bluuebunny/crossref_metadata_2025 huggingface dataset:
Parental control of sex ratio in Gammarus duebeni, an organism with environmental sex determination
Authors: Watt Penelope J.
Published: December 2004

Parental sex ratio control was investigated in Gammarus duebeni, an amphipod with an environmentally mediated sex determining system. The effect on the F2 generation sex ratio of the photoperiodic conditions experienced by a) the P generation during and after copulation, b) the F1 generation before and after sex determination, and c) the F2 generation themselves during the period of sex determination, was tested. The photoperiodic conditions the F2 generation experienced during the period of sex determination had a significant effect on their sex ratio (more males were produced under long‐day than under short‐day conditions), but the photoperiodic conditions experienced by the F1 generation males and females or the P generation on the F1 male's side had no effect on the F2 sex ratio. However, the photoperiodic conditions the P generation on the F1 female's side experienced significantly affected the F2 sex ratio. When these animals experienced long‐day conditions the F2 generation became female biased and when they experienced short‐day conditions, male biased. It is proposed that the mechanism of control operates through the F1 generation mothers whilst in an embryonic stage of development in the P generation mother's brood pouch. The photoperiodically mediated effects of the embryonic F1 generation mother and the F2 generation on sex determination are additive. A mechanism by which both F1 generation maternal and F2 generation sex ratio control could operate in the field is proposed.
Comparison of molecular and paleontological data in diatoms suggests a major gap in the fossil record
Authors: Philippe Hervé , Sörhannus Ulf , Baroin Anne , Perasso Roland , Gasse Françoise , Adoutte André
Published: December 2004

Diatoms, unicellular eukaryotic algae with a siliceous skeleton, offer the rare advantage of displaying both an extensive fossil record and numerous extant species, thus providing the opportunity of confronting molecular and paleontological data in a protist group. A portion of the 28S ribosomal RNA was sequenced from 5 diatoms, the divergence times of which are well known. The nucleotide substitution rate was estimated in these unicellular eukaryotes and compared with the rate of multicellular eukaryotes, using a broad data base comprising metazoans and metaphytes. When using fossil record derived divergence times, our results show that the nucleotide substitution rate is about 5 times faster in diatoms than in chordates. But, when using the relative rate test, it is observed that, over a long time period, the nucleotide substitution rate may in fact have been slightly slower in diatoms than in chordates. For this contradiction, two possible explanations are proposed: (i) a failure of the relative rate test, (ii) a gap in the pre‐Jurassic diatom fossil record. We have checked that our results concerning the relative rate test were valid. Thus, the second hypothesis, which implies pre‐Jurassic diatom evolution, in fact already suggested by some non‐molecular evidences, is favoured. Decoupling of morphological differentiation from genetic speciation also appears to have occurred and may account in part for the underestimation of the dates of recent cladogenesis events.
Sexual isolation in Drosophila. II. Intraspecific variation in mate recognition systems
Authors: Marín Ignacio
Published: December 2004

A simple behavioral model is used to investigate whether differences in the specific‐mate‐recognition system (SMRS), occur within species of the Drosophila genus. This model takes into account, and overcomes, the distorting effect of vigor differences on experimental results. Analysis shows significant deviations from the expected values under the assumption of identical SMRSs in around one fifth of the multiple‐choice experiments performed with natural strains of twelve different Drosophila species. Different selection procedures raise the number of significant assortative mating results between strains of D. melanogaster and D. pseudoobscura from 3.0% to 32.8%. Finally, sub‐ or semispecific taxa show variations in their SMRS even more frequently (74.5%). Differences in male vigor and female receptivity are also found. These results show that a classification of Drosophila species based on SMRS stability, as proposed by the “Recognition concept of species”, is virtually impossible.
Habitats, stress, and evolutionary rates
Authors: Parsons P. A.
Published: December 2004

Habitats of organisms are expressed as an interaction between stress intensity, magnitude of environmental fluctuations, and energy availability from resources. Under this model organisms should evolve broad biological properties defined by such physical characteristics. When energy is severely restricted under the continuing constant stress of adversity‐selection, or in widely fluctuating and highly stressful environments, little evolutionary change is expected; relict species and ‘living fossils’ are the respective expectations. In rather stable abiotic environments where resources are limited habitat preferences may develop leading to specialization and ultimately adaptive radiations. On the other hand major new innovations are more likely in highly disturbed resource‐rich habitats. Evidence from the living and fossil biota is presented which is consistent with these conclusions.
Evolution in natural and experimental populations of Amphicarpaea bracteata
Authors: Parker Matthew A.
Published: December 2004

