bluuebunny/crossref_metadata_2025_split huggingface dataset:
Variation in natural selection for growth and phlorotannins in the brown alga Fucus vesiculosus
Authors: Jormalainen V. , Honkanen T. 
Published: June 2004

Abstract
Directional selection for plant traits associated with resistance to herbivory tends to eliminate genetic variation in such traits. On the other hand, balancing selection arising from trade-offs between resistance and growth or spatially variable selection acts against the elimination of genetic variation. We explore both the amount of genetic variation and variability of natural selection for growth and concentration of phenolic secondary compounds, phlorotannins, in the brown alga Fucus vesiculosus. We measured variation in selection at two growing depths and two levels of nutrient availability in algae that had faced two kinds of past growing environments. Genetic variation was low for growth but high for phlorotannins. The form and strength of selection for both focal traits depended on the past growing environment of the algae. We found strong directional selection for growth rate in algae previously subjected to higher ultraviolet radiation, but not in algae previously subjected to higher nutrient availability. Stabilizing selection for growth occurred especially in the deep growing environment. Selection for phlorotannins was generally weak, but in some past-environment–current-environment combinations we detected either directional selection against phlorotannins or stabilizing selection. Thus, phlorotannins are not selectively neutral but affect the fitness of F. vesiculosus. In particular, there may be a fitness cost of producing phlorotannins, but the realization of such a cost varies from one environment to another. Genetic correlations between selective environments were high for growth but nonexistent for phlorotannins, emphasizing the high phenotypic plasticity of phlorotannin production. The highly heterogeneous selection, including directional, stabilizing, and spatially variable selection as well as temporal change in selection due to responses to past environmental conditions, probably maintains a high amount of genetic variation in phlorotannins. Such variation provides the potential for rapid evolutionary response of phlorotannins under directional selection.
Condition-dependent traits and the capture of genetic variance in male advertisement song
Authors: Brandt L. S. E. , Greenfield M. D. 
Published: June 2004

Abstract
The occurrence of additive genetic variance (VA) for male sexual traits remains a major problem in evolutionary biology. Directional selection normally imposed by female choice is expected to reduce VA greatly, yet recent surveys indicate that a substantial amount remains in many species. We addressed this problem, also known as the ‘lek paradox’, in Achroia grisella (Lepidoptera: Pyralidae), an acoustic moth in which males advertise to females with a pulsed ultrasonic song. Using a standard half-sib/full-sib breeding design, we generated F1 progeny from whom we determined VA and genetic covariance (COVA) among seven traits: three song characters, an overall index of song attractiveness, nightly singing period, adult lifespan, and body mass at adult eclosion. Because A. grisella neither feed nor drink as adults, the last trait, eclosion body mass, is considered a measure of ‘condition’. We found significant levels of VA and narrow-sense heritabilities (h2) for all seven traits and significant genetic correlations (= COVAi,j /√(VA i·VA j)) between most pairs of traits (i, j). Male attractiveness was positively correlated with body mass (condition), adult lifespan, and nightly singing period, which we interpret as an energy constraint preventing males in poor condition from singing attractively, from singing many hours per night, and from surviving an extended lifespan. The positive genetic correlation (r = 0.79) between condition and attractiveness, combined with significant levels of VA for both traits, indicates that much of the variation in male song can be explained by VA for condition. Finally, we discuss the morphological and physiological links between condition and song attractiveness, and the ultimate factors that may maintain VA for condition.
Behavioural interactions, kin and disease susceptibility in the bumblebee Bombus terrestris
Authors: Mallon Eamonn B. , Schmid-Hempel Paul 
Published: June 2004

