interactions between genes in the male and female sex chromosomes of Volvox. We have
begun to elucidate the genetic networks controlled by Chlamydomonas MID (CrMID) and
Volvox MID (VcMID) in order to understand how this transcription factor and its targets
evolved in the transition from mating types to sexes.

Baby sex chromosomes in the housefly (51681)

**Leo W Beukeboom**, Daniel Bopp, Ernst Wimmer, Louis van de Zande, Akash Sharma, Yanli Wu, Martijn Schenkel, Sander Visser, Ljubinka Francuski.

University of Groningen; University of Zurich; University of Goettingen; Univeristy of Novi Sad.

Sex chromosomes carry gender specific sex determining genes. Several stages can be
distinguished in the evolution of sex chromosomes, from origin, via molecular evolution as a
result of the sex determination function, to degeneration following recombination
suppression. We study the dynamic and polymorphic sex determination system of the
housefly, Musca domestica. The standard system is XX-XY with a male determiner (M) on
the Y chromosome, rendering it a male-determining chromosome. However, M-factors can
also be present on any of the five autosomes and as a result modify such chromosomes into
neo-sex (Y) chromosomes. In addition, autosome 4 can carry a dominant female determiner
(F), modifying it in a female determining sex chromosome, and a ZZ-ZW system. We provide
data on the nature of the female and male determining genes. Recent transposition events of
male determining genes over the genome has resulted in new sex chromosomes that are in the
very initial stages of differentiation (hence “baby” sex chromosomes). Here we present how
we use this unique system to test theories about sex chromosome evolution and to investigate
the genomic processes that act during the early stages of differentiation into male and female
determining sex chromosomes.

Wolbachia bacterial endosymbionts and the evolution of sex determination in
the isopod Armadillidium vulgare (51902)

Sébastien Leclercq, Julien Thézé, Isabelle Giraud, Mohamed Chebbi, Bouziane Moumen, Lise Ernenwein, Pierre Grève, Clément Gilbert, **Richard Cordaux**.

CNRS / Université de Poitiers.

In the isopod Armadillidium vulgare, sex determination (SD) follows female heterogamety (ZZ males and ZW females). However, many A. vulgare populations harbor maternally-inherited Wolbachia bacterial endosymbionts which can convert genetic males into phenotypic females, leading to populations with female-biased sex ratios. The W sex chromosome has been lost in lines infected by Wolbachia and all individuals are genetic males. Female sex is determined by Wolbachia infection of the A. vulgare individual, thereby shifting from chromosomal to cytoplasmic SD. Surprisingly, some A. vulgare lines exhibit sex ratio biases despite the lack of Wolbachia. In these lines, female individuals are genetic males carrying an unknown feminizing factor. To elucidate the genetic basis of female SD in these lines, we sequenced the genome of a female. We identified a large piece of the Wolbachia genome transferred to the A. vulgare nuclear genome. The transferred genomic fragment co-segregates perfectly with female sex in pedigrees. Our results indicate that SD in these A. vulgare lines is under control of nuclear gene(s) of bacterial origin. More generally, they emphasize that bacterial endosymbionts are powerful sources of evolutionary novelty, e.g. by driving shifts in SD mechanisms in their animal hosts. Funded by an ERC Grant to RC.

Why are there so many species with Y-autosome fusions? (51913)

**Jun Kitano**, Matthew Pennell, Mark Kirkpatrick, Sarah Otto, Jana Vamosi, Catherine Peichel.

National Institute of Genetics; University of Idaho; University of Texas, Austin; University of British Columbia; University of Calgary; Fred Hutchinson Cancer Research Center.
Sex chromosomes turn over rapidly in some taxonomic groups. One of the mechanisms causing the turnover of sex chromosome is a chromosomal fusion between a sex chromosome and an autosome. We estimate the rate at which fusions establish between sex chromosomes and autosomes through phylogenetic analyses of fishes and reptiles. Both the incidence among extant species and the establishment rate of Y-autosome fusions is much higher than for X-autosome, Z-autosome, or W-autosome fusions. Our theoretical analysis showed that the excess of Y-autosome fusions can be explained by (i) fixation of deleterious fusion by drift under the conditions of male-biased origination rates or male-biased variance in reproductive success, (ii) sexually antagonistic selection under the conditions of male-biased origination rates, and (iii) female meiotic drive against fusions. Because some of these evolutionary forces would also affect autosome-autosome fusions, further studies on the driving forces of sex chromosome-autosome fusions will give insight into the mechanisms causing not only sex chromosome turnover, but also karyotypic evolution.

# The Evolution of Epigenetic Inheritance (53348)

**Eva Jablonka.**

*The Cohn Institute for the History and Philosophy of Science and Ideas; The Sagol Tel-Aviv University.*

Epigenetic inheritance has many direct and indirect evolutionary effects, and it is likely that these are reflected in the evolved mechanisms underlying it. I therefore start with an overview of the effects of epigenetic inheritance on adaptive evolution, speciation, and the major evolutionary transitions. I then present existing models that explore the effects of ontogenetic epigenetic inheritance on evolutionary change, discuss different types of transgenerational epigenetic inheritance (somatic and gametic), and examine ideas about the environmental conditions that can lead to the evolution of trans-generational plasticity. I suggest that the diversity of selection regimes may explain the diversity of epigenetic mechanisms that are involved in trans-generational plasticity and metaplasticity.

# How does plasticity influence adaptive evolution? (53341)

**Cameron Ghalambor.**

*Colorado State University.*

A fundamental unresolved question in evolutionary biology is how patterns of plasticity observed within a generation influence evolutionary changes across generations. New environments, such as those encountered during colonization events or those generated by human activities, are likely to induce a range of both adaptive and non-adaptive plastic responses, thus providing an opportunity to test the relationship between initially plastic
responses and subsequent evolutionary change. We experimentally transplanted Trinidadian
guppies (Poecilia reticulata) adapted to a stream with cichlid predators to cichlid free streams,
and tested if plasticity in the source population predicted evolutionary change in the
transplanted populations. We measured a suite of traits, including gene expression, body
shape, growth rate, and metabolism. We found evidence for both adaptive and non-adaptive
plastic responses in the source population and rapid evolution of traits and their plasticity in
the experimental population. Traits exhibiting non-adaptive plasticity (i.e. a plastic response
in the opposite direction favored by selection) diverged from the source population more
rapidly. These results suggest traits exhibiting non-adaptive plasticity in new environments
are likely to experience stronger directional selection and evolve more rapidly compared to
traits exhibiting adaptive plasticity.

An evolutionary model of maternal effects (51650)

Rebecca Hoyle, Bram Kuijper.

University of Southampton; UCL.

Theory suggests that maternal effects can have substantial impact on the evolutionary process. However current models typically treat maternal effects as evolutionarily constant parameters. In order to glean insight into how maternal effects themselves are shaped by evolution, we present a quantitative genetics model that captures the interacting evolutionary dynamics of both maternal effects and within-generation phenotypic plasticity. In constant environments, we find that maternal effects evolve to slightly negative values that reduce phenotypic variance in the population. By contrast, in the wake of an extreme environmental shift, they evolve to large positive values over ten to a hundred generations. These transient positive values allow offspring to rapidly adopt beneficial phenotypes that are closer to the new optimum. Once this new optimum has been reached through within-generation plasticity and genetic assimilation, maternal effects drift back towards negative values where they eventually settle. Lastly, in cyclically fluctuating (e.g. seasonal) environments, maternal effects often evolve to positive values when fluctuations are slow, whereas negative maternal effects dominate for faster cycles. We find that cyclical environments favour weak maternal effects unless selection on the overall phenotype is strong and the efficacy of within-generation phenotypic plasticity is constrained through costs or informational timelags.

Paternal heat exposure causes immediate and inherited epigenetic response in
Wild guinea pigs (51721)

**Alexandra Weyrich**, Dorina Lenz, Marie Jeschek, Tzu Hung Chung, Felix Heeger, Kathrin Rübensam, Frank Goeritz, Katrina Jewgenow, Jorns Fickel.
Epigenetic modifications, of which DNA methylation is the best studied one, are a mechanism
to convey environmental information through generations via parental germ lines. The
majority of studies have focused on the maternal transmission of epigenetic information to the
offspring, whereas the paternal role in transgenerational transmission has received little
attention. Here we show that exposure to a temporally increase in ambient temperature led to
changes in DNA methylation patterns in exposed males and were transmitted to their male
offspring. Five F0 adult male guinea pigs, a phenotypically and genetically heterogeneous
mammal species, were exposed to an increase in ambient temperature for two months.
Reduced representation bisulfite sequencing revealed differentially methylated regions
(DMRs) in liver samples of F0 fathers before and after heat treatment, as well as in liver and
testes of F1 sons sired before and after heat treatment. Since testicular methylation changes
imply transmission to the F2 generation, exposure of fathers to increased temperature resulted
in rapid and heritable epigenetic modifications that were transmitted paternally. In the context
of climate change this mechanism is increasingly relevant for the survival of exposed
populations with rising global temperatures.

Genome methylation patterns across castes and generations in a parasitoid
wasp (51740)

Roei Shaham, **Tamar Keasar**, Rachel Ben Shlomo.

University of Haifa - Oranim.

Environmental influences play a crucial role in shaping phenotypes within and across
generations. In vertebrates, these influences often involve epigenetic modification of gene
expression through DNA methylation. Modifications of methylation patterns also mediate
caste and task allocation in eusocial insects. However, the effects of parental environment on
DNA methylation in offspring are yet unknown in insects. We looked for within- and
between-generation variability in methylation in the polyembryonic parasitoid wasp
Copidosoma koehleri, which also features a unique simple caste system.

To study within-generation effects, we tested for methylation differences between
reproductive and soldier clone-member larvae. To explore between-generation effects, we
exposed larvae to either high or low rearing densities. We compared methylation in their
offspring at three developmental stages (larvae, pupae and adults). Methylation rates and
patterns were characterized using the methylation-sensitive amplified fragments length
polymorphism (MS-AFLP) method.

DNA methylation patterns differed significantly between soldier and reproductive larvae,
although frequencies of methylated fragments were similar across castes (~20%). Parental
rearing density did not affect methylation rates and patterns in their offspring in any of the
developmental stages. Thus, DNA methylation is associated with within-generation (caste)
phenotypic variation, but we found no evidence for its involvement in trans-generational
epigenetic effects.
# Region-specific selection on floral signals in a terrestrial orchid (52200)

**Karin Gross**, Florian P Schiestl.

*University of Zürich.*

Geographically structured phenotypic selection can lead to adaptive divergence. In flowering plants, the link between selection and trait divergence has been shown for flower morphology, but not yet for floral signals, despite their importance for pollinator attraction. In this study, we measured phenotypic selection on display size, floral color, and floral scent in four lowland and four mountain populations of the nectar-rewarding orchid Gymnadenia odoratissima. We also quantified differences in these traits and in pollinator-community composition. Our results show positive selection on display size and positive, negative, or absence of selection on different scent compounds. Selection on the main scent compounds was consistently stronger in the lowlands than the mountains in two years, and lowland plants emitted more of most of these compounds. Pollinator-community also differed among regions. We also found an association between population differences in some scent compounds and the respective differences in selection on them. Moreover, selection on floral scent was more variable than selection on display size, and scent emission was also more variable than display size. Overall, our study is the first to document consistent regional differences in selection on floral scent, and suggests this selection pattern contributes to population divergence in floral chemical signaling.

# Selection and real-time evolution of floral traits in plants with different pollinators (52209)

Daniel Gervasi, Florian P Schiestl.

*University of Zürich.*

Selection mediated through pollinators plays a key role in floral adaptation and reproductive isolation in plants. The aim of this study was to investigate pollinator-driven selection by experimentally changing pollinator environments. Specifically we investigate the effects of different pollinators on the evolution of floral traits and plant reproductive success. We use Brassica rapa (Wisconsin rapid cycling) as model plant and the bumblebee, Bombus terrestris, and the hoverfly, Episyrphus balteatus as pollinators. In our study we found that bumblebees and hoverflies differ in the selection they impose on floral traits. The strength of selection on the floral traits also varies significantly between the two pollinators. We observed strong positive selection on plant height and flower number in bumblebees while hoverflies imposed no selection on these traits. In terms of evolutionary response we observed in bumblebee-visited plants an increase in plant height and flower number. Additionally, bumblebee pollinated plants had a significantly higher reproductive success than hoverfly pollinated
plants. After 7 generations hoverfly-pollinated plants showed a significant increase in reproductive success indicating adaptations to this type of pollinators have evolved. This study thus shows for the first time the effects of changing pollinators on plant evolution in an experimental approach over several generations.

## Over-dominance and adaptive gene duplications (52262)

**Pascal Milesi**, Mylène Weill, Pierrick Labbé.

*Institut des sciences de l'évolution; CNRS; Université de Montpellier.*

For 40+ years, organophosphorus insecticides (OPs) have been used to control <i>Culex pipiens</i> mosquito populations. A punctual mutation of the <i>ace-1</i> gene conferring resistance was rapidly selected for, despite the strong selective cost it induces. As a consequence, selection is environment-dependent: susceptible homozygotes are selected in the untreated areas, whereas resistant homozygotes are selected in the treated ones. Nevertheless, with intermediate selection intensities, e.g. in a fluctuating or structured environment, heterozygotes with intermediate advantage and cost could be the fittest, i.e. marginal over-dominance.