Genetically divergent lineages (biotypes) often coexist within local populations of the selfing annual Amphicarpaea bracteata (Leguminosae). At one site, a rapid change in lineage frequency was observed, with one biotype decreasing from 41% to 16% of the population over a 2 year period. During 6 additional years of censuses, this lineage showed no tendency to recover to its former abundance. An experimental population was constructed with approximately equal numbers of individuals from the two dominant biotypes in this population, and plants were allowed to grow and reproduce without interference for 3 generations. The same lineage that declined in the natural habitat was also strongly selected against in this experimental population, with a selection coefficient (0.57 per generation) comparable to that inferred from the initial decline in frequency of this lineage in nature (0.47). A greenhouse experiment suggested that differential adaptation to high vs. low light environments could be one factor affecting relative success of these lineages. Differences in reproductive allocation and disease resistance to local pathogens are also key factors likely to affect relative fitness. Overall, these results show that the genetic structure of selfing plant populations can be highly dynamic, with intense selection and sudden shifts in relative abundance of different lineages.
Origin of the crustacean schizoramous limb: A re‐analysis of the duplosegmentation hypothesis
Authors: Zrzavý J. , Štys P.
Published: December 2004

Emerson and Schram's hypothesis of a duplosegmental origin of the crustacean schizoramous (biramous) limb is confronted with new data on the phylogeny of arthropods and their mechanisms of development. The hypothesis is considered to be falsified since (a) the cephalic segments of the crustaceans bear schizoramous limbs but still seem to be homologous to those of the hexapods; (b) the embryonic origin of crustacean segments, limbs, and neuromeres appears to be the same as in the hexapods; (c) no genetic mechanism allowing for duplosegmentation in the crustaceans seems to exist.
Cyclical environmental changes as a factor maintaining genetic polymorphism. 1. Two‐locus haploid selection
Authors: Kirzhner V. M. , Korol A. B. , Ronin Y. I.
Published: December 2004

To classify different types of cyclic selection, a measure of fitness disequilibrium was used, and a class of systems were considered where this measure has the same sign in all states (sign‐concordant environments). The necessary conditions for existence of a fixed point (considering any moment within the period as a referring one) are obtained for sign‐concordant systems. However, analytical study of such systems, in the case of selection for equal additive genes, and numerical testing of more general situations, allowed us to conclude that no polymorphism is possible. In the alternative class of sign‐concordant systems, polymorphism is possible. However, we found that global stability is an exception rather than a rule for sign‐nonconcordant systems. Massive numerical simulations of selection in a four‐state environment were made for cycle lengths in the range 8–28 and with evenly distributed selection coefficients. The proportion of polymorphic regimes ranged up to about 1.5%, and was dependent on the recombination rate between the loci. It should be stressed, that polymorphism maintenance in the haploid systems, when it is possible, can not be considered as an effect derived from constant selection, or be a result of any hidden form of heterozygous advantage. In other words, polymorphism stability is causally connected with environmental fluctuations. Equally important is that this effect of fluctuations is only possible because of recombination: in single locus systems haploid cyclical selection is unable to produce protected polymorphism.
Phenotypic variation, sexual reproduction and evolutionary population dynamics
Authors: Doebeli Michael
Published: December 2004

I studied the effects of introducing phenotypic variation into a well‐known single species model for a population with discrete, non‐overlapping generations. The phenotypes differed in their dynamic behaviour. The analysis was made under the assumption that the population was in an evolutionary stable state. Differences in the timing of the competitive impacts of the phenotypes on each other had a strong simplifying effect on the dynamics. This result could also be applied to competition between species. The effect of sexual reproduction on the dynamics of the population was analysed by assuming the simplest genetic model of one locus with two alleles. Sexual reproduction made the system much more stable in the (mathematical) sense that the number of attractors was reduced and their basins of attraction enlarged. In a dominant system sex tended to increase the frequency of the recessive allele, and in an overdominant system it induced gene frequencies of 1/2. Whether the attractors in the dominant system tended to be simpler or more complex than the attractors in the asexual system depended on the phenotype of the recessive homozygote. The overdominant sexual system tended to have simpler dynamics than the corresponding asexual population. A 2‐locus model was used to study whether sexuals can invade an asexual population and vice versa. One locus coded for sexual and asexual reproduction, while the other coded for the dynamics. Enhanced stability through sexual reproduction seemed to be the reason why there was a clear asymmetry favouring sex in this evolutionary context.
Nucleotide Polymorphism at the rp49 region of Drosophila subobscura: Lack of geographic subdivision within chromosomal arrangements in Europe
Authors: Rozas J. , Segarra C. , Zapata C. , Alvarez G. , Aguadé M.
Published: December 2004