Abstract
Behavioural interactions are often analysed in terms of their costs and benefits to the actors [Hamilton, (1964) J. Theor. Biol.7 1–16; Gadagkar, (1993) Trends Ecol. Evol.8 232–234; Foster et al., (2001) Ann. Zool. Fenn.38 229–238]. Using the bumblebee Bombus terrestris, we wish to distinguish between two possible determinants of interaction behaviour between conspecifics, namely kin-directed behaviour that reflects genetic distance between individuals, or, alternatively, interactions guided by a functional distance between individuals, specifically, with respect to disease susceptibility. We find no relationship between contact rate of individuals and the genetic distance of their respective colonies. Interestingly, we do find a significant negative correlation between contact rate and the distance between the two colonies in susceptibility to a spectrum of parasite strains. This cannot be explained by either of the a priori alternatives so we propose two further testable hypotheses to explain our results.
Phenotypic correlations among fitness and its components in a population of the housefly
Authors: Reed D. H. , Bryant E. H. 
Published: June 2004

Abstract
An individual's or a population's fitness is the result of a large number of interacting life history traits and the environment. Little information is available on the phenotypic correlations among fitness components and fitness itself, especially outside of Drosophila melanogaster. We also lack detailed information on trade-offs among life history traits. Here we present the relationship between adult progeny production and eight components of fitness, as well as some observed trade-offs between life history traits in the housefly (Musca domestica). We briefly discuss some of the ramifications of these relationships.
The cost of immunity in the yellow fever mosquito, Aedes aegypti depends on immune activation
Authors: Schwartz A. , Koella J. C. 
Published: June 2004

Abstract
Although host immunity offers the obvious benefit of reducing parasite infection, it is often traded-off with other fitness components. We investigated whether the cost of an immune response in the yellow fever mosquito, Aedes aegypti, is modulated by the antigen that activates the melanization immune response. Thus, one of three different novel antigens were injected into the mosquito's thorax – either a glass bead, a negatively charged (C-25) Sephadex bead, or a neutral (G-25) Sephadex bead – and fecundity and bead melanization were observed. Glass beads are immunologically inert and were therefore used as an inoculation control. The fecundity of mosquitoes inoculated with these beads did not differ from the fecundity of mosquitoes that did not melanize negatively charged or neutral beads. The ability of A. aegypti to melanize negatively charged Sephadex beads was associated with reduced fecundity, showing a clear cost of immunity. In contrast, melanization of the neutral beads was quite strong but had no effect on fecundity. Thus, the cost of what appeared to be the same immune response – melanization of a bead – depended on the type of bead that stimulated the immune system. Such differences might help to explain variation of immune efficacy against different parasites in natural populations.
Swift laboratory thermal evolution of wing shape (but not size) inDrosophila subobscuraand its relationship with chromosomal inversion polymorphism
Authors: Santos M. , Iriarte P.F. , Céspedes W. , Balanyà J. , Fontdevila A. , Serra L. 
Published: June 2004

AbstractLatitudinal clinal variation in wing size and shape has evolved in North American populations of Drosophila subobscura within about 20 years since colonization. While the size cline is consistent to that found in original European populations (and globally in other Drosophila species), different parts of the wing have evolved on the two continents. This clearly suggests that ‘chance and necessity’ are simultaneously playing their roles in the process of adaptation. We report here rapid and consistent thermal evolution of wing shape (but not size) that apparently is at odds with that suggestion. Three replicated populations of D. subobscura derived from an outbred stock at Puerto Montt (Chile) were kept at each of three temperatures (13, 18 and 22 °C) for 1 year and have diverged for 27 generations at most. We used the methods of geometric morphometrics to study wing shape variation in both females and males from the thermal stocks, and rates of genetic divergence for wing shape were found to be as fast or even faster than those previously estimated for wing size on a continental scale. These shape changes did not follow a neat linear trend with temperature, and are associated with localized shifts of particular landmarks with some differences between sexes. Wing shape variables were found to differ in response to male genetic constitution for polymorphic chromosomal inversions, which strongly suggests that changes in gene arrangement frequencies as a response to temperature underlie the correlated changes in wing shape because of gene-inversion linkage disequilibria. In fact, we also suggest that the shape cline in North America likely predated the size cline and is consistent with the quite different evolutionary rates between inversion and size clines. These findings cast strong doubts on the supposed ‘unpredictability’ of the geographical cline for wing traits in D. subobscura North American colonizing populations.
Extinction of the acoustic startle response in moths endemic to a bat-free habitat
Authors: Fullard J. H. , Ratcliffe J. M. , Soutar A. R. 
Published: June 2004