In the last 20 years, gene duplications at the <i>ace-1</i> locus invaded <i>C. pipiens</i> natural populations. They associate on a same chromosome a susceptible and a resistant copy of <i>ace-1</i>, and recent study showed that they confer a phenotype similar to standard heterozygotes. It was thus suggested that these duplications were selected because they alleviate the heterozygote segregation cost, thereby allowing fixation of the over-dominant phenotype.

We tested this over-dominance hypothesis and its relation to insecticide dose, i.e. selective pressure intensity. Our results show that selective pressure heterogeneity can play a key role in the emergence of adaptive gene duplications.

## Temporal fluctuation in the phenotypic optimum of laying date in a wild Blue tit population (52355)

**Pascal Marrot**, Dany Garant, Charmantier Anne.

*Centre d'Ecologie Fonctionnelle et Evolutive; Université de Sherbrooke.*

Understanding the role of temporal fluctuations in natural selection in maintaining phenotypic variance in natural populations is central in evolutionary ecology. Temporal fluctuation of natural selection is generally estimated by comparing annual selection gradients, which represent the slope of the fitness landscape. However, such variation in selection gradients does not necessarily reflect variation in the fitness-trait relationship, but can be caused by changes in the extent of phenotypic variance present under genetic drift. In this context, it
could be more informative to investigate temporal variation in the phenotypic optimum on the fitness landscape rather than in selection gradients. Here, we apply a model recently developed by Chevin & Haller (2014) to explore temporal variation and temporal autocorrelation in the phenotypic optimum for laying date using a 23 year blue tit (Cyanistes caeruleus) data set. Our results show that the phenotypic optimum varied between years and followed a negative temporal autocorrelation pattern. This result suggest that selection pressures within a given year cannot be predicted from selection pressures observed during the previous year, which emphasizes the variability of selection pressures across years. Moreover, this model allows us to investigate the relationship between temporal variation in phenotypic optimum and environmental covariables such as spring temperature or precipitation.

# THERE IS MORE TO POLLINATOR-MEDIATED SELECTION THAN POLLEN LIMITATION: INTERACTION INTENSITY VERSUS FUNCTIONAL SIGNIFICANCE (52367)

Nina Sletvold, **Jon Ågren**.

*Uppsala University.*

Spatial variation in pollinator-mediated selection (Δβpoll) is a major driver of floral evolution, but we lack a quantitative understanding of its link to pollen limitation and net selection on floral traits. To determine whether Δβpoll is positively related to pollen limitation and whether differences in the magnitude of Δβpoll can explain spatio-temporal variation in net selection, we quantified Δβpoll on floral traits for 2-5 years in two populations each of two orchid species differing in pollen limitation. In both species, Δβpoll varied among years and populations, and spatio-temporal variation in Δβpoll explained much of the variation in net selection. Selection was consistently stronger and the proportion that was pollinator-mediated was higher in the severely pollen-limited deceptive species than in the rewarding species. Within species, variation in pollen limitation could not explain variation in Δβpoll for any trait, indicating that factors influencing the functional relationship between trait variation and pollination success govern a major part of the observed variation in Δβpoll. Separating the effects of variation in mean interaction intensity and in the functional significance of traits will be necessary to understand spatio-temporal variation in selection exerted by the biotic environment.

# Local adaptation is prevented along patchy ecological gradients (52510)

**Jon Bridle**, Roger Butlin.

*University of Bristol; University of Sheffield.*
Population genetic models of evolution along spatial gradients in selection cannot explain why species have finite geographical distributions and narrow niches. Unless gradients in population density are imposed by locally varying carrying capacity, gene flow helps rather than hinders local adaptation, provided the standing genetic variance it generates does not impose too much of a demographic cost. Continuous evolutionary models therefore either generate extinction or adaptation everywhere, instead of the finite distributions that are ubiquitous in nature and that define biological communities. We use individual-based simulations to explore how non-linear ecological gradients affect local adaptation by varying gene flow and overall carrying capacity along: (1) a steepening ecological gradient and (2) a linear ecological gradient with a flat centre of variable width. We find that adaptation is prevented along non-linear gradients because populations within flat regions escape the demographic load generated by gene flow elsewhere. These flat regions can prevent adaptation even when remarkably narrow relative to mean dispersal. At the same time however, patchy gradients make population establishment easier, and prevent global extinction. We discuss our results in the light of our empirical work on evolutionary responses to climate change in the UK butterfly Aricia agestis.

## Genomics of local adaptation in the face of high gene flow (52868)

**Outi Savolainen**, Timo Knürr, Sonja Kujala, Jaakko Tyrmi, Katri Kärkkäinen, Tanja Pyhäjärvi.

*University of Oulu; Luke Natural Resources Center Finland.*

Populations of many species with high gene flow have little differentiation across much of the genome, but can still be highly differentiated for phenotypic traits related to local adaptation. Scots pine and many other forest trees show this kind of patterns of variation. In common garden experiments, northern Scots pine seedlings set bud much earlier than southern ones, an important adaptive difference. Analysing selection in common garden tests at different latitudes, we found a cline in the optima over latitudes, and within individual populations, strong stabilizing selection on the timing of bud set. The strength of selection varied between sites at different latitudes. Further, we examined clines of nucleotide variation across European wide sampling, using limited SNP genotyping and exome sequencing. The results are compared to predictions of models of clinal selection.

## Variation and selection of genes controlling ecologically important traits in nature (53317)

**Thomas Mitchell-Olds**, Nadeesha Perera, Julius Mojica, Lauren Carley, C. Olson-Manning, J. Anderson, C-R Lee.

*Duke University; University of Chicago; University of Georgia; Gregor Mendel Institute.*
Although many studies provide examples of evolutionary processes such as balancing selection or deleterious polymorphism, the relative importance of these processes for phenotypic variation is unclear. To understand the evolutionary forces that influence complex trait variation in a wild relative of Arabidopsis, we cloned an ecologically important QTL in natural populations and measured the fitness of alleles in the populations where they evolved. Ecological measurements of selection indicate that this polymorphism is influenced by spatially heterogeneous natural selection, with changes in rank fitness across environments. Next, we examined the relationship between flux and protein polymorphism in this pathway, showing that flux control is focused in the first enzymatic step, encoded by a gene experiencing selective diversification in several related species. Finally, to identify the genes responsible for ecologically important trait variation in nature, we are conducting a Genome-Wide Association Study (GWAS) on a panel of reference genotypes from 500 populations across the species range. For these accessions we combine data from genome-wide resequencing and genotyping by sequencing, as well as trait variation for defensive chemistry, resistance to multiple herbivores, flowering time, and complex traits in lab and field. Implications for ecological genomics will be discussed.

**Genetic variance associated with overwintering adaptation in a butterfly.**
**(51641)**

**Peter Pruisscher**, Christopher Wheat, Karl Gotthard.

*Stockholm University.*

Diapause is a pre-programmed state of arrested development in insects that is a crucial part of life cycle regulation. Many species induce diapause depending upon environmental conditions, allowing for either continuous development during optimal conditions (summer) or diapause (overwintering). This adaptation to seasonal stress is primarily triggered by photoperiod and temperature. The propensity of populations to enter diapause in response to a given light/dark regime shows strong adaptive clines along environmental gradients. Diapause is a complex multi-locus trait incorporating cold-tolerance, immunity and growth patterns, suggesting that many loci are likely involved. Here we scan the genome of divergent populations of the Speckled Wood butterfly Pararge aegeria, as well as data from F1 and F2 crosses, to investigate the genetic mechanisms underlying diapause. Our analysis identifies a range of high quality candidate loci known to be involved in diapause in other species [e.g. clock genes, heat-shock proteins]. Furthermore, prime candidates, such as the gene Timeless, show nonsynonymous substitutions fixed between the divergent populations.

**Experimental evidence for mitochondrial genomic adaptation to climate**
**(51932)**

**M. Florencia Camus**, Carla M. Sgrò, Jonci N. Wolff, Damian K. Dowling.
Monash University.

Mitochondria are key components of cellular metabolic processing, providing most of the
cellular energy required for survival. It was traditionally thought that the mitochondrial
genome exhibits very limited capacity to respond adaptively to natural selection. However,
thermal sensitivity of mitochondrial functioning, coupled with the observation that
mitochondrial haplotype frequencies tend to associate with latitude or altitude, suggests that
thermal selection may play a role in shaping the molecular architecture of the mitochondrial
DNA. Here, we present experimental support for this contention. We describe two major
mitochondrial haplotypes in Drosophila melanogaster, which exhibit opposing patterns of
clinal variation along the Australian eastern seaboard and are delineated by 15 synonymous
SNPs. We extracted each of these haplotypes from two opposing populations and introgressed
them into a single isogenic nuclear background. After assaying each population for thermal
tolerance we found the northern haplotype confers greater heat resistance. The underlying
SNPs involved in this phenotypic response lie unambiguously in the mitochondrial genome,
and are hypothesized to affect the level of codon bias. Thus, we have uncovered a new-found
role for SNPs that were previously considered to be completely non-functional, inside a
genome that was likewise traditionally considered to be devoid of functional segregating
allelic variation.

Origin, history and local adaptation of the recent polyploid Capsella bursa-pastoris (51946)

Martin Lascoux, Amandine Cornille, Adriana Salcedo, Dmytro Kryvokhyzha, Karl Holm, Ulf Lagercrantz, Sylvain Glémin, Stephen Wright.

Uppsala University; University of Toronto.

It took more than 80 years, since George Shull started to use Capsella bursa-pastoris as a
model species for the study of Mendelian genetics, to decipher the origin of the species. It
took as long to start to unravel its demographic history and to estimate the nature and extent
of the natural selection it went through as it colonized the world. The analysis of full genomes
shows that Capsella bursa-pastoris is an allotetraploid of the self-incompatible C. grandiflora
and the self-compatible C. orientalis. It also indicates that polyploidization was accompanied
by relaxed selection but rather limited gene loss. As shown by the genotyping of 260
accessions from Europe, the Middle East and Asia, the species is today made up of clearly
delineated genetic clusters corresponding to these three areas. The species likely originate in
Western Eurasia from which it later on spread eastwards. Clear differences in gene expression
were detected among 24 accessions originating from these three clusters but a contrast
analysis also suggest that those differences may simply reflect the demographic history of the
species and may not be adaptive. Finally, three common garden experiments of the 260
accessions located in Uppsala, Toronto and Guangzhou are currently under analysis.
# The genomics of avian breeding time – an ecologically relevant trait for adaptation to climate change (51982)

**Phillip Gienapp**, Mario P.L. Calus, Veronika N. Laine, Kees van Oers, Martien A.M. Groenen, Jon Slate, Marcel E. Visser.

*Department of Animal Ecology, Netherlands Institute of Ecology; Animal Breeding and Genomics Centre, Wageningen UR; Department of Animal and Plant Sciences, University of Sheffield.*

Climate change has led to selection on phenological traits such as avian seasonal breeding time and hence evolutionary rescue will be necessary to ensure population persistence in the long-term. Numerous quantitative genetic studies in wild populations have shown that avian seasonal breeding time is heritable, yet no study could show the expected evolutionary change. One possible explanation for this ‘evolutionary stasis’ is that heritability estimates are inflated by environmental conditions shared among relatives. A good understanding of the genetics of avian breeding time is thus crucial to predict whether this trait can respond to selection. We here explored the genomic basis of avian seasonal breeding time in a wild bird species, the great tit, using our recently assembled and annotated whole genome sequence and high-density SNP-chip of this bird species. We genotyped 2000 individuals with known egg-laying dates from our long-term study population on a 675k SNP-chip and identified genomic regions related to breeding time using both QTL-mapping and by quantifying locus-specific allele-substitution effects using a genomic-breeding approach.