Restriction‐site polymorphism at the rp49 gene region has been studied in 234 lines of Drosophila subobscura representing different gene arrangements for the O chromosome. The population surveyed (El Pedroso, Spain) was sampled four times in each of two consecutive years. The data indicate that the two chromosomal classes studied, O[ST] and O[3 + 4], are genetically differentiated in El Pedroso. Comparison of the present results with those previously obtained for two other populations further supports that, for a given chromosomal class, European populations are not genetically differentiated. This lack of differentiation at the rp49 region within O[ST] and within O[3 + 4] stands in contrast to the clear latitudinal clines found in Europe for these arrangements.
Antagonistic and reinforcing pleiotropy: a study of differences in development time in wing dimorphic insects
Authors: Roff Derek A.
Published: December 2004

Morphological dimorphisms are found in many different taxa. Wing dimorphism in insects, in which some individuals possess wings and associated flight muscles and are thus volant while others lack a functional flight apparatus and are thus flightless, is a typical example of such types of dimorphisms. It has been extensively studied and such studies have demonstrated that the volant form, although possessing the advantage of flight capability, suffers a fitness cost in a delay in the onset of reproduction after emergence into the adult form and a reduced fecundity. Previous comparative analyses have suggested that there is no consistent trend for development time (hatching to adult) to differ between the two morphs. The present study analyses the phenotypic and genetic correlations between development time and wing morph in the cricket Gryllus firmus. It is shown that the macropterous (volant) morph develops faster than the micropterous (flightless morph). This trade‐off is manifested at both thephenotypic and genetic level. Further, a comparative analysis shows that the same phenotypic trade‐off is generally found in other Orthopteran species so far studied, but in other orders the micropterous morph develops faster. Provided that the phenotypic trade‐off is genetically based, in the Orthoptera the fitness advantage of the earlier onset of reproduction in micropterous females is offset by the extended development time (antagonistic pleiotropy). However, in other orders there is reinforcing pleiotropy in that the micropterous females develop faster and reproduce sooner than the macropterous morph. These results highlight the complexity of fitness interactions and the need to study a phenomenon across several taxa.
Intrasexual selection and phylogenetic constraints in the evolution of sexual canine dimorphism in strepsirhine primates
Authors: Kappeler P. M.
Published: December 2004

The goals of this study were to analyze the origin and function of sex differences in the size of canine teeth among Malagasy lemurs and other strepsirhine primates. These analyses allowed me to illuminate interactions between different mechanisms of sexual selection and to elucidate constraints on this sexually‐selected trait. In contrast to central predictions of sexual selection theory, polygynous lemurs lack both sexual dimorphism in body size and male social dominance, but the degree of sexual dimorphism in the size of their canines is not known. A comparison of male and female canine size in 31 species of lemurs and lorises revealed significant male‐biased canine dimorphism in only 6 of 13 polygynous lemur species. This result is in contrast to predictions of a hypothesis that would explain the lack of size dimorphism in lemurs as a result of high viability costs because canine teeth presumably have low maintenance costs and because they are used as weapons in male‐male combat. Moreover, because females had significantly larger maxillary canines than males in only one lemur species, female dominance is not generally based on female physical superiority and selective forces favoring female dominance do not constrain sexual canine dimorphism in the sense of a pleiotropic effect. Contrary to predictions of sexual selection theory, species differences in canine dimorphism across strepsirhines were neither associated with differences in mating system, nor with the potential frequency of aggression. Variation in canine dimorphism was also unrelated to differences in body size, but there were significant differences among families, pointing to strong phylogenetic constraints. This study demonstrated that polygynous lemurs are at most subject to weak intrasexual selection on dental traits used in male combat and that traits thought to be under intense sexual selection are strongly influenced by phylogenetic factors.
Geographic variation in allozymes of populations of Salamandra salamandra (Amphibia: Urodela) exhibiting distinct reproductive modes
Authors: Alcobendas M. , Dopazo H. , Alberch P.
Published: December 2004

The populations of the urodele Salamandra salamandra in the Northern Iberian Peninsula exhibit very different coloration patterns and a remarkable range in reproductive modes (from giving birth to a large number of aquatic larvae to a parturition event of just a few fully metamorphosed, i.e. terrestrial, offspring). Electrophoretic study of geographic variation in allozymes shows that this extraordinary diversity, particularly in reproductive modes, is not accompanied by a genetic differentiation of similar magnitude. All the populations sampled along a transect crossing the Northern part of the Iberian Peninsula and encompassing the various reproductive strategies, as previously described, can be ascribed to a single species, because of small interpopulational genetic distances (ranging DNei from 0.05 to 0.199) and absence of fixed (diagnostic) alleles. A variety of phenetic and cladistic methods were used to elucidate the relationship among populations, based on allozyme data. These methods defined two well corroborated clusters: the first contains populations of salamanders with a blotched dorsal coloration pattern and characterized by parturition of aquatic larvae; the second group is composed of populations exhibiting a striped dorsal coloration pattern, smaller adult body size, and giving birth to fully metamorphosed terrestrial offspring. The latter group also encompasses some populations where mixed parturition events, which include both larvae and metamorphosed offspring, which have been recorded (Dopazo and Alberch, 1994). The absence of a correlation between genetic and geographic distance suggests that the mode of differentiation of the species is based on at least two successive events of isolation, radiation, and secondary contact between populations. Furthermore, the validity of the described “subspecies” is questioned by our data, which point out the need for a detailed systematic study of Salamandra from a global perspective. “Viviparity”, here meaning giving birth to fully metamorphosed offspring, originated once and occurs as intraspecific, and even as intrapopulational variation. Thus, we confirm a system where a major evolutionary innovation ‐the acquisition of independence from the aquatic media in the primitive amphibian complex life cycle‐, can be studied at the microevolutionary, i.e., intra‐ and inter‐populational level.
Evolution of sexual mimicry in sperm‐dependent all‐female forms of Poeciliopsis (Pisces: Poeciliidae)
Authors: Lima N. R. W. , Kobak C. J. , Vrijenhoek R. C.
Published: December 2004