Abstract
Most moths use ears solely to detect the echolocation calls of hunting, insectivorous bats and evoke evasive flight manoeuvres. This singularity of purpose predicts that this sensoribehavioural network will regress if the selective force that originally maintained it is removed. We tested this with noctuid moths from the islands of Tahiti and Moorea, sites where bats have never existed and where an earlier study demonstrated that the ears of endemic species resemble those of adventives although partially reduced in sensitivity. To determine if these moths still express the anti-bat defensive behaviour of acoustic startle response (ASR) we compared the nocturnal flight times of six endemic to six adventive species in the presence and absence of artificial bat echolocation sounds. Whereas all of the adventive species reduced their flight times when exposed to ultrasound, only one of the six endemic species did so. These differences were significant when tested using a phylogenetically based pairwise comparison and when comparing effect sizes. We conclude that the absence of bats in this habitat has caused the neural circuitry that normally controls the ASR behaviour in bat-exposed moths to become decoupled from the functionally vestigial ears of endemic Tahitian moths.
Sources of stochasticity in models of sex allocation in spatially structured populations
Authors: Proulx S. R. 
Published: June 2004

Abstract
There are many ways to include stochastic effects in models of sex allocation evolution. These include variability in the number of mating partners and fecundity in a rich literature that goes back 20 years. The effects of variance in the fecundity and number of mating partners have typically been considered separately from the stochastic effects of mortality. However, I show that these processes produce mathematically equivalent models with subtly different biological details. These scenarios differ in the way that information becomes available to individuals because the parents often have information on mating partners while they are making sex allocation decisions, but must make these decisions before brood mortality takes place. This makes it possible to test which mechanism, stochastic mortality or variation in mating partners, is responsible for observed sex ratios. Alternatively, asymmetric variance between sexual functions can cause skewed sex allocation, even in the absence of local mate competition. This allows the evolution of either female- or male-biased sex ratios depending on which sexual function is more variable.
Experimental reduction of codon bias in the Drosophila alcohol dehydrogenase gene results in decreased ethanol tolerance of adult flies
Authors: Carlini David B. 
Published: June 2004

Abstract
The ethanol tolerance of adult transgenic flies of Drosophila containing between zero and ten unpreferred synonymous mutations that reduced codon bias in the alcohol dehydrogenase (Adh) gene was assayed. As the amino acid sequences of the ADH protein were identical in the four genotypes assayed, differences in ethanol tolerance were due to differences in the abundance of ADH protein, presumably driven by the effects of codon bias on translational efficiency. The ethanol tolerance of genotypes decreased with the number of unpreferred synonymous mutations, and a positive correlation between ADH protein abundance and ethanol tolerance was observed. This work confirms that the fitness effects of unpreferred synonymous mutations that reduce codon bias in a highly expressed gene are experimentally measurable in Drosophila melanogaster.
Evolution of eusociality and the soldier caste in termites: a validation of the intrinsic benefit hypothesis
Authors: Roux E. A. , Korb J. 
Published: June 2004

Abstract
In termites the evolution of reproductive altruism is not based on a particularly high relatedness between nestmates. For the evolution and maintenance of the ancestral sterile soldier caste, the benefits generated by the soldiers’ presence must compensate the loss of the soldiers’ reproductive potential. To study the impact of soldiers on colony's fitness, we manipulated the proportion of soldiers to nonsoldiers in colonies of the dry-wood termite Cryptotermes secundus.‘Soldier-less’ colonies were obtained by removing soldiers and inhibiting their development with an extract of soldier heads. The colonies were set up for 1 year in experimental nests in the field. ‘Soldier-less’ colonies produced fewer soldiers. The reduction of soldiers neither affected colony survival nor helper growth, but fewer dispersing sexuals were produced in ‘soldier-less’ than in control colonies. This confirms what was only supposed so far, that in termites soldiers are maintained for their intrinsic benefit to cost ratio.
Relatedness affects competitive performance of a parasitic plant (Cuscuta europaea) in multiple infections
Authors: Puustinen S. , Koskela T. , Mutikainen P. 
Published: June 2004