# Defence heterogeneity under the double-edged sword of mammalian immunity (53314)

**Andrea L. Graham.**

*Princeton University.*

To mitigate the effects of infection on fitness, hosts must minimize the costs of both parasitism and defence. This may entail clearing parasites, but it may be even more important for hosts to repair tissue damage caused by parasites and by immune effectors. Hosts may also need to maintain physiological homeostasis while mitigating energetic costs. Striking an optimal balance amongst these competing physiological demands is a dynamic problem. For example, the optimal strategy may vary with age, condition, risk of parasite exposure and/or availability of resources in the environment. To what extent can mammalian hosts match their defensive stance to environment? Must competing demands be met simultaneously or are sequential solutions possible – e.g., to kill parasites rapidly then shift to a damage- and energy-reduction strategy later, or, conversely, to tolerate parasites up to a threshold and resist them thereafter? Indeed, how much of defence heterogeneity, including varied susceptibility to autoimmune disease, can be understood in light of this multivariate physiology? I will address these questions using immunological, nutritional and histopathological evidence from both wild mammals and human cohorts.
# Balancing selection and convergent evolution in an antimicrobial peptide (53316)

**Brian P. Lazzaro**, Robert L. Unckless, Virginia M. Howick.

*Cornell University, USA.*

Conventional thinking has been that antibacterial peptides (AMPs) are functionally redundant and evolutionarily dispensable at the individual gene level. In Drosophila, this inference has been drawn from observations that antibacterial peptide genes show low rates of amino acid divergence between species and high rates of genomic duplication and deletion, and that genetic variation in individual AMP genes makes little or no contribution to organism-level defense phenotypes. However, we identified a serine/arginine polymorphism in the Dipticin A gene of Drosophila melanogaster that is highly predictive of resistance to specific bacterial infections. The same amino acid polymorphism is segregating in the Dipticin A gene of the sister species D. simulans, with equivalent phenotypic effect and having arisen convergently by independent mutation of the homologous codon. Examination of the larger Drosophila phylogeny reveals that the arginine mutation has arisen independently at least 5 times in the genus. These observation prompted us to revisit the molecular evolution of other antibacterial peptide genes and we find that molecular convergence and shared interspecific polymorphism are surprisingly common. We additionally have found multiple loss-of-function mutations, which cause high susceptibility to infection in D. melanogaster and D. simulans. We have reevaluated the previously supposed mode of evolution of Dipticin and other antibacterial peptide genes, and now favor the hypothesis that AMP genes evolve under a model where the selection pressure favoring alternative amino acid states fluctuates over time and space. The frequent incidence of loss-of-function alleles in nature suggests that AMP function in immune defense is balanced by deleterious consequences in the absence of infection, and serial pseudogenization and duplication-subfunctionalization may explain the rapid gene family dynamics. Since previous screens for molecular adaptation have explicitly tested for adaptive divergence, these would have failed to detect convergent or balanced mutations.

# Genome wide analysis of selection in immune genes within and among butterfly populations (51667)

**Naomi Keehnen**, Chris Wheat.

*Stockholm University.*

Insects are one of the most diverse clades of life on earth. Located in nearly every corner of Earth, they are exposed to a wide variety of pathogens. As populations adapt to their local environment some modifications to their immune system are expected to occur. While the genes encoding for immune responses have been identified and studied in several insect
species, little work has focused upon non-model species originating from natural populations. Furthermore, it is unknown which part of the immune defense modules (recognition, signaling, and the effectors) shows most genetic variation within and between species. Here we focus upon the ecological model species, the Green Veined White (Pieris napi) and Speckled Wood (Parage aegeria). They are common and widespread, with limited gene flow between populations. We have identified many of the immune genes in both butterfly genomes using orthologous blast searches and RNA-Seq analysis of individuals infected with either gram-negative (E. coli) or gram positive bacteria (M. luteus). Genomic scans of these immune genes indicate signatures of local adaptation and reveal significant differences in diversity among the immune defense modules. These findings could explain the observed variation in immune responses within and between butterfly species.

## Functional variation at innate immune loci in the Seychelles warbler (51755)

**Danielle Gilroy.**

*University of East Anglia.*

Understanding the relative roles of different evolutionary forces in shaping genetic variation within a population is a key focus in evolutionary biology. Moreover, understanding the levels and distribution of functional genetic variation in bottlenecked populations has great importance to conservation. The Seychelles warbler (Acrocephalus sechellensis) is an endemic passerine that went through a severe population bottleneck in its recent past and we investigated whether variation has been maintained within two innate gene groups, avian beta-defensins (AvBDs) and toll-like receptor genes (TLRs). We also examine these genes in several other Acrocephalus species, revealing very different selection regimes for the two gene groups within the Seychelles warbler and across the genus. All six AvBD loci were monomorphic in the contemporary population of Seychelles warbler and five out of seven TLR loci were polymorphic. By using population genetic statistical tests and simulation studies, we show that founder effects have reduced levels of variation at TLRs, but balancing selection has indeed maintained some functional variation at five of the loci. Furthermore, a cohort analysis of TLR15, examined allele-specific associations with survival and malaria infection that enabled us to better understand whether pathogen-mediated selection could potentially be the underlying balancing selective force in this population.

## Genetics of natural variation of Daphnia magna resistance to a bacterial pathogen (51867)

**Gilberto Bento, Jarkko Routtu, Yann Bourgeois, Dieter Ebert.**

*University of Basel.*
Daphnia magna is a model for ecology and evolution, in particular, for host-pathogen coevolution. D. magna is infected by the bacterium Pateuria ramosa with severe deleterious fitness consequences. We investigate the D. magna-P. ramosa system for the genetic and molecular basis of natural variation in host resistance. Specificity in genotype-to-genotype interactions was previously reported. In addition, using a D. magna F2 panel, it was found that one QTL (locus A) explains variation in host resistance to one P. ramosa genotype, C19. We found that one exceptionally large insertion-deletion polymorphism (~50 kb) underlies locus A. Next, we found that variation in locus A is associated to a combination of resistance to P. ramosa C1 and susceptibility to C19 throughout a genetically and phenotypically diverse D. magna meta-population. Our results are consistent with the D. magna-P. ramosa relationship evolving by negative frequency dependent selection. We are currently investigating which specific genes located in locus A are responsible for the phenotypes observed. For that we are using a technique of directed genome editing, CRISPR/Cas9, that was recently established for Daphnia magna. We expect to knockdown candidate genes, and to establish functional relationship between gene and host resistance.

## Experimental evolution of host specificity by comparing single and multiple infections (51918)

Rebecca D Schulte, Joy Bose, Michaela H Kloesener.

*University Osnabrueck.*

Host-parasite coevolution is considered as one of the main drivers of evolution since it requires continuous adaptation and counter-adaptation of both antagonists. However, host-adaptation towards specific parasites often entails a loss of adaptation towards other parasites. Evolution of host defence should thus depend on the parasites they encounter and coevolve with, and should result in diversification between populations. We studied adaptation of the nematode Caenorhabditis elegans to its microparasite Bacillus thuringiensis using experimental evolution. Specifically, hosts coevolved either with one parasite strain or with a mix of two strains. We found that hosts evolving with one parasite strain evolve defence against it, but loose defence against an unknown parasite strain, i.e. they evolve specificity. Hosts evolving with two strains simultaneously show intermediate levels of survival when encountering only one strain, but survive better with a combination of both strains compared to hosts which evolved with one strain only. This indicates adaptation trade-offs, i.e. hosts cannot be well adapted to two strains at the same time. Our results show that parasites select for diversification between as well as for diversification within host populations depending on the parasite communities they encounter and thus support the role of parasites for diversification and speciation.

## The thin line between conformational freedom and anarchy - negative epistasis and evolvability in TEM-1 beta-lactamase (53309)
Dan Tawfik.

Weizmann Institute of Science.

Epistasis is a key factor in evolution, since it determines which combinations of alleles provide adaptive solutions and which mutational pathways towards these solutions are accessible by natural selection. There is growing evidence for the pervasiveness of sign epistasis, particularly in protein evolution, yet its molecular basis remains poorly understood. I will describe the structural basis of reciprocal sign epistasis between two adaptive mutations in the antibiotic-resistance enzyme TEM-1 b-lactamase, G238S and R164S. Separated by 10Å, these mutations initiate two trajectories towards increased resistance. Both mutations allow the enzyme's active-site to adopt alternative conformations and accommodate the third-generation antibiotic cefotaxime. However, whereas G238S induces discrete conformations, R164S causes local disorder. When combined, the mutations in 238 and 164 induce local disorder whereby nonproductive conformations that perturb the enzyme's catalytic pre-organization dominate. This local disorder is not restored by stabilizing, global suppressor mutations and thus leads to an evolutionary cul-de-sac.

# How do proteins evolve? Simulating evolution with in silico models of protein thermodynamics (53331)

Richard A. Goldstein.

University College London.

As with the blind men and the elephant, researchers with various perspectives have developed different conceptual models for how proteins evolve. Evolutionary biologists motivated by Fisher's geometric model have emphasised how conservative mutations would be more likely to be accepted than more radical changes, just as how adjusting the fine focus of a microscope is more likely to yield an improvement than adjusting the course focus. Scientists with more of a structural biology background describe the match between location in the protein and the suitability of any amino acid for such a location - mutations to more suitable amino acids, including radical changes, should be accepted at a higher rate. There has been a growing understanding that a protein is an integrated system so that many of the selective constraints are properties of the entire protein such as structure, stability, solubility, and resistance to aggregation. In this perspective, the selection acting on one site is always in the context of the amino acids found in other sites. And as with the tangled bank described by Darwin, there will be a complex network of feedback loops; substitutions at one focal position will affect the selection acting on other sites; the corresponding substitutions at these other sites will, in turn, influence the selection acting on the focal position. One aspect of this is the so-called 'Stokes Shift', where the rest of a protein adopts itself to the new amino acid resident at a given site so that, as long as that amino acid remains at the site, it becomes increasingly suitable for that position. These contrasting perspectives suggest different approaches to understanding and interpreting molecular evolution. We can simulate protein evolution in silico over long periods of evolutionary time. We can use these simulations to evaluate how well these
different models capture the evolutionary process, the types of errors that might result from an
inappropriate model, and how these approaches can be reconciled.

Tandem repeats in coding region constitute another mechanism of adaptive
radiation in cichlid fish (51770)

Langyu Gu, Walter Salzburger.

*Zoological Institute, University of Basel, Basel 4051, Switzerland.*

Convergent evolution provides an ideal scenario for testing the role of natural and sexual selection in adaptive radiations. However, to what extent the same genes and genetic pathways or different ones contribute to convergent phenotypes is still unclear. Cichlid fishes, which feature mutliple convergent phenotypes, provide an ideal model system to answer the questions why certain key traits are important in some lineages but not in others, and how these phenotypes evolved and are maintained developmentally. Egg-dummies are an evolutionary key innovation of East African cichlids that have been suggested to contribute to their evolutionary success. Using comparative transcriptomic and genomic analyses, we identified an egg-dummy candidate gene showing cichlid-specific tandem repeats in its coding region, which represent a a functional domain and are under positive selection. More interestingly, the polymorphism of these repeats is associated with species richness. We hypothesize that the repeats enlarge the available binding properties of this gene, constituting yet another mechanism of adaptive divergence in cichlids.

Correlated substitutions are rare under molecular coevolution (52722)

David Talavera, Simon Lovell, **Simon Whelan**.

*University of Manchester; Uppsala University.*

Molecular coevolution occurs when substitutions at one site influence evolutionary change at other sites. It is commonly assumed that coevolution results in correlated amino acid substitutions at groups of sites that are close together in the protein structure, and identifying such sites would be useful in (e.g.) de novo protein structure prediction. Many methods have been developed to detect molecular coevolution either directly, through phylogenetic models, or indirectly by identifying covariation, a commonly assumed outcome of coevolution. Despite decades of research these methods still have low power, even with massive alignments of 10000s of sequences.

This study examines the consequences of coevolution at the sequence level and how it affects covariation. Our theoretical results predict that all methods for detecting molecular coevolution will have extremely limited power because in order to have enough correlated substitutions to detect coevolution the strength of selection reduces evolutionary rate so much
that very few substitutions are likely to occur. These results are empirically confirmed by studying the performance of covariation methods, where true positive predictions of physical proximity are not associated with correlated mutations, but instead tend to occur from the detection of low rate sites within occur predominately in the protein core.

# Disease-related mutations in proteins: a study of dynamically correlated networks and coevolved residue clusters (52814)

**Yasaman Karami**, Serge Amselem, Elodie Laine, Alessandra Carbone.

Université Pierre et Marie Curie, UMR 7238, Equipe de Génomique Analytique, Paris, France; CNRS, UMR 7238, Laboratoire de Biologie Computationnelle et Quantitative, Paris, France; Sorbonne Universités, UPMC Univ Paris 06, ICS, Paris, France; Service de Génétique et d'Embryologie Médicales, UMR S933 INSERM / UPMC, Hôpital Armand-Trousseau; Institut Universitaire de France, Paris, France.

Point mutations can induce effects at distant protein sites, thereby provoking diseases. Networks of dynamically correlated residues play a crucial role in propagating such perturbation signals. These residues are also expected to display high degrees of conservation and/or coevolution. We performed a consensus analysis of dynamically correlated and coevolved residue networks in three archetypal proteins. Dynamically correlated residues were detected from all-atom molecular dynamics simulations and grouped into: Communication Pathways and Independent Dynamic Segments (1), which represent two complementary media for allosteric communication. Coevolved residues were detected by sequence analysis using BIS (2) and clustered with CLAG (3). Results reveal a significant overlap between clusters of coevolution and networks of dynamical correlation. We examined the impact of two disease-related mutations on the allosteric communication of growth hormone. The comparison of wild-type and mutant showed a rewiring of Communication Pathways linking coevolved residues. Characterizing the dynamical behavior of proteins provides a means for physical understanding of coevolution signals. Understanding the role of disease-related mutations on the link between coevolution and dynamical correlation can help decipher the molecular mechanisms of mutation-induced allosteric deregulation.

1E. Laine, et al., PLoS CB (2012).

2L. Dib, A. Carbone, PLoS ONE (2012).

3L. Dib, A. Carbone, BMC Bioinformatics (2012).