The twofold advantage of all‐female reproduction is limited in many asexual lineages because females are sperm‐dependent. Males of a related sexual‐host species typically prefer conspecific females as mates. According to the “sexual mimicry” hypothesis, an all‐female lineage that closely resembles females of the sexual‐host species should have enhanced mating success. Examination of mating success in all‐female fish of the genus Poeciliopsis supported this hypothesis. The excellent sexual mimicry of some all‐female strains could have evolved through mutations within clonal lineages subsequent to their origins as interspecific hybrids. Alternatively, this mimicry may have been “frozen” from variation in the sexual gene pool when new unisexual lineages first arose. To test the latter hypothesis, we examined laboratory synthesized strains of the hybridogenetic fish P. monacha‐lucida. The frozen variation hypothesis was supported by the present results.
Genetic covariances within and between species: indirect selection for hybrid inviability
Authors: Johnson N. A. , Wade M. J.
Published: December 2004

Genotype‐environment interactions and natural selection can result in local specialization when different genotypes are favored in different environments. Restricted gene flow or genetic subdivision enhances local genetic diversification across a species when natural selection acts on such variation. The indirect evolution of reproductive isolation and the restriction of gene flow between species in statu nascendi may provide a central role for genotype‐environment interactions in speciation genetics. We derive the expected genetic covariance between heterospecific and conspecific viability fitness under several different models of selection, dominance, and breeding structure. Standard quantitative genetic methods can be used to estimate these covariances in experimental studies. These genetic covariances permit us to evaluate in a formal way the indirect effects of selection within a species on the evolution of hybrid inviability between species. We find that, for autosomal loci and random mating, the genetic covariance across species is equal to the product of three quantities: (1) the viability of the best hybrid genotype; (2) the viability effect of an allele in hybrids; and, (3) the change in allele frequency due to selection in the conspecific population. Inbreeding within the conspecific population, expressed as Wright's coefficient, F, increases the genetic covariance by a factor (1 + F). In all cases, a negative genetic covariance across species is evidence for hybrid inviability evolving as an indirect effect of selection within species for adaptive (as opposed to neutral) genetic change.

“It is an irony of evolutionary genetics, that although it is a fusion of Mendelism and Darwinism, it has made no direct contribution to what Darwin obviously saw as the fundamental problem: the origin of species…. While it is a question of elementary population genetics to state how many generations will be required for the frequency of an allele to change from q1 to q2, we do not know how to incorporate such a statement into speciation theory, in large part because we know virtually nothing about the genetic changes that occur in species formation.”

(Lewontin 1974, p. 159)
Measuring spatial variation in natural selection using randomly‐sown seeds of Arabidopsis thaliana
Authors: Stratton D. A. , Bennington C. C.
Published: December 2004

We describe a simple method of measuring spatial variation in fitness using randomly sown seeds. Given a random initial distribution of seeds, any spatial variation in the final distribution of genotypes must be the result of spatial variation in natural selection. Departures from spatial randomness are tested using a modification of join‐count statistics, based on the probability that two randomly chosen plants separated by a given distance carry the same genetic marker. Monte Carlo simulations showed that for the randomly sown seeds design the join‐count test had higher power to detect spatial variation in fitness than analysis of variance. The power was relatively independent of the number of genotypes used or the number of microsites sampled. The method was tested in the field using three standard lines of Arabidopsis thaliana. At the end of the life cycle, adjacent plants were significantly more likely to be the same line than randomly chosen pairs and the spatial dependence extended to distances of nearly 50 cm. Simple experiments like this may be especially useful for “comparative ecological genetics”, allowing systematic studies of natural selection among many species or habitats.
Sympatric and allopatric combinations of hen fleas and great tits: a test of the local adaptation hypothesis
Authors: Dufva R.
Published: December 2004

