Publications filtered by: Sexual selection
It is well known that sexual selection can target reproductive traits during successive pre- and post-mating episodes of selection. A key focus of recent studies has been to understand and quantify how these episodes of sexual selection interact to determine overall variance in reproductive success. In this paper we review empirical developments in this field but also highlight the considerable variability in patterns of pre- and post-mating sexual selection, attributable to variation in patterns of resource acquisition and allocation, ecological and social factors, genotype-by-environment interaction, and possible methodological factors that might obscure such patterns. Our aim is to highlight how (co)variances in pre- and post-mating sexually selected traits can be sensitive to changes in a range of ecological and environmental variables. We argue that failure to capture this variation when quantifying the opportunity for sexual selection may lead to erroneous conclusions about the strength, direction or form of sexual selection operating on pre- and post-mating traits. Overall, we advocate for approaches that combine measures of pre- and post-mating selection across contrasting environmental or ecological gradients to better understand the dynamics of sexual selection in polyandrous species. We also discuss some directions for future research in this area.
Recognition of the ubiquity of female multiple mating has evoked an important shift in sexual selection research, emphasising the adaptive nature of female mating strategies. While phenotypic changes in female mating traits have been previously studied, little is known about the genetic basis of female mating behaviour and its potential to respond to selection at different stages throughout an individual’s life. Using a large quantitative genetic breeding design, we observed lifetime female mating behaviour in Drosophila melanogaster to examine the effect of female age and mating history on three key mating traits: courtship latency, mating latency and copula duration. Courtship latency (time until males initiate courtship) decreased with the cumulative number of females’ previous matings. Mating latency (defined here as the time between the beginning of courtship and the start of copulation) increased with female age, and copula duration was found to decrease as females aged. We calculated quantitative genetic estimates for mating traits in virgin females and at the females’ third mating to examine changes in the evolutionary potential of mating traits. We found considerable additive genetic variation in courtship latency and mating latency measured in virgin females. Copula duration displayed no heritable variation among females across sire families, but male effects were consistent with the idea that this trait is under male control. Heritability estimates differed significantly from zero in virgin females for courtship latency and mating latency. Heritability estimates did not differ significantly from zero when females were mating for the third time. However, overlapping 84% confidence intervals between heritability estimates obtained from virgin and mated females suggest that female mating strategies may have the potential to respond to selection at these different life stages.
Polyandry is widespread despite its costs. The sexually selected sperm hypotheses (‘sexy’ and ‘good’ sperm) posit that sperm competition plays a role in the evolution of polyandry. Two poorly studied assumptions of these hypotheses are the presence of additive genetic variance in polyandry and sperm competitiveness. Using a quantitative genetic breeding design in a natural population of Drosophila melanogaster, we first established the potential for polyandry to respond to selection. We then investigated whether polyandry can evolve through sexually selected sperm processes. We measured lifetime polyandry and offensive sperm competitiveness (P2) while controlling for sampling variance due to male x male x female interactions. We also measured additive genetic variance in egg-to-adult viability and controlled for its effect on P2 estimates. Female lifetime polyandry showed significant and substantial additive genetic variance and evolvability. In contrast, we found little genetic variance or evolvability in P2 or egg-to-adult viability. Additive genetic variance in polyandry highlights its potential to respond to selection. However, the low levels of genetic variance in sperm competitiveness suggest the evolution of polyandry may not be driven by sexy sperm or good sperm processes.
Females that mate with multiple males (polyandry) may reduce the risk that their eggs are fertilized by a single unsuitable male. About 25 years ago it was hypothesized that bet-hedging could function as a mechanism favoring the evolution of polyandry, but this idea is controversial because theory indicates that bet-hedging via polyandry can compensate the costs of mating only in small populations. Nevertheless, populations are often spatially structured, and even in the absence of spatial structure, mate choice opportunity can be limited to a few potential partners. We examined the effectiveness of bet-hedging in such situations with simulations carried out under two scenarios; (1) intrinsic male quality, with offspring survival determined by male phenotype (male’s ability to generate viable offspring), and (2) genetic incompatibility (offspring fitness determined non-additively by parental genotypes). We find higher fixation probabilities for a polyandrous strategy compared to a monandrous strategy if complete reproductive failure due to male effects or parental incompatibility is pervasive in the population. Our results also indicate that bet-hedging polyandry can delay the extinction of small demes. Our results underscore the potential for bet-hedging to provide benefits to polyandrous females and have valuable implications for conservation biology.
The trade-off between survival and reproduction is fundamental to life history theory. Sexual selection is expected to favour a live fast die young life history pattern in males due to increased risk of extrinsic mortality associated with obtaining mates. Sexual conflict may also drive a genetic trade-off between reproduction and lifespan in females. We found significant additive genetic variance in longevity independent of lifetime mating frequency, and in early life mating frequency. There was significant negative genetic covariance between these traits indicating that females from families characterized by high levels of multiple mating early in life die sooner than females that engage in less intense early life mating. Thus, despite heritable variation in both traits, their independent evolution is constrained by an evolutionary trade-off. Our findings indicate that, in addition to the well-known male-driven direct costs of mating on female lifespan (mediated by male harassment and the harmful effects of male seminal fluids), females with a genetic propensity to mate multiply live shorter lives. We discuss the potential role of sexual conflict in driving the evolutionary trade-off between reproduction and lifespan in Drosophila. More generally, our data show that, like males, females can exhibit a live fast die young life history strategy.