# Complex phylogeny of aminoacyl-tRNA synthetases (52521)

**Alex Popinga**, Remco Bouckaert, Peter Wills.
Department of Computer Science, University of Auckland; Allan Wilson Centre for Molecular Ecology and Evolution; Machine Learning Group, University of Waikato; Department of Physics, University of Auckland.

All aminoacyl-tRNA synthetases (aaRSs), of all specificities from all known organisms, fall into two main classes. Each class has a core structure that has been highly conserved since the origin of life 3.8 billion years ago. The aaRSs have evolved from the simplest (core) structures, which provided the basic functional requirements for interpreting a loose binary code, into the complex present day structures that are capable of interpreting the highly specific 61-codon to 20-amino acid universal genetic code. Throughout this process, thermodynamic instabilities drove bifurcation events in the aaRS phylogeny, expanding the amino acid alphabet by one binary digit at each bifurcation. Therefore, in order to analyse the cophylogenies of Class I and Class II aaRSs before the LUCA event, it is necessary to consider epochs in which there were fewer than 20 classes of distinguishable amino acids, invalidating the use of 20 x 20 substitution matrices throughout the phylogenetic inference. To tackle this problem, we have developed an extension of BEAST, using matrices of reduced 2 ≤ n ≤ 20 dimensions for each pre-organismal epoch. Results from the phylogenetic analysis are used in complement with empirical structural data to examine the transitions of specificity in these self-constructing interpreters.

Session 1 TUE POL D 33

# Evolution and development of floral signals influencing pollinator behaviour
(51809)

**Beverley Glover.**

*University of Cambridge.*

The morphology of flowers influences pollinator behaviour in many different ways. We are interested in how changes in flower symmetry, shape, size, colour and texture influence which pollinators visit a plant and how they interact with it. These interactions can lead to reproductive isolation and speciation. Our recent work has focused on a rare example of sexual mimicry outside the orchids, the South African daisy Gorteria diffusa. I will describe our analysis of the fly-mimicking petal spots of this species, focusing on their development and their variability, and discuss how this morphological variability relates to pollinator behaviour.

Session 1 TUE POL D 33

# Genetic Parallelism in Flower Color Evolution (51847)

**Mark Rausher.**

*Duke University.*
A recurring question in evolutionary biology is whether parallel genetic evolution underlies parallel phenotypic evolution. Most studies addressing this question, however, are based on only two or three species, which limits conclusions that may be drawn. Using a larger sample of species allows one to perform statistical analyses to determine whether the frequency spectrum of genetic changes differs from random expectations. Using studies on the evolution of floral pigments, I apply this type of analysis to demonstrate genetic parallelism. In addition, I show how information about mutation spectra can be used to determine whether genetic parallelism is due to differences in mutation frequency or in the magnitude of deleterious pleiotropy.

# The molecular basis of genic ecological speciation in sexually deceptive orchids (51586)

Philipp Schlüter, Khalid Sedeek, Shuqing Xu, John Shanklin, Salvatore Cozzolino, Florian Schiestl.

*University of Zurich, Switzerland; Max Planck Institute for Chemical Ecology, Germany; Brookhaven National Laboratory, USA; University of Naples Federico II, Italy.*

High pollinator specificity and the potential for simple genetic changes to affect pseudo-pheromone blends, and thus pollination, make sexually deceptive Ophrys orchids an interesting study system for ecological speciation. A survey of different reproductive barriers revealed that only premating reproductive isolation (RI), particularly pollinator-mediated RI, has evolved between sympatric and co-flowering species. Genotyping by sequencing revealed shared polymorphism throughout the Ophrys genome. Genome scans for FST outliers identified few markers that were highly differentiated between species, identifying genes involved in floral odour production. Chemical mimicry of insect pheromones is achieved by the synthesis of alkenes with different double-bond positions, which are primarily controlled by the action of two acyl-ACP desaturase-encoding genes, SAD2 and SAD5. These loci originated by gene duplications from an ancestral, housekeeping-desaturase-like gene, and have undergone changes in both gene expression and protein function. An amino acid change during the evolution of SAD5 may have altered its enzymatic activity and released the protein from pleiotropic constraint, allowing it to carry out its specific function in alkene biosynthesis. Evolutionary modelling of this two-locus architecture of RI reveals the effect sizes of the two desaturases to be unequal and predicts potential and constraints for rapid pollinator-driven speciation in sympatry.

# Gene flow and the genetic architecture of speciation revealed by 1043 stick-insect genomes (51629)

Patrik Nosil.
Genome variation during the often-complex speciation process is affected by numerous factors, and can affect the likelihood of evolutionary diversification. Disentangling the processes driving patterns of genome variation is challenging, because different processes can generate similar patterns. In this talk, I will combine data from whole genome re-sequencing of natural and experimentally transplanted populations, genome wide association mapping, and theoretical modeling to test the processes driving genome divergence during ecological speciation in Timema stick insects. The results indicate that even the early stages of speciation can involve numerous genomic regions affected, either directly or indirectly, by divergent natural selection. However, major work remains to be done to objectively determine the traits and genomic regions directly and causally subject to selection and which are most critical for driving speciation. I will discuss how progress on this front can be made using emerging ‘ecological’ model systems in which genome variation can be experimentally studied in the wild.

# Loss of function mutations in MC4R drive adaptation of Astyanax mexicanus through hyperphagia. (51852)

Nicolas Rohner, Ariel Aspiras, Richard Borowsky, Cliff Tabin.

Colonization to new environments necessitates changes to morphology, behavior, and physiology. Especially how the latter two evolve remains largely a mystery. The independently derived cavefish populations of Astyanax mexicanus are providing a unique opportunity to study metabolic adaptation to nutrient-poor environments. As the hallmark of cave environments is the scarcity of food, cavefish have adapted different strategies to survive, such as starvation resistance and binge eating when food becomes available. We show that while all cavefish populations tested lose weight slowly during starvation, only some consume more food than surface populations. Here we show a mutation in a conserved residue of melanocortin 4 receptor (MC4R), contributing to this insatiable appetite. Intriguingly, the same mutated residue has been shown to be linked to obesity in humans. We demonstrate that the mutation results in reduced signaling sensitivity in vitro. We further validate in vivo that the mutated allele contributes to elevated appetite and growth. The mutation is fixed in most cave populations and we provide evidence that this could be due to selection from standing genetic variation in surface populations. Our results suggest that drastic metabolic and behavioral changes can occur by coding changes in a single gene in natural populations.

# Identifying the molecular basis of adaptation and genomic divergence in Heliconius butterflies (51901)
**Nicola Nadeau**, Carolina Pardo-Diaz, Annabel Whibley, Megan Supple, Mathieu Joron, Owen McMillan, Chris Jiggins.

*The University of Sheffield; Universidad del Rosario; Muséum National d'Histoire Naturelle;*
*The Australian National University; Smithsonian Tropical Research Institute; University of*
*Cambridge.*

The Heliconius butterflies are known for their bright wing colour patterns, which are divergently selected between populations, but convergently selected within a location, leading to mimicry between species. We have described genome-wide patterns of divergence between adjacent populations that are divergently selected for colour pattern and meet in narrow hybrid zones. This has revealed that narrow genomic regions containing the colour pattern controlling loci are differentiated between populations. We have used this information, together with genetic data from other populations and species that share colour pattern alleles, to narrow down the genomic regions and identify the particular genes underlying pattern variation. One of these genes is an unexpected candidate, belonging to a family of conserved cell cycle regulators. We find strong associations between phenotypic variation and DNA sequence variation near this gene in three different Heliconius species, as well as associations between expression of this gene and colour pattern. This gene appears to have adopted a novel function in the Lepidoptera and become a major target for natural selection acting on colour and pattern variation in this group.

----- Caught in the crossfire: Genome defense in light of genomic autoimmunity (52618)

**Justin Blumenstiel**, Alex Erwin, Mauricio Galdos, Michelle Wickersheim, Chris Harrison, Kendra Marr.

*University of Kansas.*

For systems of immunity, a fundamental challenge is to achieve an appropriate balance between sensitivity and specificity in distinguishing self from non-self. Small RNA-based systems of genome defense identify transposable elements (TEs) via aberrant insertions or insertions into genomic regions dedicated to small RNA production. In turn, the production of anti-TE small RNAs from these insertions can mediate transcriptional and post-transcriptional TE silencing. A significant cost of genome defense is off-target gene silencing. Using a system of hybrid dysgenesis in Drosophila virilis as a model, we have demonstrated how effective genome defense is sensitive to the dose of multiple protective elements. These studies also show how TE destabilization can lead to increased off-target effects within and across generations. Using molecular evolutionary analysis in Drosophila, we find that the primary evolutionary response to increased TE burden is increased translational efficiency of the piRNA machinery. Altogether, these results support a model in which the evolution of genome defense is governed by a tension between sufficient TE repression and off-target effects. I propose that this tension - between sensitivity and specificity - is a key driver in the evolution of systems of genome defense mediated by small RNA pathways.
## The punishment wars (53352)

**Toby Kiers.**

*Department of Ecological Science, Vrije Universiteit Amsterdam.*

How is conflict suppressed? In most mutualisms, an individual host associates with multiple partners that can vary dramatically in the benefit they provide. This creates a potential tragedy of the commons where less-mutualistic partners potentially share in the collective benefits, while paying less of the costs. Our focus is on understanding specific mechanisms that reduce the fitness benefits from cheating, such as sanctions and reciprocal rewards. These mechanisms can play a key role in the evolution of egalitarian cooperation. Ultimately, our aim is to identify patterns of conflict suppression and conflict resolution across diverse mutualistic systems, such as rhizosphere mutualisms.

## The origins, persistence and decay of bacterial mutualisms (51759)

**Lee Henry, Godfray Charles.**

VU Amsterdam; University of Oxford.

Bacterial symbiosis has played a fundamental role in the evolution of eukaryotes. However, we still know little about how cooperative relationships with bacteria originate, and why they form in some host species but not others. Facultative symbionts that are beneficial, but not essential, provide unique insights into these processes. Here we use the facultative symbionts of over a hundred aphid species to test how host life history and relatedness of host species influences horizontal transmission, persistence and decay of bacterial mutualism.

## ‘Currency’ exchange underlying the long-term association between squid and bioluminescent bacteria (52192)

**Natacha Kremer, Julia Schwartzman, Edward Ruby, Margaret McFall-Ngai.**

University of Madison-Wisconsin, USA; Université Lyon 1, UMR CNRS 5558, France.

Long-term stability of horizontally transmitted symbioses must rely on negotiations between partners that result in a gain of fitness for the association. The study of invertebrate species that coevolved with simple microbial communities provides the opportunity to decipher the
chemical conversation between partners, and to highlight the ‘currency’ exchange that
contributes to the stability of ‘egalitarian’ cooperative associations. In particular, the
symbiosis between the Hawaiian bobtail squid and its luminescent bacterial partner, Vibrio
fischeri, is tractable in its natural environment. The squid light organ is colonized after
hatching by V. fischeri, which participates in the squid’s camouflaging behavior. We showed
that in the mature symbiosis, host hemocytes migrate toward and release chitin into the
symbiotic crypts of the light organ at dusk. This polymeric glycan is used as carbon source
and catabolized by symbionts during the night, acidifying the crypt environment. Because
oxygen is released from the circulating carrier protein, hemocyanin, in response to a decrease
in pH, this acidification increases the amount of oxygen available to the symbionts overnight.
Symbionts thus have an increased ability to produce light by their luciferase, whose activity
could also be a way to limit a potential toxic effect of free oxygen.

Spatial exclusion of non-cooperators from released public goods stabilizes inter-specific cooperation (52231)

Samay Pande, Filip Kaftan, Stefan Lang, Sebastian Germerodt, Ales Svatos, Christian Kost.

Experimental Ecology and Evolution group, Max Planck Institute for Chemical Ecology, Jena, Germany; Research Group Mass spectrometry, Max Planck Institute for Chemical Ecology, Jena, Germany; Department of Bioinformatics, Friedrich Schiller University Jena, Jena, Germany; Evolutionary biology group, ETH Zurich, Switzerland.

Metabolic cross-feeding interactions are ubiquitous in natural microbial communities. Explaining their maintenance, however, is challenging, because organisms should avoid investing costly resources into unrelated individuals. We hypothesized that positive assortment within structured environments such as microbial biofilms can maintain mutualistic cross-feeding. To test this, we engineered Escherichia coli and Acinetobacter baylyi to reciprocally exchange essential amino acids. Interspecific coculture experiments confirmed that non-cooperating types were selectively favoured in spatially unstructured (liquid culture), yet disfavoured in spatially structured environments (agar plates). An individual-based model and experiments with engineered genotypes indicated that a segregation of cross-feeders and non-cooperating auxotrophs stabilised cooperative cross-feeding in spatially structured environments. Finally, chemical imaging confirmed that auxotrophs were indeed spatially excluded from cooperative benefits. Together, these results demonstrate that in structured environments such as bacterial biofilms, cooperative cross-feeding between different bacterial species is favoured by excluding non-cooperators from cooperative benefits, which could help to explain the widespread distribution of these ecological interactions in nature.