To test whether allopatric nest parasites differ from sympatric ones in their effect on various life history traits of their avian host, I designed a cross‐transfer experiment in which hen fleas (Ceratophyllus gallinae) were exchanged between great tit (Parus major) nests in two geographically widely separated areas. In neither of the areas did allopatric fleas influence body mass, tarsus length, wing length, duration of nestling period or mortality in great tit nestlings more severely than did sympatric fleas. Duration of incubation was also similar among females independent of experimental treatment. This lack of difference between allopatric and sympatric fleas is hypothesized to reflect the comparative harmlessness of hen fleas for their hosts.
Population structure and interdemic selection in the cooperative spider Anelosimus eximius
Authors: Smith D. R. , Hagen R. H.
Published: December 2004

The degree of relatedness among interacting individuals helps determine the fitness consequences of particular behaviors, whereas the partitioning (and amount) of genetic variation among and within groups controls the level at which selection will act most effectively. Three criteria are considered necessary for selection to act at the group or interdemic level: high rate of group initiation/extinction; differential survival and reproduction among groups; and highly subdivided population structure. The first two criteria have been demonstrated by earlier studies of Anelosimus eximius colonies. This study employs hierarchical analysis of allozyme polymorphisms to demonstrate the third criterion, subdivided population structure.

Anelosimus eximius
were collected from Suriname, Panama, Ecuador, Peru and Trinidad. Seven of 40 scorable enzyme loci revealed variation; 4 of these were polymorphic within colonies or regions. Expected heterozygosities were low, ranging from 0 (Ecuador, Peru) to ∼0.03 (Suriname). For each polymorphic locus, hierarchical
F
‐statistics were used to partition overall genetic variation into among‐region (or among‐population;
F
rt
), among‐colony (
F
sr
), and within‐colony (
F
is
) components. Samples from Suriname (43 colonies, 4 local populations) were the most informative; lack of scorable variation limited the inferences that could be drawn from other regions.
A. eximius
colonies are highly inbred: negative estimates of
F
is
imply very small effective colony sizes (∼6.5 for Suriname samples). By contrast, estimates of
F
sr
were very high: the mean for Suriname samples was 0.890, indicating neglibible gene flow among established colonies. Inbreeding within colonies, and genetic differentiation among colonies are consistent with demographic and behavioral observations of
A. eximius .

We suggest that interdemic selection is probable in this species and other cooperative spiders with this type of social system, and that mutual tolerance and absence of nest‐mate recognition, as well as female‐biased sex ratios, may have arisen by interdemic selection.
Parent‐offspring regression suggests heritable susceptibility to ectoparasites in a natural population of kittiwake Rissa tridactyla
Authors: Boulinier T. , Sorci G. , Monnat J.‐Y. , Danchin E.
Published: December 2004

Little information is available on the genetic variability of host susceptibility to parasites in natural populations despite its importance for the understanding of the evolution of host‐parasite interactions. A long‐term demographic and epidemiologic survey of a seabird population allowed us to investigate the potential correlation between parent and offspring ectoparasite load, while controlling for various environmental factors. In particular, parasite loads were measured for all individuals (i.e., parents and offspring) when they were nestlings and the effect of the year and breeding cliff were taken into account. The positive correlation found between parent and offspring parasite loads suggests a heritable susceptibility to ectoparasitism by ticks in this host population and that this character has the potential to respond to natural selection.
A genetic analysis of some components of reproductive isolation between two closely related species, Spodoptera latifascia (Walker) and S. descoinsi (Lalanne‐Cassou and Silvain) (Lepidoptera: Noctuidae)
Authors: Monti L. , Génermont J. , Malosse C. , Lalanne‐Cassou B.
Published: December 2004

The two closely related noctuid moths Spodoptera latifascia and S. descoinsi have been found in sympatry in some parts of French Guiana. They differ by i) ecological preferences, ii) some anatomical features of the genital tract, iii) the relative amounts of the two main components of the female pheromonal blend, and iv) the temporal pattern of sexual behaviour. Viable and fertile interspecific hybrids can be obtained in the laboratory, thus permitting a genetic study of some of these traits.

The anatomical differences cause perturbations in mating efficiency. Experimental results show that these differences are hereditarily transmitted, but their exact mode of inheritance remains unknown. The timing of initiation of female calling activity is very likely to be under polygenic control. Conclusive evidence showed that a pair of major autosomal alleles determined the pheromone composition. Moreover, some of the data suggest that the descoinsi allele would become lethal in certain mosaic latifascia/descoinsi genomic environments.

The ecological factor is likely to be the major component of reproductive isolation between the two species in natural conditions. However in contact zones, the differences in pheromone composition and in timing of sexual activity are probably involved in preventing interspecific hybridization.