AbstractTheoretical models predict that parasite relatedness affects the outcome of competition between parasites, and the evolution of parasite virulence. We examined whether parasite relatedness affects competition between parasitic plants (Cuscuta europaea) that share common host plants (Urtica dioica). We infected hosts with two parasitic plants that were either half-siblings or nonrelated. Relative size asymmetry between the competing parasites was significantly higher in the nonrelated infections compared to infections with siblings. This higher asymmetry was caused by the fact that the performance of some parasite genotypes decreased and that of others increased when grown in multiple infections with nonrelated parasites. This result agrees with the predictions of theories on the evolution of parasite virulence: to enhance parasite transmission, selection may favour reduced competition with genetically related parasites in hosts infected by several genotypes. However, in contrast to the most common predictions, nonrelated infections were not more virulent than the sibling infections.
‘Anti-bee’ and ‘pro-bird’ changes during the evolution of hummingbird pollination in Penstemon flowers
Authors: Castellanos M. C. , Wilson P. , Thomson J. D. 
Published: June 2004

Abstract
Floral phenotypes may be as much the result of selection for avoidance of some animal visitors as selection for improving the interaction with better pollinators. When specializing on hummingbird-pollination, Penstemon flowers may have evolved to improve the morphological fit between bird and flower, or to exclude less-efficient bees, or both. We hypothesized how such selection might work on four floral characters that affect the mechanics of pollen transfer: anther/stigma exsertion, presence of a lower corolla lip, width of the corolla tube, and angle of flower inclination. We surgically modified bee-pollinated P. strictus flowers changing one trait at a time to make them resemble hummingbird-pollinated P. barbatus flowers, and measured pollen transfer by bumblebees and hummingbirds. Results suggest that, apart from ‘pro-bird’ adaptations, specific ‘anti-bee’ adaptations have been important in shaping hummingbird-flowers. Moreover, some trait changes may have been selected for only if changing in concert with other traits.
High dose refuge strategies and genetically modified crops – reply to Tabashnik et al.
Authors: Vacher C. , Bourguet D. , Rousset F. , Chevillon C. , Hochberg M. E. 
Published: June 2004

Abstract
Cultivating non-toxic conventional crops (refuges) in the proximity to transgenic crops that produce Bacillus thuringienesis (Bt) toxins is widely recommended to delay pest adaptation to these toxins. Using a spatially structured model of resistance evolution, Vacher and co-workers (Vacher, C., Bourguet, D., Rousset, F., Chevillon, C. & Hochberg, M.E. 2003. J. Evol. Biol.16: 378–387.) show that the percentage of refuge fields required for the sustainable control of pests can be reduced through intermediate levels of refuge field aggregation and by lowering the toxin dose produced by Bt plants. Tabashnik, B.E., Gould, F. & Carrière, Y. (2004 J. Evol. Biol doi: 10.1111/j1420–9101.2004.00695.x) call into question the results of Vacher et al. (2003) concerning the effect of toxin dose. They argue that these results arise from invalid assumptions about larval concentration–mortality responses for the insect considered, the cotton pest Heliothis virescens. We show here that the models presented by Vacher et al. (2003) and Tabashnik et al. (2004) both show inaccuracies in their definitions of genotypic fitness. The level of dominance estimated by Tabashnik et al. (2004) from larval mortality rates data is irrelevant to resistance evolution, and the fitness cost of resistance evolution, and the fitness cost of resistance is inaccurately integrated into their framework. Neverthless, the comments of Tabashnik et al. (2004) are very helpful in elucidating the definitions of genotypic fitness used in Vacher et al. (2003) and in pointing out the essential factors in predicting the evolution of insect resistance to Bt transgenic crops, namely, accurate estimations of the fitness cost of resistance, of the dominance level of this cost, and of the variations in the dominance level of the advantage conferred by the resistance with Bt toxin dose.
The interaction between reproductive lifespan and protandry in seasonal breeders
Authors: Morbey Y. E. , Abrams P. A. 
Published: June 2004