The crucial link between ‘how’ and ‘why’ in the evolution of environmental sex determination (51813)
**Lisa Schwanz.**

UNSW Australia.

For many organisms, developing as a male or female depends primarily on environmental factors such as temperature or social conditions – a phenomenon known as Environmental Sex Determination (ESD). The costs of such a biological feature in a world with fluctuating or changing environments are high, and the benefits remain largely a matter of conjecture in the field of sex allocation. Instead, the benefits of Genotypic Sex Determination (GSD) seem obvious, and the challenges of transitioning away from GSD seem insurmountable. Despite this, sex-determining mechanisms are highly evolutionarily labile in some taxa, thus demanding evolutionary hypotheses. In this talk, I will discuss my theoretical and empirical research into the forces shaping the evolution of environmental sex determination (mostly temperature-dependent sex determination in reptiles). In particular, I will focus on how knowledge of the mechanisms of ESD can reveal 1) the simplicity of evolutionary transitions between sex-determining mechanisms, thus allowing ESD to evolve easily in response to selection; and 2) the plasticity in sex ratio afforded by linking developmental biology to environmental factors, thus facilitating selective advantages of ESD.

Session 1 WED GEN C 2

# Sex allocation in simultaneous hermaphrodites: lessons from an emerging model organism (52767)

**Lukas Schärer.**

University of Basel.

Anisogamous sexual reproduction involves two fundamentally different routes to fitness, namely the male and female sexual strategies, which at their root entail making many small or fewer large gametes, respectively. These two strategies are tightly linked by the rules of sex allocation, because every zygote has one father and one mother, and so exactly one half of the fitness in a population necessarily derives from either sex function. While the two strategies can be distributed over individuals in a population in many different ways, research on sex allocation in animals has primarily focused on species with separate sexes. Over the past decade my research group has established the free-living flatworm Macrostomum lignano as a powerful emerging model to study sex allocation and other aspects of anisogamous sexual reproduction in simultaneous hermaphrodites, including experiments involving phenotypic plasticity, phenotypic engineering, transgenesis, transcriptomics, and experimental evolution. Among other insights this research has clearly identified local sperm competition, i.e. the competition between related sperm for fertilizations, as a key factor for hermaphrodite sex allocation. Moreover, it is becoming clear that local sperm competition also helps to clarify general aspects of the evolution of sex roles in other species with anisogamous sexual reproduction.
# Sex allocation, juvenile mortality & the costs imposed by offspring on parents and siblings (51765)

Andrew Kahn, **Michael Jennions**, Hanna Kokko.

*The Australian National University; The Australian National University; University of Zurich.*

In general, sex-specific adult mortality is not expected to affect optimal patterns of sex allocation. Several authors have, however, made verbal arguments that this is not true for sex-specific juvenile mortality during the period of parental care. We teach this to undergraduates, but lack a model confirming the argument is sound. Here, we provide formal mathematical models exploring how such juvenile mortality affects optimal sex allocation. We confirm the prediction that biased production of the sex with higher mortality during care is favoured. Crucially, however, this is only true when this juvenile mortality frees up resources for current/future siblings (i.e. the saved investment is transferable). Furthermore, we show that while optimal sex allocation is consistent with the theory of equal investment (as asserted by previous authors, and reflecting how we teach sex allocation theory), thinking in terms of equal investment is not readily feasible in some scenarios. We also show that differences in early mortality overcome biased sex allocation such that the sex ratio at independence is generally, but not always, biased in the opposite direction from that at birth. Our models should be useful to empiricists investigating sex-specific juvenile mortality and, as importantly, to those teaching sex allocation theory to their students.

# The evolution of unisexual flowers within inflorescences (52179)

**Rubén Torices**, Ana Afonso, Marcos Méndez.

*Estación Experimental de Zonas Áridas (CSIC); Department of Ecology and Evolution, University of Lausanne; Centre of Functional Ecology. University of Coimbra; Biodiversity and Conservation Unit, Rey Juan Carlos University.*

The evolution of unisexual flowers within inflorescences has been explained as a mechanism of avoiding self-fertilization reducing the negative effects of inbreeding. However, many species with unisexual flowers also have self-incompatibility systems making difficult generalizations of this hypothesis. An alternative hypothesis for this pattern is that flowers within inflorescences compete by resources, and that the sequential development of flowers and architectural constraints lead to a gradient on resource availability. This variation on resource availability produces distinct optima for sex allocation accordingly with the position of the flower within an inflorescence, potentially driving the evolution of sexual specialization on separated flowers. Using as a model the largest family of flowering plants (Asteraceae), we explored this hypothesis. We measured number of flowers and capitulum size to estimate flower density (as a proxy of floral competition) in 101 species with different levels of sexual specialization: hermaphroditic (only bisexual flowers), gynomonoecious (bisexual and female flowers) and monoecious species (female and male flowers). We found that flower number and flower density were higher on those species with a higher degree in sexual specialization,
supporting that an increasing on floral competition might favor sex specialization of male and female functions on different flowers.

# Genomic conflict over sex allocation in the parasitoid wasp Nasonia vitripennis. (51786)

**Nicola Cook**, Michael G Ritchie, Bart A Pannebakker, Eran Tauber, David M Shuker.

*University of St Andrews; University of Wageningen; University of Leicester.*

The study of sex ratios has produced an extraordinarily rich theoretical literature and provides an ideal basis to examine genetic constraints on adaptation. Here, we consider adaptive sex allocation behaviour in the parasitoid wasp Nasonia vitripennis, a species which allocates sex in line with Local Mate Competition (LMC) theory. Despite extensive behavioural work on sex allocation in Nasonia, we know rather little about the genetic basis of sex allocation in this species. However, recent theory has highlighted how genomic conflict may influence sex allocation under LMC, conflict that requires parent-of-origin information to be retained by alleles via an epigenetic signal. We manipulated whole-genome DNA methylation in N. vitripennis females and examined how they allocated sex. Disruption of DNA methylation did not ablate the facultative sex allocation response as sex ratios still varied in line with classical LMC theory. However, our data were consistent with predictions from genomic conflict over sex allocation theory and suggest that observed sex ratios are closer to the optimum expected for maternally- rather than paternally-inherited alleles. Our results also emphasise how elucidating the mechanism of well-understood behaviours can further enrich our understanding of them.

# Sperm storage and the size advantage model of sex allocation in the protandrous sex-changer Crepidula fornicata (52232)

**Thomas Broquet**, Audrey Barranger, Emmanuelle Billard, Anastasia Bestin, Rémy Berger, Gaëlle Honnaert, Frédérique Viard.

*CNRS - Station Biologique de Roscoff.*

Sex allocation theory shows that sequential hermaphroditism is adaptive when one sex has a steeper size-fitness curve than the other. Typically, protandry (male-first sex change) is selected for when female fecundity depends on body space for the production of eggs while male reproductive value is less dependent upon size. However, size might also be decisive for males, depending upon the mating system. Which sex has the steepest increase in reproductive value with size determines the direction of sex-change. The slipper limpet Crepidula fornicata is a protandrous gastropod, and yet male success is thought to increase strongly with size in this species. Theory therefore predicts that large females have yet a
higher reproductive rate. We tested this prediction using size-fitness curves for each sex obtained from experimental breeding and paternity assignment. In agreement with the size-advantage theory male reproductive success increased with size due to the polygamous system but females nonetheless had a higher success than equally-sized males. Interestingly, this was partly due to sperm storage effects, which appeared a critical determinant of success of both sexes. Moreover, modeling the effect of sperm storage shows that it could hasten sex-change in protandrous species, depending on sperm replacement mechanisms.

**The evolution of transgenerational integration of information in
heterogeneous environments (52246)**

**Olof Leimar, John McNamara.**

*Stockholm University; University of Bristol.*

An organism's phenotype can be influenced by maternal cues and by directly perceived environmental cues, as well as by its genotype at polymorphic loci. In fluctuating environments, natural selection favors organisms that efficiently integrate different sources of information about the likely success of phenotypic alternatives. In such situations, it can be beneficial to pass on maternal cues for offspring to respond to. A maternal cue could be based on environmental cues directly perceived by the mother, but partly also on the cues that were passed on by the grandmother. We have used a mathematical model to investigate how the passing of maternal cues and the integration of different sources of information evolves as a response to qualitatively different kinds of temporal and spatial environmental fluctuations. The model shows that passing of maternal cues and transgenerational integration of sources of information readily evolves. Factors like the degree of temporal autocorrelation, the predictive accuracy of different environmental cues, and the level of gene flow strongly influence the expression of adaptive maternal cues and the relative weights given to different sources of information. We outline the main features of the relation between the characteristics of environmental fluctuations and adaptive systems of phenotype determination and compare these predictions with empirical studies.

**Maternal effect on worker size in the seed harvester ant *Pogonomyrmex rugosus* (52338)**

**Silvia Paolucci, Benjamin Czech, Gregory Hannon, Tanja Schwander, Laurent Keller.**

*Department of Ecoloy and Evolution, University of Lausanne, Switzerland; Cold Spring Harbor Laboratory, New York, USA.*

Eusocial insects are characterized by extreme phenotypic plasticity, in which different phenotypes can be produced within the same colony depending on environmental conditions.
For example, worker sizes change dramatically across different stages of the colony life cycle. Young founding colonies produce many small workers, instead of few large ones, which are only found in established colonies. The degree to which worker size is regulated through differential feeding during development or controlled by the mother queen via maternal effects remains unknown. We tested for maternal effects influencing the size of workers in the ant <i>Pogonomyrmex rugosus</i>. A cross-fostering experiment showed that eggs laid by young founding queens developed into smaller workers compared to the ones produced from eggs laid by old queens from established colonies, when both egg types were raised by workers from established colonies. Moreover, eggs laid by old queens failed to develop when cross-fostered to founding queens. These results indicate that maternal effects influence worker size and egg survival. To further investigate how these effects can influence the developmental fate of the brood I am quantifying gene expression differences between eggs from old and young queens with a particular focus on the possible role of microRNAs.

## Pollution-induced non-genetic inheritance and its effect on eco-evolutionary dynamics (52395)

Stewart Plaistow, Brian Chan, Helene Collin, Steve Paterson.

University of Liverpool.

Theory suggests that genetic and non-genetic inheritance (NGI) mechanisms shape the process of phenotypic evolution, yet empirical studies demonstrating the ecological and evolutionary significance of NGI are lacking. We addressed this by testing the hypothesis that pollution induced NGI can alter the ecological and evolutionary dynamics of populations. 10 Daphnia pulex clones from the same source population were kept as monoclonal populations in polluted and control environments for a year. Animals from these populations were then used to set up competition trials comprising of 40 genetically identical populations (equal proportions of the 10 clones) exposed to four different combinations of ancestral and current pollution exposure (P/P, P/NP, NP/P, NP/NP). Over the following ten months persistent differences in the population dynamics of the four treatment groups were detected, including a significant effect of NGI. We used image analysis and microsatellite analysis to determine whether differences in the dynamics of the four different types of population were explained by differences in the age-structure of populations, differences in the individual 'state' dynamics of populations, or differences in the evolutionary dynamics of populations (measured as changes in the relative frequency of different clones over time).

## Genetic basis of variation in thermal plasticity for body pigmentation (52662)

Elvira Lafuente, Patrícia Beldade.

Instituto Gulbenkian de Ciencia.
External environmental cues can influence developmental rates and trajectories leading to the production of different phenotypes from the same genotype. This developmental plasticity sometimes results in a better match between adult phenotype and the environment the organism will experience, and thus helps organisms to cope with environmental heterogeneity. Plasticity is a complex trait that is heritable, subject to selection, and, therefore, can evolve. We know of single alleles that confer environmental sensitivity and of the polygenic nature of changes in reaction norms. However, little is known about the specific loci contributing to natural variation in plasticity. We focus on thermal plasticity in body pigmentation in Drosophila melanogaster to explore the genetic basis of inter-genotype variation in reaction norms. We reared flies of over 200 different genotypes at different temperatures, quantified adult color and color pattern, and unraveled genetic differences in the height, slope, and/or shape of reaction norms. These data are now being used to identify the sequence variants responsible for such differences and uncover specific loci, gene classes (e.g. enzymes vs transcription factors), and gene regions (e.g. coding vs. regulatory) that can provide raw material for evolutionary change in plasticity.

# Transgenerational effects of diet through the maternal and paternal lineage (52765)

Z. Valentina Zizzari, Nico M. van Straalen, Jacintha Ellers.

VU University Amsterdam.

Food shortage is an important selective factor that can influence population abundance. Yet, despite its role in shaping life-history trajectories, many aspects of the interaction between parental and offspring food environments remain unclear. In this study we used a cross-generational split-brood design where diet quantity was manipulated over two generations. Our model system is Orchesella cincta, a springtail found in the litter layer of forests and feeding primarily on algae. We tested for the within-generation effects of diet and the relative contribution of each parental sex on the performance of offspring reared under matched and mismatched environments. We found adverse effects of food limitation on growth rate and reproductive performance of the parental generation. Offspring life-history strategies were primed by the diet of both parents. Offspring born to food-restricted parents reached maturity faster than offspring born to well-fed parents, irrespective of their own diet. However, mismatches between adult and offspring environments also generate sex-specific adverse effects: parents on high-diet produced daughters which had a lower growth rate under a low-diet. In conclusion, we showed that in Orchesella cincta offspring life-history strategies may be set by the nutritional history of both parents with different outcomes in female and male offspring.