Two speciation scenarios are proposed, both sympatric. In one of them, the primary event would be a fragmentation of the tropical forest followed by disruptive selection associated with habitat diversification. In the other, the speciation process might have been initiated by the occurrence of mutations acting on the pheromone mediated mate recognition system.
Variation in growth in the blue tit (Parus caeruleus)
Authors: Björklund M.
Published: December 2004

The pattern and amount of phenotypic and genetic variation in growth was analysed using the infinite‐dimensional model in natural populations of the blue tit (Parus caeruleus). A size‐index was used to analyse patterns of variation and covariation across ages (2, 5, 8, 11 and 14 days). Genetic variation was analysed using mother‐, father‐, and midparent‐offspring regressions in the blue tit. Phenotypic variation in growth was limited to a few dimensions only, while heritabilities were close to zero at all ages except at 2 days when a significant mother‐offspring relation was found. The phenotypic variance‐covariance matrix over ages was found to be singular, which suggests that there are trajectories for which there is no phenotypic variation, and which therefore they cannot evolve. The phenotypic growth trajectory associated with the largest amount of variation basically showed a high to moderately high covariation across ages. These results have macroevolutionary implications in terms of the outcome of selection which generally will be in terms of overall size changes but with a slow rate of change due to low heritabilities; an outcome consistent with macro‐evolutionary patterns of morphological variation in birds. A simulation study supported the conclusion that high covariances among traits and ages can impose considerable constraint on a microevolutionary scale.
Effects of pre‐dispersal selection on offspring growth and survival in Erythronium grandiflorum
Authors: Cruzan M. B. , Thomson J. D.
Published: December 2004

Effects of pre‐seed‐dispersal processes on offspring vigor were examined in Erythronium grandiflorum using manipulations of the number of pollen donors contributing to the pollen pool and comparisons of means and variances in offspring growth measurements. There were no effects of the number of donors on measures of pollen‐tube growth, ovule abortion, seed set, mean seed weight, or seedling germination. Seeds from pollinations with only one donor produced corms that averaged 5% lighter after one season of growth and had lower overall survival after three years compared to corms from pollinations with either three or ten donors. Patterns of within‐ and among‐family variance estimates for the different treatments were consistent with the hypothesis that less‐vigorous offspring were eliminated prior to seed dispersal in the multiple‐donor treatments. The difference in the growth of offspring from different treatments was apparently not due to pollen competition because pre‐zygotic attrition of pollen tubes led to incomplete fertilization of ovules. Results from this study suggest that post‐fertilization abortion of less‐vigorous progeny, perhaps as a consequence of early‐acting inbreeding depression, is responsible for the increase in the average vigor of offspring from multiply‐sired fruits.
Absence of direct sexual selection for parasitoid encapsulation in Drosophila melanogaster
Authors: Kraaijeveld A. R. , Emmett D. A. , Godfray H. C. J.
Published: December 2004

Resistance against parasites may play a role in female mate choice, especially if males that have actually survived parasitism can be discriminated from males that have not been parasitised. Larvae of several Drosophila species are subject to attack by hymenopteran parasitoids, but have the ability to kill the parasitoid egg through the process of encapsulation. Because an encapsulated egg remains visible in the abdomen of the adult fly throughout its life, its presence in a male signals to a female that the male has the genes to survive parasitism. The hypothesis that females preferentially mate with males bearing an encapsulated egg in their abdomen was tested using D. melanogaster. No indication was found for this female preference. The absence of preference for males with “good genes” could result from sensory constraints in the female or a negative correlation between encapsulation ability and some other fitness component. Alternatively, it is hypothesised that the black abdominal ends of the males of many species in the melanogaster‐group evolved to mimic encapsulated eggs, leading to the breakdown of capsule recognition by the female.
Selfing and outcrossing but no apomixis in two natural populations of diploid Potentilla argentea
Authors: Holm S. , Ghatnekar L. , Bengtsson B. O.
Published: December 2004

It has been suggested that diploid Potentilla argentea, hoary cinquefoil, is a facultative apomict. We have investigated the way such plants produce seeds under natural conditions in two populations from southern Sweden. About one hundred plants were studied cytometrically to ascertain their ploidy level. A standard population investigation based on two informative isozyme loci was then performed on the diploid plants. Finally, seeds were taken from heterozygous plants to determine the genetic constitution of their offspring. From the offspring analysis it followed that apomixis did not occur, at least not to any noticeable degree. From the population investigation it could be deduced that most seeds were produced by selfing.
Morphological variation in Plantago lanceolata L.: effects of light quality and growth regulators on sun and shade populations
Authors: Van Hinsberg A.
Published: December 2004

