EVOLUTION OF COURTSHIP SONG AND REPRODUCTIVE ISOLATION IN THE DROSOPHILA WILLISTONI SPECIES COMPLEX: DO SEXUAL SIGNALS DIVERGE THE MOST QUICKLY?

Reproductive isolation increases with genetic distance between species. Although sexual selection may drive divergence of sexual signals and traits, causing rapid evolution of sexual isolation, quantitative data supporting this idea are rare. We examine the rates of divergence of a species-specific courtship signal, sexual isolation, and postmating isolation in the Drosophila willistoni group. Both types of isolation increase with genetic distance and postmating isolation is the most strongly correlated with genetic divergence, suggesting this has the least variable divergence rate. Song divergence is not correlated with genetic divergence. Homoplasy in song pattern results in poorly resolved phylogenies that are different from molecular phylogenies. Song evolves more quickly than sexual isolation, which evolves more quickly than postmating isolation.     

Sex and differentiation: population genetic divergence and sexual dimorphism in Mexican goodeid fish

Genetic differentiation arises due to the interaction between natural and sexual selection, migration and genetic drift. A potential role of sexual selection in speciation has received much interest, although comparative studies are inconsistent in finding supporting evidence. A poorly tested prediction is that species subject to a higher intensity of sexual selection should show greater genetic differentiation amongst populations because females from these populations should be more choosy in mate choice. The Goodeinae is a group of endemic Mexican fishes in which female choice has driven some species to be morphologically sexually dimorphic, whereas others are relatively monomorphic. Here, we measured population divergence, using microsatellite loci, within four goodeid species which show contrasting levels of sexual dimorphism. We found higher levels of differentiation between populations of the more dimorphic species, implying less gene flow between populations. We also found evidence of higher levels of genetic differences between the sexes within populations of the dimorphic species, consistent with greater dispersal in males. Adjusted for geographic distance, the mean F(ST) for the dimorphic species is 0.25 compared with 0.16 for the less dimorphic species. We conclude that population differentiation is accelerated in more sexually dimorphic species, and that comparative phylogeography may provide a more powerful approach to detecting processes, such as an influence of sexual selection on differentiation, than broad-scale comparative studies.     

Fisher's sons’ effect in sexual selection: absent,intermittent or just low experimental power?

The Fisherian sexual selection paradigm has been called the null model of sexual selection. At its heart is the expectation of a genetic correlation (r_G) between female preference and male trait. However, recent meta‐analysis has shown estimated correlations are often extremely weak and not statistically significant. We show here that systematic failure of studies to reject the null hypothesis that r_G = 0 is almost certainly due to the low power of most experimental designs used. We provide an easy way to assess experimental power a priori and suggest that current data make it difficult to definitively test a key component of the Fisher effect.     

Genetic independence of female signal form and male receiver design in the almond moth, Cadra cautella

Efficient signalling requires coordination of signal form and receiver design. To maintain signal function, parallel changes in signaller and receiver traits are required. Genetic correlation and co-evolution among signal and response traits have been proposed to preserve signal function (i.e. coordination) during the evolution of mate recognition systems. Empirical studies have provided support for both mechanisms; however, there is debate regarding the interpretation of some of these studies. Tests for a genetic correlation typically hybridize divergent signalling systems and look at hybrid signal form and receiver design, or impose artificial selection on signal form and look for an indirect response to selection in receiver design. Some of the hybridization studies did not achieve reassortment of genes from the parental types, whereas some of the artificial selection studies incorporated random mating in their designs. As a result of these limitations, the hybridization studies cannot discriminate between genetic correlation and co-evolution with primarily additive genetic effects underlying signal and response traits. Similarly, the artificial selection experiments cannot discriminate between genetic correlation because of linkage disequilibrium and co-evolution. This study examined the mating preferences of male almond moths, Cadra cautella, before and after female moths were artificially selected (using a design incorporating assortative mating) for novel pheromone blend ratios. Our results demonstrate the absence of a genetic correlation between signal and response traits in the almond moth.     

ON THE EVOLUTIONARY CONSEQUENCES OF SEXUAL IMPRINTING

The idea that sexual imprinting may generate sexual selection and possibly lead to speciation has been much discussed in the ethological literature. Here the feasibility of three such hypotheses is investigated using mathematical models of sexual selection in which mating preferences are acquired through imprinting and hence dependent upon the parental phenotypes. The principal findings are the following. (1) Sexual imprinting reduces the likelihood of novel adaptive traits spreading through a population, except in some circumstances in which there is heterozygote advantage. (2) Asymmetrical mating preferences, acquired through imprinting, can generate sexual selection for traits that impair survival. (3) The conditions under which sexual imprinting will maintain a genetic polymorphism in a population are fairly restricted. (4) Sexual imprinting can act as a barrier to gene flow minimizing the impact of migration and preserving and accentuating genetic differences between populations. The findings suggest that sexual imprinting may be of considerable evolutionary significance.     

QTL for the species-specific male and female genital morphologies in Ohomopterus ground beetles

Animals with internal fertilization often exhibit marked diversification in genital morphology among closely related species. However, our knowledge of the genetic architecture underlying genital evolution is still limited. We constructed genetic linkage maps and analysed quantitative trait loci (QTL) for F₂ hybrids of two closely related species of the carabid beetles Carabus (Ohomopterus) iwawakianus and C. (O.) maiyasanus, which show matching male and female genital shapes within species, but marked differences in genital morphologies between species. The linkage maps comprised both amplified fragment length polymorphism and microsatellite markers. Composite interval mapping to detect QTL for three traits of male copulatory piece (length, width, weight) and two traits for female vaginal appendix (length, width) resulted in the detection of one to five significant QTL for each trait. The QTL explained large proportions of phenotypic variance. Thus, the interspecific difference in the genital morphologies appeared to be determined by relatively small numbers of genes with large genetic effects. QTL of different traits for the same or different sexes co‐occurred on five of eight linkage groups with significant QTL; in particular, three QTL for different male and female genital traits occurred almost at the same position. Each of the male genital traits showed uniform signs of additive genetic effects, suggesting that directional selection has led to species‐specific morphologies. However, the signs of additive genetic effects in each female genital trait were not uniform, suggesting that coevolution between sexes is not necessarily concerted. This result requires further assessment because the sample size of F₂ females was small.     

昆虫求偶鸣曲的行为特征与功能及其生态学意义

以直翅目昆虫为重点,从鸣曲器官的结构特征与鸣曲机理,求偶鸣曲的定位及其精度,求偶鸣曲的适度调节,求偶鸣曲的结构参数及其生物学意义,受体对求偶鸣曲的反应与识别五个方面对昆虫求偶鸣曲的行为特征与功能作了综述。在此基础上,从求偶鸣曲的遗传与进化,求偶鸣曲与自然选择和性选择,求偶鸣曲与物种的分化和进化三个角度探讨了求偶鸣曲的生态学意义,并展望了该领域未来的发展趋势和研究方向。