# Age-dependent plasticity in reproductive effort is driven by metabolic reserves and mating opportunities, not adaptive allocation strategies (52446)
**Thomas Houslay**, Kirsty Houslay, James Rapkin, John Hunt, Luc Bussière.

*University of Stirling; University of Dundee; University of Exeter.*

When males express an energetically expensive sexual signal repeatedly over their lifetime, trade-offs between current and future signal investment often cause plasticity in patterns of age-dependent signal expression. This variation in reproductive effort with age might represent alternate adaptive strategies (live fast, die young vs. slow and steady), or it could arise simply through condition-dependent constraints on allocation ('late bloomers' do not have early investment options). Testing these alternatives is difficult: resource acquisition and allocation are elusive quantities, and metabolic reserves both cause and are affected by reproductive effort.

To disentangle the causal relationships between resource acquisition and age-dependent reproductive effort, we manipulated acquisition (through diet) and sexual trait allocation (via access to potential mates) in male decorated crickets, Gryllodes sigillatus, while simultaneously assessing age- and signalling effort-mediated changes in metabolic storage components. Increased access to dietary resources caused increased calling effort and metabolic storage, while access to females increased both the likelihood of calling and time spent calling. Males with lower resource budgets called less than rivals, but still suffered metabolite storage loss and viability costs; our results suggest reduced signalling in lower-acquisition treatments was due to energetic constraints rather than an adaptive resource-accumulation strategy.

## Can't do it alone: Buchnera and its very different partners (52473)

**Amparo Latorre.**

*Institut Cavanilles de Biodiversitat i Biologia Evolutiva, Universitat de València, València, Spain.*

Most aphids harbour the obligate endosymbiotic bacterium Buchnera aphidicola that endow them with several metabolic capabilities required for their survival. Through whole genome sequencing we have determined that in the subfamily Lahninae, Cinara tujafilina, Cinara cedri (both Eulachnini) and Tuberrolachnus salignus (Lachnini) have established co-obligate associations with the typical B. aphidicola and the secondary symbiont Serratia symbiotica. Nevertheless, while in C. tujafilina this endosymbiont is extracellular, rod shape and possesses a big genome, in C. cedri and T. salignus it is intracellular, pleomorphic and has very small genomes that have apparently emerged independently. We have previously proposed that the loss of the riboflavin biosynthesis pathway in the Buchnera from the Lachninae common ancestor, caused S. symbiotica to fix as an obligate endosymbiont. Nevertheless, some other Lachninae aphids have been found to be associated to other bacterial taxa, rather than S. symbiotica. We have analysed many representatives from the Lachninae and have corroborated that all possess a co-obligate endosymbiont, and while for most it is S. symbiotica, some members have lost this ancient endosymbiont that has been replaced by different bacterium.
# How are negative fitness consequences of evolutionary trait loss compensated?
(53321)

Nathan Bailey, Sonia Pascoal.

University of St Andrews.

Trait loss or reduction may evolve under favourable selective conditions, for example due to
new interactions with other species or changed environmental conditions. However, the
evolutionary loss of a trait is likely to cause negative pleiotropic fitness effects involving
other traits. The likelihood that a mutation obliterating or reducing a trait will persist depends
on how such negative effects are mitigated, either through rapid evolutionary change,
phenotypic plasticity, or other mechanisms. My work tackles this problem using a field
cricket that has recently lost the ability to produce calling song. The evolutionary loss of song
was driven by an acoustically orienting predator, is caused by a morphological change, obeys
simple patterns of Mendelian inheritance, and has demonstrable negative pleiotropic effects. I
will illustrate the genomic architecture of song loss in two populations and provide evidence
that despite its convergent effects, it evolved independently in each. Data from genetic
mapping, gene expression profiling and proteome screens illuminate the mechanistic basis of
the loss, and I test specific predictions about gene expression changes that might mitigate the
mutation's detrimental effects. Understanding not only the selective forces that lead to trait
loss, but also the genomic context that facilitates or constrains such evolutionary change,
enhances our understanding of the evolvability of different types of adaptations in nature.

Genomic signatures of sexual trait decay in an asexual wasp (51940)

Ken Kraaijeveld, Yahya Anvar, Jeroen Frank, Johan den Dunnen, Jacintha Ellers.

VU University Amsterdam; Leiden University Medical Center.

When animal lineages switch from sexual to asexual reproduction, redundant female sexual
traits consistently decay at a rapid rate. Male sexual traits, which are also redundant but not
exposed to selection in asexuals, decay at a much slower rate. The genetic mechanisms
underlying sexual trait decay are unknown. Genes for redundant traits may accumulate
random mutations and become pseudogenes. Alternatively, the expression of sexual genes
may be suppressed in asexuals. We sequenced the genomes of a sexual and an asexual lineage
of the parasitoid wasp Leptopilina clavipes and found evidence of random mutation
accumulation. After annotating the genome, we catalogued mutations that changed the amino
acid sequence of the protein. Gene ontology analysis of affected genes identified several that
are involved in olfactory receptors and other traits known to have decayed in the asexual
lineage. While we cannot exclude that trait decay results from suppression of redundant
genes, our results suggest that at least some sexual genes have acquired loss-of-function mutations in the asexual lineage.

# Explaining siderophore loss, cross-use and exploitation in natural Pseudomonas communities (51954)

**Elena Butaite**, Rolf Kuemmerli.

*University of Zurich.*

Fluorescent pseudomonads typically secrete the siderophore pyoverdine (PVD) to scavenge iron from the environment. PVD production is often partially or fully lost in the laboratory because PVD is either not needed under certain culturing conditions, or favours non-producing mutants that act as cheats exploiting the PVD as a public good.

Here, we investigate the pattern of trait loss and PVD exploitation among 920 natural Pseudomonas strains, isolated from soil and pond habitats. We found that PVD trait loss (partial or full) was significantly more common in habitats with higher iron content and lower pH, where iron is more bioavailable. These patterns suggest that trait loss is driven by disuse. However, we also found that PVD producers and non-producers often co-existed in the same community. A mixture of cross-feeding and competition assays revealed that many non-producers could capitalize on the PVD produced by other community members. We also found evidence for local antagonistic interactions because non-producers were better at using the PVD from non-community than community members. Altogether, our data suggest that PVD loss in natural communities is driven by both social and ecological factors, and that PVD exploitation can select for novel, more exclusive variants of PVD.

# Strong selection for a loss of metabolic autonomy in bacteria (51955)

**Glen D'Souza**, Silvio Waschina, Christian Kost.

*Experimental Ecology and Evolution Research Group, Max Planck Institute for Chemical Ecology; Theoretical Systems Biology Group, Friedrich-Schiller-Universität Jena.*

Bacteria that adapt to specialised environments frequently lose biosynthetic genes, which render them dependent on an environmental uptake of the corresponding metabolites.

However, it remains generally unclear whether selection or drift is driving this genome-streamlining. Here we experimentally determined the propensity of bacteria to lose biosynthetic functions when the metabolite is environmentally available. For this, we serially propagated replicate lines of the bacterium Escherichia coli for 2,000 generations in an amino acid-containing environment. A subsequent quantification of auxotrophic mutants revealed that genotypes that essentially required amino acids to grow evolved already after 250 generations and were highly abundant (up to 60%) in all replicate populations after 2,000
generations. Derived auxotrophic mutants were significantly more productive and fitter than the prototrophic ancestor in the presence of amino acids. However, this growth advantage was lost in amino acid-deficient environments, suggesting environmental compensation of amino acids contributed to the observed gains in fitness. Our study provides quantitative evidence that nutrient-containing environments exert a strong selection pressure for a loss of metabolic functions in bacteria and has significant implications for the evolution of microbial genomes.

# Loss and (re)gain of color vision in deep-sea fishes: uncovering the secrets of 100 teleost genomes. (52766)

**Zuzana Musilova**, Fabio Cortesi, Martin Malmstrøm, Ole Tørresen, Sissel Jentoft, Walter Salzburger.

*University of Basel, Switzerland; University of Queensland, Australia; University of Oslo, Norway.*

Color vision in vertebrates is made possible by the expression of different visual genes (cone opsins for photopic 'color vision' and rod rhodopsin for scotopic 'dim-light' vision) in retina. In teleost fishes, opsin genes have continued to duplicate creating an astonishing array of photoreceptors, considered to be crucial to adapt to the varying light conditions. Deep-sea fishes have evolved several physiological adaptations including larger eyes or rod-only retinas to counteract the low light conditions of their environment. However, the molecular mechanisms of dim-light-only vision and the loss of color vision remains poorly understood. Here we report opsin gene evolution based on 100 genomes spanning the teleost phylogeny, with emphasis on the deep-sea fish lineages. We found strong evidence for cone opsin losses and pseudogenization in many of the deep-sea fishes, confirming the absence of color vision in these lineages. Moreover fish lineages that have re-emerged from the deep-sea to colonize shallow waters, revealed a rapid expansion and functional diversification of the remaining formerly 'green tuned' cone opsin. Most importantly, we found that one deep-sea fish lineage had evolved multiple rhodopsins adapted to different dim-light wavelengths, assuming what may be the first evidence for rhodopsin-based color vision in vertebrates.

# Identifying locally adaptive loci by scanning for barriers to introgression (52506)

**Andrea Fulgione**, Joachim Hermisson, Angela Hancock.

*University of Vienna.*

Maintenance of locally adapted alleles in the face of gene flow is a pervasive evolutionary process, but characterizing the historical and biological details of admixture and introgression events in actual populations is a major challenge. However, continent-island systems provide
simplified cases where it is possible to reconstruct specific evolutionary events that lead to
contemporary patterns of genetic variation.

The Canary Islands harbor exceptional species diversity and divergence, likely a result of ancient pre-glacial colonization events. Modern populations of Arabidopsis thaliana in the Canary Islands result from admixture of an anciently diverged native population and a recently introduced mainland population. To characterize demographic and adaptive histories in the Canary Islands, we collected whole-genome sequence data from natural populations of Arabidopsis throughout Macaronesia and leveraged data from worldwide samples. We developed a haplotype-based genome scan to perform admixture deconvolution and we identified genomic loci that represent strong barriers to gene flow as well as loci that underlie adaptive introgression from the invaders.

A worldwide perspective on isolation-by-distance patterns in humans (52619)

Benjamin Peter, Desislava Petkova, Matthew Stephens, John Novembre.

*Department of Human Genetics, University of Chicago, USA; Department of Statistics, University of Chicago, USA; Department of Statistics, University of Oxford, UK.*

Human genetic diversity has been shaped by the initial expansion of humans across the globe and subsequent migration and admixture events. Throughout this history, geographical features such as mountains, oceans, and deserts have presumably shaped rates of gene flow between populations. To obtain maps that represent the spatial structure of human genetic diversity, we jointly estimate migration rates and local diversity using a recently developed, spatially explicit method (EEMS, Estimation of Effective Migration Surfaces). We apply EEMS on global, continental, and sub-continental scales, analyzing genetic data from more than five thousand individuals from multiple studies across the globe. We find many geographical features are indeed barriers with regards to effective migration. In particular, the Saharan Desert, the Mediterranean Sea, and the straits between South-East Asia and Melanesia emerge as particularly strong barriers to migration. High migration rates are found in a corridor connecting Europe with China. In contrast, we find that diversity parameters vary more smoothly, decreasing gradually with distance from Africa. Overall, our results suggest that diversity patterns are consistent with the signature of the Out-of-Africa expansion, but that migration rates are more strongly influenced by geography.

Genetic variation linked to climate adaptation in Arabidopsis lyrata (52656)

Marco Fracassetti, Yvonne Willi.

University of Neuchâtel.
Global climate change has heightened the interest to understand climate adaptation and limits to such adaptive evolution. Progress in the field depends on knowing the genes under this selection and the distribution of genetic variation. We performed a genome-wide association study (GWAS), linking genetic variation with climate variables. The study organism was the North American Arabidopsis lyrata spp. lyrata, a short-lived herb occurring on sand dunes and rocky outcrops with well-separated and stable populations. We re-sequenced pools of DNA of 55 populations covering the whole geographic range of the subspecies and revealed population-level single-nucleotide-polymorphism (SNP) frequency data. Climate data based on temperature and precipitation and soil data were used for the GWAS.

We used a dual approach to detecting SNPs linked to climate variables. First, we analyzed site frequency spectra to detect signatures of selection within populations. Second, we tested SNPs for correlation with climate variables by accounting for genetic structure among populations. SNPs that were significant in both types of analyses were taken as candidates for being relevant in climate adaptation. We discuss the approach taken and the list of genes that is likely relevant for adaptation in the context of climate change.

# The role of host plant adaptation in genomic divergence and diversification of Timema stick insects (52805)

**Moritz Muschick**, Victor Soria-Carrasco, Stuart R. Dennis, Zachariah Gompert, Aaron A. Comeault, Jeffrey L. Feder, Patrik Nosil.