The effects of different ratios of red to far‐red light (R/FR‐ratio) and of exogenously applied growth regulators on the morphology of plants from sun and shade populations were studied. Large differences in growth form were found between populations adapted to either sun or shaded habitats. Low R/FR‐ratios, simulating vegetation shade, induced a growth form similar to that of plants from the shade population. High R/FR‐ratios, simulating sunlight, had the opposite effect. Most morphological differences between shade and sun populations and effects of low R/FR‐ratios on growth form could be mimicked by exogenously applied gibberellin (GA3). In contrast, application of a gibberellin inhibitor (CCC) induced a growth form similar to that of the sun population and of plants grown under a high R/FR‐ratio. Interactions between genetic background, the R/FR‐ratio, and hormone treatment, were small and the factors exerted their action independently. The results are discussed in relation to the influence of developmental constraints on the evolvability of optimal phenotypes and the plastic responses therein.
Optimum search speed and activity: a dynamic game in a three‐link trophic system
Authors: Leonardsson K. , Johansson F.
Published: December 2004

We analysed how a consumer should simultaneously trade‐off search speed and time active in a game with predators that optimise their search speed. Both the consumers and the predators are continuously reproducing and maximise fitness by maximising the per capita growth rate. The impact of the predator's presence on consumer behaviour, and the effects of type I and II functional responses on the behaviour of both species are considered. In the analyses, consumers were allowed to co‐ordinate activity or behave independently in relation to other consumers. The ESS‐analysis of the game ensures that no mutant can invade the system. The independent activity was found to be optimal in all analyses, while the co‐ordinated activity was only optimal at full activity where the two activity strategies coincided. The model showed that consumers should change activity to account for predation risk. Activity generally decreased with predation risk. Concerning the energetic aspects, both activity and search speed were important to account for the reproductive output. The functional responses influenced the optimum activity and search speed of consumers and predators. In general, the optimum behaviours showed complex non‐linear responses in relation to the resource and the consumer density. A predator type II functional response had profound impacts on the properties of the optima, the stability and presence of alternative strategies. As a result of the optimum behaviours, the realised functional responses of both species became sigmoidal.
Long‐term experimental evolution in Escherichia coli. V. Effects of recombination with immigrant genotypes on the rate of bacterial evolution
Authors: Souza V. , Turner P. E. , Lenski R. E.
Published: December 2004

This study builds upon an earlier experiment that examined the dynamics of mean fitness in evolving populations of Escherichia coli in which mutations were the sole source of genetic variation. During thousands of generations in a constant environment, the rate of improvement in mean fitness of these asexual populations slowed considerably from an initially rapid pace. In this study, we sought to determine whether sexual recombination with novel genotypes would reaccelerate the rate of adaption in these populations. To that end, treatment populations were propagated for an additional 1000 generations in the same environment as their ancestors, but they were periodically allowed to mate with an immigrant pool of genetically distinct Hfr (high frequency recombination) donors. These donors could transfer genes to the resident populations by conjugation, but the donors themselves could not grow in the experimental environment. Control populations were propagated under identical conditions, but in the absence of sexual recombination with the donors. All twelve control populations retained the ancestral alleles at every locus that was scored. In contrast, the sexual recombination treatment yielded dramatic increases in genetic variation. Thus, there was a profound effect of recombination on the rate of genetic change. However, the increased genetic variation in the treatment populations had no significant effect on the rate of adaptive evolution, as measured by changes in mean fitness relative to a common competitor. We then considered three hypotheses that might reconcile these two outcomes: recombination pressure, hitchhiking of recombinant genotypes in association with beneficial mutations, and complex selection dynamics whereby certain genotypes may have a selective advantage only within a particular milieu of competitors. The estimated recombination rate was too low to explain the observed rate of genetic change, either alone or in combination with hitchhiking effects. However, we documented comple x ecological interactions among some recombinant genotypes, suggesting that our method for estimating fitness relative to a common competitor might have underestimated the rate of adaptive evolution in the treatment populations.
Effects of temperature extremes on genetic variances for life history traits in Drosophila melanogaster as determined from parent‐offspring comparisons
Authors: Sgrò and C. M. , Hoffmann A. A.
Published: December 2004

Parent‐offspring comparisons were used to investigate the effects of temperature extremes on genetic variances for two life history traits and one morphological trait in Drosophila melanogaster. We considered three temperatures (14 °C, 25 °C and 28 °C) for culturing and testing flies, and considered heritabilities, coefficients of additive variation (CVA) and evolvabilities (IA) for fecundity, development time and wing length. For fecundity, heritabilities and evolvabilities were higher when parents were exposed to 14 °C compared to 28 °C. Parent‐offspring comparisons suggested that genetic correlations among environments were close to 1, although lower correlations were obtained in comparisons of family means. Parent‐offspring correlations across environments seemed to depend on parental temperature. For development time, heritabilities and evolvabilities were low at 14 °C compared to 28 °C. However, parent‐offspring correlations were relatively high when the progeny of parents tested at 14 °C were raised at the opposite extreme, suggesting that genetic variation can be enhanced when parents and offspring experience different conditions. CVAs and IAs for development time were lower than for fecundity, even when heritability estimates were similar in magnitude. Genetic variation for wing length was generally not affected by the temperature extremes, and genetic correlations across the extremes estimated from the parent‐offspring comparison were close to 1. There was no evidence for tradeoffs between traits; rapid development time was associated with high fecundity at both the phenotypic and genetic levels. The findings highlight inherent difficulties of estimating genetic parameters from parent‐offspring comparisons when two generations experience different environmental extremes and also show how parent‐offspring comparisons can lead to unexpected findings about the expression of genetic variation.
Seasonality of births in Homo sapiens in pre‐industrial Finland: maximisation of offspring survivorship?
Authors: Lummaa V. , Lemmetyinen R. , Haukioja E. , Pikkola M.
Published: December 2004