Abstract
The timing and duration of reproductive activities are highly variable both at the individual and population level. Understanding how this variation evolved by natural selection is fundamental to understanding many important aspects of an organism's life history, ecology and behaviour. Here, we combine game theoretic principles governing reproductive timing and the evolutionary theory of senescence to study the interaction between protandry (the earlier arrival or emergence of males to breeding areas than females) and senescence in seasonal breeders. Our general model applies to males who are seeking to mate as frequently as possible over a relatively short period, and so is relevant to many organisms including annual insects and semelparous vertebrates. The model predicts that protandry and maximum reproductive lifespans should increase in environments characterized by high survival and by a low competitive cost of maintaining the somatic machinery necessary for survival. In relatively short seasons under these same conditions, seasonal declines in the reproductive lifespans of males of equivalent quality will be evolutionarily stable. However, over a broad range of potential values for daily survival and maintenance cost, reproductive lifespan is expected to be relatively short and constant throughout a large fraction of the season. We applied the model to sockeye (or kokanee) salmon Oncorhynchus nerka and show that pronounced seasonal declines in reproductive lifespan, a distinctive feature of semelparous Oncorhynchus spp., is likely part of a male mating strategy to maximize mating opportunities.
Hybridization and regional sex ratios in Nemophila menziesii
Authors: Barr C. M. 
Published: June 2004

Abstract
I tested whether a region of high female frequencies in the gynodioecious plant, Nemophila menziesii, may be due to hybridization between regionally distributed populations with different corolla colours. I crossed plants in the greenhouse from populations with different corolla colours and found that hybrid crosses yielded higher frequencies of females than within-colour crosses. In the field, I found that populations with high female frequencies had intermediate mean corolla colours and higher variance in corolla colour, two traits suggesting hybridization. Nemophila menziesii has nuclear–cytoplasmic sex inheritance, thus if populations with different corolla colours are fixed for different male-sterile cytoplasms and matching nuclear restorer alleles, hybridization between populations with different corolla colour should yield high frequencies of females. Two populations that are all hermaphroditic in the field segregated females in hybrid crosses suggesting that field populations may contain sex ratio distorters but appear undistorted, a prediction of genomic conflict theory.
Interspecific aggression and character displacement in the damselfly Calopteryx splendens
Authors: Tynkkynen K. , Rantala M. J. , Suhonen J. 
Published: June 2004

Abstract
Problems in species recognition are thought to affect the evolution of secondary sexual characters mainly through avoidance of maladaptive hybridization. Another, but much less studied avenue for the evolution of sexual characters due to species recognition problems is through interspecific aggression. In the damselfly, Calopteryx splendens, males have pigmented wing spots as a sexual character. Large-spotted males resemble males of another species, Calopteryx virgo, causing potential problems in species recognition. In this study, we investigate whether there is character displacement in wing spot size and whether interspecific aggression could cause this pattern. We found first that wing spot size of C. splendens in populations decreased with increasing relative abundance of C. virgo. Secondly, C. virgo males were more aggressive towards large- than small-spotted C. splendens males. Thirdly, in interspecific contests C. virgo males had better territory holding ability than C. splendens males. These results suggest that interspecific aggression may have caused character displacement in wing spot size of C. splendens, because the intensity of aggression towards large-spotted males is likely to increase with relative abundance of C. virgo males. Thus, interspecific aggression may be an evolutionarily significant force that is able to cause divergence in secondary sexual characters.