*Department of Animal and Plant Sciences, University of Sheffield, UK; Department of Biology, Utah State University, USA; Department of Biological Sciences, University of Notre Dame, USA.*

How the often-continuous processes of speciation and adaptive radiation unfold from beginning to end is poorly understood, but is of central importance for understanding biological diversification. One hypothesis is that shifts between very different peaks in the adaptive landscape, although difficult to achieve, are required to generate strong reproductive isolation. Here we test this hypothesis using a combination of ecological data, experimental estimates of reproductive isolation, and both reduced representation and whole genome sequence data from multiple species of herbivorous Timema stick insects. We find that extreme ecological shifts between conifer and flowering plant hosts are more rare than moderate host shifts between flowering plant families, but that such extreme host shifts generate stronger reproductive isolation. Despite clear effects of the magnitude of host shift on reproductive isolation, overall genomic divergence is more strongly promoted by geographic separation. In comparison, host adaptation causes heterogeneous, genomically localised genetic divergence. The results highlight the different but complementary roles of ecology and geography in driving transitions across the speciation continuum.
# The flexible genome: uncovering the regulatory basis of phenotypic plasticity.
(52862)

**Vicencio Oostra**, Marjo Saastamoinen, Bas J. Zwaan, Christopher W. Wheat.

*University College London (UK); University of Helsinki (Finland); Wageningen University (The Netherlands); Stockholm University (Sweden).*

Phenotypic plasticity is the ability of a given genotype to express different phenotypes in response to environmental variation, often as adaptation to fluctuations in habitat quality. Studying the regulatory basis of plasticity provides insights into the mechanistic basis of this important adaptation, and into how genes and the environment interact to produce complex phenotypes. To study the genetic basis of plasticity we use the afrotropical butterfly Bicyclus anynana, which displays life history plasticity as adaptation to its habitat's wet-dry seasonality. We combine a full-sib quantitative genetics design with RNAseq, yielding transcriptome-wide estimates of gene expression variation as a function of genetic background, environment, and their interaction. We constructed a de novo assembly, yielding 7365 genes after filtering, and identified season-specific genes, as well as genes whose environmental response in expression was affected by genetic background, indicating genetic variation for plasticity at the transcriptome level. We then asked whether plasticity-related genes were depleted vs. enriched in nucleotide diversity compared to non-plastic genes, indicating constraints vs. potential for evolutionary responses. Our study provides new insights into the regulatory links between juvenile conditions and adult life history.

# Ecological genetics of local adaptation in Arabidopsis thaliana (52733)

**Jon Ågren**, Christopher G. Oakley, Sverre Lundemo, Douglas W. Schemske.

*Dept of Plant Ecology and Evolution, EBC, Uppsala University, Norbyvägen 18 D, Uppsala, Sweden; Dept of Plant Biology, Michigan State University, East Lansing, MI 48824, USA.*

Organisms inhabiting different environments are often locally adapted, yet in most cases the genetic and functional mechanisms of local adaptation are poorly understood. We mapped Quantitative Trait Loci (QTL) for total fitness and putatively adaptive traits, and determined the relationships between trait expression and fitness using a large RIL population derived from a cross between two locally adapted Arabidopsis thaliana populations, one in Italy and one in Sweden, and planted in field experiments at the parental sites for multiple years. We show that local adaptation is controlled by relatively few genomic regions of small to modest effect. A third of the 19 fitness QTL we detected showed evidence of trade-offs (locally favoured genotype reduces fitness elsewhere). Selection gradient analyses and mapping results indicated that QTL for flowering time and tolerance to cold contribute to fitness trade-offs. Sequence variation and functional analyses indicate that mutations in previously identified candidate genes may explain some of these trade-offs. Taken together, our results suggest that adaptation to markedly different environments can be achieved through changes in relatively few genomic regions, and that genetically based differences in both life history
and physiology contribute to adaptive differentiation and fitness tradeoffs among native A. thaliana populations.

# Individual variation in host health and its consequences for pathogen spread (52471)

**Pedro Vale.**

*University of Edinburgh.*

A major hurdle to reducing the burden of infectious disease is that individuals vary substantially in how sick they get and how sick they make others. Here I explore several sources of individual host variation and discuss its potential consequences for pathogen spread and evolution. Hosts may vary in how sick they get because of the variable use of damage limitation therapies. While these anti-virulence or tolerance-boosting drugs are promising “evolution-proof” alternatives to antimicrobials, I present some theoretical results highlighting that their use may, in some situations, lead to high prevalence of virulent pathogens. Hosts also vary in how sick they may make others, for example, when host heterogeneity in pathogen shedding is high, or when host behaviours increase the risk of infection spreading. I will discuss some experimental results of both viral and bacterial gut infections in Drosophila melanogaster. I explore how host genetics, sex and co-infection status may explain some of the heterogeneity in pathogen shedding, and test how key host behaviours are modified by infection. Behavioural responses during infection not only shed light on the risk of disease spread, they also reflect host health, revealing the more nuanced fitness costs of infection.

# Local adaptation to parasites suggests costs of migration and explains immunogenetic polymorphism in sticklebacks (52474)

**Joshka Kaufmann**, Tobias L. Lenz, Martin Kalbe, Manfred Milinski, Christophe Eizaguirre.

*Max Planck Institute for Evolutionary Biology, Department of Evolutionary Ecology; GEOMAR Helmholtz Centre for Ocean Research; School of Biological and Chemical Sciences, Queen Mary University of London.*

Local adaptation is often key to the process of speciation. Theory suggests that reduced fitness of migrants due to local maladaptation to foreign parasites could be sufficient to reduce gene flow between habitats and ultimately lead to speciation. Here, we experimentally investigated the relative fitness of migrants in foreign habitats, focusing on diverging lake and river ecotypes of three-spined sticklebacks. A reciprocal transplant experiment performed in the field revealed asymmetric costs of migration: while mortality of river migrants was increased under lake conditions, lake migrants suffered from reduced growth relative to river residents.
Focusing particularly on the parasitic environments, we found that macroparasite
communities did not only differ between lake and river residents but also between the
reciprocal migrants. This pattern of differential parasitisation had consequences for both the
innate and the adaptive immune system, where multiple habitat-specific associations between
parasite species and locally selected alleles of major histocompatibility immunogenes could
be detected. Altogether, these experimental results highlight the role of selection against
migrants in the early stages of ecological speciation and reveal complex resistance patterns
leading to immunogenetic diversity at the meta-population level.

Increased diversity at a locus involved in resistance to parasitism in Daphnia magna (52543)

Yann Bourgeois, Peter Fields, Gilberto Bento, Anne Roulin, Seanna McTaggart, Tom Little, Darren Obbard, Dieter Ebert.

Zoologisches Institut, Basel University; University of Edinburgh.

The study of processes that maintain adaptive genetic diversity have long interested
evolutionary biologists. From this perspective, host-parasite coevolution provides valuable
insights. In Daphnia magna, an emergent model species in epidemiology and evolutionary
biology, it has been suggested that interaction with the obligate bacterial endoparasite
Pasteuria ramosa fulfilled all the requirements for negative frequency-dependent selection to
occur. Recently, a 150 kb candidate genomic region involved in resistance to P. ramosa has
been identified in D. magna. This opens a new window to explore the effects of host-parasite
interaction on natural adaptive variation in this system.

Here, we took advantage of the recent sequencing of dozens of D. magna genomes sampled
across Eurasia. The candidate locus for resistance to P.ramosa displayed evidence for
selection. We found increased nucleotide diversity in the 200 kb flanking this locus and an
excess of alleles at higher frequencies compared to genomic background. At the resistance
locus itself, we observed indel polymorphism, suggesting that resistance could be tuned by
changes in copy number variation of resistance genes. We discuss the consistency of these
patterns with selective processes leading to the accumulation of polymorphism, such as
heterozygous advantage, negative frequency-dependent selection (Red Queen dynamics) and
local adaptation.

Variation in phenotypic selection on quantitative immune defence traits in a
freshwater snail (52671)

Laura Langeloh, Jukka Jokela, Otto Seppälä.

Eawag; ETHZ.
Understanding how phenotypic selection acts on immune function is important for predicting the outcomes of host-parasite interactions. While ecological factors affecting the range of phenotypic variation in immune traits and infection risk may strongly influence the form and strength of selection on immune defence, they have mostly been neglected in previous research.

In this study, Great Pond snails (Lymnaea stagnalis) from 6 populations were maintained individually in two different environments for 9 weeks: water enriched with opportunistic microorganisms to impose an immune challenge, or clean water. Survival, shell length, reproductive output and the level of two immune parameters, phenoloxidase-like activity and antibacterial activity, were recorded from each snail every second week.

Immune activity and reproductive output of snails differed between water quality treatments and populations. Selection gradient analyses suggested differences in selection on the examined immune traits. While no difference between the two laboratory environments could be detected, selection gradients differed across populations. Strong family-level variation in both immune traits within populations suggests sufficient genetic variation for response to selection.

# Diversity and divergence of immune genes in four wild rodent species (52718)

Andrew Turner, Mike Begon, Amy Pedersen, Steve Paterson.

University of Liverpool; University of Edinburgh.

Individuals vary substantially in their resistance to infectious disease and experiments on laboratory rodents, such as the house mouse (Mus musculus), have proved invaluable in elucidating the mechanistic basis of this resistance. However, controlled laboratory studies provide few insights into the causes and consequences of genetic variation in the natural environment, where increased genetic diversity, multiple infections and fluctuating environmental conditions are the norm. The study of wild rodents represents an excellent opportunity to link the functional genetic knowledge gained from laboratory rodents with the variation in disease susceptibility observed in natural populations, including humans.

Here we examined diversity in >800 immune genes and ~500 size-matched, non-immune genes in four wild rodent species: house mice, wood mice (Apodemus sylvaticus), field voles (Microtus agrestis) and bank voles (Myodes glareolus). In all species, genetic diversity was significantly higher in immune genes. Through examination and comparison of diversity within and between individuals, populations and species, we investigate which genes have been subject to natural selection, and whether the same genes have been repeatedly targeted by selection across different populations and species. For example, positive selection appears to have driven divergence between species at multiple pathogen-recognition sites within Toll-like receptor (TLR) genes.
# Constitutive protection, mismatch, and secondary exposure in transgenerational immune memory in the bumblebee Bombus terrestris (52848)

Seth Barribeau, Paul Schmid-Hempel, Ben Sadd.

East Carolina University; ETH Zürich; Illinois State University.

A number of invertebrates show evidence of immune memory or priming. Individuals given cues of a parasite either as a clearable dose or an inactivated inoculum are better able to resist a subsequent exposure than naive individuals or those given a different priming immune exposure. This immune history can also be transferred across generations with offspring having increased resistance to parasites that their parents were exposed to. Since invertebrates lack the antibodies and T-cells of the adaptive immune system, the mechanisms behind such memory remain mysterious. Here we describe the full transcriptome expression profile of transgenerational immune memory in the European bumblebee Bombus terrestris. We found that daughters of mothers exposed to an inactivated inoculum of the Gram-positive bacterium Arthrobacter globiformis constitutively express all known antimicrobial peptides at much higher quantities than daughters that have no immune history. We also describe how a mismatch between immune history and exposure results in a fundamentally different expression pattern. Finally, we explore whether receiving a second exposure to a bacterial inoculum results in greater immune activation.

# Intracellular endosymbiont selection contributes to Drosophila adaptation to viral infection (52942)

Vitor G. Faria, Nelson E. Martins, Sara Magalhães, Viola Nolte, Christian Schlötterer, Luis Teixeira, Élio Sucena.

Instituto Gulbenkian de Ciência, Oeiras, Portugal; Centre for Ecology, Evolution and Environmental Changes, Faculdade de Ciências, Universidade Lisboa; Institut für Populationsgenetik, Vetmeduni Vienna, Austria; Departamento de Biologia Animal, Faculdade de Ciências da Universidade de Lisboa, Lisboa, Portugal.

Bacteria of the genus Wolbachia are intracellular symbionts of many animal species. In Drosophila, Wolbachia has been shown to confer protection to RNA virus infection in a strain-dependent manner. Through experimental evolution, we have selected an outbred Wolbachia-infected population of D. melanogaster for increased resistance to DCV, a natural viral pathogen. Whole-genome sequencing of this population, upon 20 generations of selection, revealed that a Wolbachia sub-strain was fixed. Moreover, we show that challenged inter-population hybrids carrying either Wolbachia variant differ in their fitness, confirming the adaptive value to the host of selected endosymbiont. Finally, we re-assess host genome evolution upon Wolbachia clearance and DCV infection over 20 more generations. These findings demonstrate that the presence of protective endosymbiont plays a role in shaping the host genome and its own evolution may have a profound effect on host adaptation.
## Sexual conflict and social behaviour (52776)

**Tracey Chapman.**

*University of East Anglia.*

The intensity of sexual conflict over the level of expression of any reproductive trait value or behavior can be assessed by measuring its costs and benefits, in terms of lifetime fitness, for individuals of each sex. Though relatively underexplored, outcomes of sexual interactions between males and females can be viewed in terms of the wider context of social behaviors: i.e. Hamilton's famous quartet of social behaviors: mutual benefit (co-operation), selfishness, altruism and spite. Here I discuss how we can reclassify the outcome of interactions between males and females in this way. This reveals the potential for evolutionary disagreements between the sexes, and therefore sexual conflict, in all four types of social behavior classification – particularly so for selfish behavior. Central to this understanding is to clarify the meaning of costs and benefits in terms of positive or negative fitness consequences for males and females. Such fitness effects can be direct or indirect and although we expect sexual conflict to be low when relatedness is positive, it can still occur. I will discuss sexual conflict within this framework and provide examples.