We examined the seasonal variation in human birth and infant survival rates in pre‐modern Finland. If survival probabilities of children born during different seasons of the year differ and if timing of reproduction has been affected by natural selection, periodic variation in environment could have led to reproduction during the season of best infant survival expectations. Significant seasonal variation in both birth rate and survival probability was found, but the monthly birth and survival rates of newborn were uncorrelated. Hence, if there was any tendency to maximise the reproductive success, increase in some other component of fitness than the infant survival was probably targeted. The effect of major holidays on the birth rate was proved to be notable, suggesting that although the basis for seasonal variation in birth rate was biological, sociocultural factors had an impact on the timing of reproduction in humans. The overall mortality of infant boys exceeded that of infant girls in all seasons. This difference was smallest during the time of best food supplies, indicating that the development of males was less buffered against environmental disturbances than that of females.
Tracing the colonization of Madeira and the Canary Islands by Drosophila subobscura through the study of the rp49 gene region
Authors: Khadem M. , Rozas J. , Segarra C. , Brehm A. , Aguadé M.
Published: December 2004

Nucleotide variation at the nuclear ribosomal protein 49 (rp49) gene region has been analysed by fine restriction mapping in a sample of 47 lines from a population from Madeira. Five restriction‐site (out of 37 sites scored) and 3 length polymorphisms have been detected, resulting in 14 different haplotypes. This population shows less variation than both continental and Canary Island populations. The population from Madeira shows some differentiation from mainland populations, which does not favor the idea of extensive migration between the continent and Madeira. Chromosomal and restriction‐map variation of the rp49 region in D. subobscura populations, together with data on sequence comparison of this nuclear region in D. guanche and D. madeirensis clearly indicate that the Canary Islands underwent at least two colonization events from the nearby continent. Although the data for Madeira are compatible with a single colonization event by a continental sample polymorphic for gene arrangements O3 and O3 + 4, an alternative scenario with at least two colonization events seems more likely.
Geographic structure of lineage associations in a plant‐bacterial mutualism
Authors: Parker M. A. , Spoerke J. M.
Published: December 2004

Two species linked by a mutualistic relationship may evolve correlated population differentiation if there is long‐term continuity of interactions between specific partners. This phenomenon was analyzed by multilocus enzyme electrophoresis on the annual legume Amphicarpaea bracteata and its nitrogen‐fixing bacterial symbionts (Bradyrhizobium sp.) sampled from >20 sites over a 1000 km area. Three analyses indicated that genetic differentiation was correlated in the two organisms. First, the genetic distance between bacterial populations at each pair of sites was significantly positively related to the genetic distance between their host plant populations, as evaluated by the Mantel test. Second, a cluster analysis revealed that several divergent lineages were present both among plants and among bacteria. Bacterial lineages showed a highly nonrandom distribution across plant lineages that was consistent in each of two regions sampled. Finally, there were numerous cases where populations of the same plant lineage 1000 km apart harbored bacterial isolates with an identical multilocus genotype. Thus, despite recurrent opportunities for partner switching, particular genotypes of these two organisms associate consistently across multiple habitats throughout their geographic range.
The evolution of diet breadth: Monophagy and polyphagy in swallowtail butterflies
Authors: Thompson J. N.
Published: December 2004

Much of the world's biodiversity has resulted from specialization of insect populations onto different plant species, partially through evolution of preference in ovipositing females. Here I report an experimental analysis of how an oviposition preference hierarchy has evolved during the evolutionary diversification of an insect group to produce taxa ranging from monophagous to polyphagous. Tests on the Papilio machaon group of swallowtail butterflies show that the preference hierarchy for plant species is evolutionarily dynamic within this species complex, yet constrained among most populations within species, creating a geographic mosaic of populations differing to various degrees in patterns of host preference. The results indicate that different diet breadths can evolve within a group of closely‐related species through a combination of conservatism in preference hierarchy among some populations, occasional but rare rearrangements in preference among others, correlations in preference for some plant species, and availability of similarly ranked hosts.