## Inclusive fitness and sexual conflict (53362)

**Andy Gardner.**

*University of St Andrews.*

I will provide an overview of the theory of inclusive fitness and explore its application to the study of sexual conflict.

## The influence of relatedness on male entomopathogenic nematode aggression (51661)

Apostolos Kapranas, Maher Abigail, **Griffin Christine**.

*National University of Ireland, Maynooth.*

Males of entomopathogenic nematodes Steinernema spp. engage in aggressive contests that are fatal to losers. Previous studies suggest that males deriving from infective juveniles (IJ),
the free foraging stage that enters the insect host, are more aggressive. Theory predicts that, in closed systems with limited dispersal, intense competition should override any benefits of kin or at least higher aggression should be expected in mixed groups of relatives and non-relatives than in groups consisting solely of relatives or of unrelated animals (a dome-shaped effect). In this study, we examined how both relatedness and group size affect mortality rates among these post-IJ males in both semi-natural and natural conditions. We found that mortality rates are affected both by relatedness and group size. We discuss our findings in the context of current theory and also taking into account certain key life history characteristics of Steinernematid nematodes such as inter-specific competition and group dispersal. Entomopathogenic nematodes can provide new opportunities for testing the conflicting influence of competition and relatedness.

**Local mate competition mediates sexual conflict over sex ratio in a haplodiploid mite (51846)**

**Sara Magalhaes**, Emilie Macke, Isabelle Olivieri.

CE3C: Centre for Ecology, Evolution and Environmental Changes; Aquatic Biology, IRF Life Sciences, Science & Technology, KU-Leuven; Institut des Sciences de l'Evolution de Montpellier, Université Montpellier 2.

In haplodiploids, females pass their genes on to all their offspring, whereas a male's genes are only passed on to his daughters. Hence, males always benefit from female-biased sex ratios, whereas for females the optimal offspring sex ratio depends on the level of local mate competition (LMC), ranging from highly female-biased under strict LMC to unbiased in panmixia. This generates a sexual conflict over sex ratio, the intensity of which depends on the LMC level, with most intense conflict in panmixia. Such conflicts might lead to an evolutionary arms race, with persistence traits evolving in males and resistance traits in females. Although this prediction is theoretically straightforward, it remains untested empirically. We addressed this by crossing spider mites that evolved under varying intensities of LMC (hence of sexual conflict), to mates from inbred lines. Under high levels of sexual conflict, both sexes evolved manipulative traits to shift the sex ratio to their own advantage. In females, this was partly achieved through changes in egg size. We thus show that (a) LMC levels modulate sexual conflict over sex ratio in haplodiploids, driving the evolution of manipulative traits and (b) fathers can affect sex ratio, challenging conventional assumptions.

**Male Drosophila melanogaster fight more, and sire shorter-lived daughters, when rival male are unrelated and unfamiliar (51991)**

**Pau Carazo**, Jennifer Perry, Fern Johnson, Tommaso Pizzari, Stuart Wigby.

University of Valencia; University of Oxford.
Competition over access to reproductive opportunities can lead males to harm females. Recent inclusive fitness theory predicts that in structured populations male harm of females may be reduced when local male competitors are related. Previous empirical work has presented evidence consistent with this prediction in the fruit fly, Drosophila melanogaster. Here we explore the consequences of relatedness amongst rival males for the next generation. We show that groups of unrelated-unfamiliar (i.e. raised apart) males fight more intensely than groups of related-familiar (i.e. raised together) males, consistent with previous findings, and that exposure to a female is required to trigger kin-biased male-male competition. We further show that differences in male-male competition are associated with transgenerational effects: when daughters where themselves exposed to males, daughters of females exposed to unrelated males suffered higher mortality than the daughters of females exposed to related males. Collectively, these results support the hypothesis that within-male group relatedness and/or familiarity can modulate male-male competition with important transgenerational consequences.

# How sex-biased dispersal affects the resolution of intralocus sexual conflict (52922)

Bram Kuijper, Rufus A. Johnstone.

*Department of Genetics Evolution and Environment, University College London, UK; CoMPLEX, Centre for Maths & Physics in the life sciences, University College London, UK; Department of Zoology, University of Cambridge.*

Classical models on intralocus sexual conflict assume large and well-mixed populations, raising the question whether predictions extend to structured populations with interacting relatives. Here we present a model of intralocus sexual conflict in a spatially structured population with sex-biased dispersal. Strikingly, we find that sexually antagonistic traits that are beneficial to females (and detrimental to males) predominate in populations with female-biased dispersal, while male-beneficial traits prevail in populations with male-biased dispersal. For the case where females are the more dispersing sex, this can be explained by noting that philopatric males are more related than dispersing females to any juveniles in the local patch. Hence, in dying, males are more likely to be replaced by relatives than females, so that the effective cost of expressing a detrimental sexually antagonistic trait is lower for males than females. As a result of reduced selection in males, the trait evolves towards the female rather than the male optimum. In the presence of mating skew, a similar principle holds, which causes characters to evolve towards the optimum of the sex that endures the strongest competition for matings. Our findings show that the ecological context of sexual antagonism is more important than hitherto anticipated.

# Artiodactyl limb diversification: attenuated sensing of SHH by Ptch1 underlies adaptive evolution of bovine limbs (52537)
**Rolf Zeller**, Javier Lopez-Rios, Amandine Duchesne, Dario Speciale, Guillaume Andrey, Kevin A. Peterson, Carol Wicking, Andrew P. McMahon, Denis Duboule.

*University of Basel; INRA Genetique Animale et Biologie Integrative; EPFL Lausanne and
University of Geneva; University of Southern California; The University of Queensland.*

A fascinating aspect is to understand how basic and robust patterning processes are altered to allow diversification. For example, the pentadactylous blueprint of the limb skeleton has been modified extensively and allowed adaptation to different habits during tetrapod evolution. Cursorial animals such as artiodactyls have modified their distal limb skeleton for fast running by reduction and loss of digits in conjunction with assuming unguligrade posture.

Molecular analysis of mouse and bovine limb development reveals the progressive loss of anterior-posterior polarity in bovine limb buds. These alterations are caused by a failure to up-regulate Ptch1 expression in the bovine limb bud mesenchyme, which renders the progenitors insensitive to graded SHH signaling. Functional genomics identified a cis-regulatory module (CRM) within the Ptch1 locus that controls expression in the mouse limb bud mesenchyme.

Strikingly, the orthologous bovine sequences are unable to activate expression in transgenic mouse embryos, establishing that the bovine CRM has degenerated. In fact, genetic inactivation of Ptch1 in the mouse limb mesenchyme phenocopies molecular differences seen in bovine and pig limb buds. Currently, we are investigating if a microsatellite expansion in the CRM region of all artiodactyls contributes to its functional degeneration in Bovidae and other artiodactyls such as Suidae.

Session 1 WED POL D 33

Selection on flower colour in snapdragon hybrid zones (52539)

**David Field**, Hugo Tavares, Enrico Coen, Nick Barton.

*IST Austria; John Innes Centre.*

A major goal of evolutionary biology is to understand how diverging populations become distinct species. Much progress has been made in characterising genomic differentiation and the genes that contribute towards phenotypic differences and reproductive isolation. However, directly linking genes to phenotypes to fitness and reproductive isolation in nature has proved challenging. We address this gap in a uniquely tractable plant system, Antirrhinum (snapdragons). In this system, two subspecies with different flower colour give rise to four hybrid phenotypes across narrow hybrid zones. Flower colour is under simple genetic control, allowing us to track individuals, their phenotypes and underlying genes through space and time. Whole genomes sampled across the hybrid zone show the highest regions of genomic differentiation are located around the genes that control flower colour. The existence of steep clines for flower colour and diagnostic SNPs linked to the underlying genes indicates selection against some recombinant phenotypes. A detailed multi-generational pedigree is used to directly measure the reproductive success of the major phenotypes and determine the fitness landscape for interacting flower colour genes. By linking divergent genomic regions to phenotypic traits and how they directly influence fitness in nature, we provide an integrated understanding of the speciation process.
# Adaptation to a special environment: a novel endosymbiotic bacterium living inside an ant (52725)

**Antonia Klein**, Lukas Schrader, Rosario Gil, Alejandro Manzano-Marín, Laura Flórez, Martin Kaltenpoth, Amparo Latorre, Andrés Moya, Jan Oettler.

*Institute of Zoology/Evolutionary Biology, University Regensburg, Germany; Institut Canvanilles de Biodiversitat i Biologia Evolutiva, Universitat de Valencia, Spain; Max Planck Institute for Chemical Ecology, Jena, Germany.*

Bacteria are ubiquitous in nature and have evolved uncountable adaptations to the environment. For example, so called endosymbionts live inside eukaryotic hosts. Endosymbionts often evolve mutualistic associations with their hosts, where they provide novel ecological traits to the host and in return are maintained in a sheltered environment. We discovered a novel intracellular bacterial symbiont of the invasive ant Cardiocondyla obscurior, 'Candidatus Westeberhardia cardiocondylae' and provide a first characterization of its association with the ant host. Westeberhardia shows substantial genome reduction, a typical feature of endosymbionts. Metabolic pathway analyses of the Westeberhardia genome, localization of Westeberhardia via FISH in bacteriomes and an increase of the symbiont in the pupal stage, suggest provisioning with tyrosine precursors during metamorphosis for the host's cuticle built up as the basis of the mutualism. After hatching of the host the gut-associated bacteriomes degrade but queens maintain Westeberhardia in their ovaries for vertical transmission, whereas bacterial populations in adult workers and males degenerate with age. With the discovery of a naturally symbiont-free host population we have discovered a suitable system for studying ant-bacteria co-adaptation in the future.

# The hemoglobin repertoire in the order of Gadiformes linked to depth adaptation (52770)

**Helle Tessand Baalsrud**, Ole Kristian Tørresen, Martin Malmstrøm, Walter Salzburger, Kjetill Sigurd Jakobsen, Sissel Jentoft.

*University of Oslo; University of Basel.*

Gene and genome duplications can promote evolutionary invention by releasing the copied genetic region from functional constraints. Natural selection acting on the new gene can result in sub-/neofunctionalization or gene loss. In teleosts, the number of hemoglobin genes varies extensively between and within lineages. This observed phenomenon is likely driven by natural selection as environmental factors such as temperature and oxygen partial pressure, which in turn depends on water depth, influence the oxygen carrying properties of hemoglobin. In the order of Gadiformes (cods and allies), species have adapted to an array of ocean depths, and it has been hypothesized that the ancestor originated from a deep-water
fish.

Here we use whole genome sequencing of 27 species to characterize the hemoglobin repertoire across this lineage. By using ancestral reconstruction and tests of natural selection we unveil that hemoglobin may have been key for the evolutionary transition from a deep-water fish to a diversity of species occupying the entire water-column, and could be involved in ecological speciation in this lineage.

# Molecular structure and functional diversity of a naturally polymorphic enzyme: PGI of Colias (52771)

Jason Hill, Ward Watt.

*Stockholm University; University of South Carolina.*

Reproductive success in flying insects is heavily dependent on an effective core metabolic pathway, glycolysis, in responding to rapidly fluctuating energy demands. The glycolytic enzyme phosphoglucose isomerase, PGI, is extensively polymorphic in Colias (Lepidoptera, Pieridae), and its polymorphs' genotypic functional differences successfully predict performance and fitness differences in the wild. The structural basis for this functional diversity has not been studied directly until now. We produced a high-resolution crystal structure for Colias PGI, and then used that native structure as a template to carry out 50 nanosecond molecular dynamics simulations for different allozymes of PGI. These simulations were coupled with enzyme kinetics measurements of catalytic function and thermal stability in an attempt to match structural differences between the allozymes with biochemically measured functional differences. Kinetics analysis confirmed the already known tradeoff in thermal stability vs. catalytic function in homodimers that maintains polymorphism within species and has identified the most likely mutational path between the fixed difference that separates the alpine C. medii and lowland C. eurytheme.

# The genetic basis of parallel speciation in a marine snail (52944)

Anja Marie Westram, Marina Panova, Juan Galindo, Roger Butlin.

*University of Sheffield; University of Gothenburg; University of Vigo.*

Parallel divergence can provide strong evidence for the role of divergent selection. However, despite parallel phenotypic evolution, loci potentially affected by selection ('outlier loci') are often not shared among geographical locations, suggesting different underlying molecular mechanisms. Alternatively, low sharing might emerge if many outliers are spurious. Low outlier sharing has e.g. been observed in the marine snail Littorina saxatilis, which has evolved two ecotypes - adapted to wave exposure vs. crab predation - repeatedly in Sweden,