Publications filtered by: Drosophila
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.
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.
The consequences of sexual interactions extend beyond the simple production of offspring. These interactions typically entail direct effects on female fitness, but may also impact the life histories of later generations. Evaluating the cross-generational effects of sexual interactions provides insights into the dynamics of sexual selection and conflict. Such studies can elucidate whether offspring fitness optima diverge across sexes upon heightened levels of sexual interaction among parents. Here, we found that, in Drosophila melanogaster, components of reproductive success in females, but not males, were contingent on the nature of sexual interactions experienced by their mothers. In particular, maternal sexual interactions with non-sires enhanced female fecundity in the following generation. This highlights the importance of non-sire influences of sexual interactions on the expression of offspring life histories.The consequences of sexual interactions extend beyond the simple production of offspring. These interactions typically entail direct effects on female fitness, but may also impact the life histories of later generations. Evaluating the cross-generational effects of sexual interactions provides insights into the dynamics of sexual selection and conflict. Such studies can elucidate whether offspring fitness optima diverge across sexes upon heightened levels of sexual interaction among parents. Here, we found that, in Drosophila melanogaster, components of reproductive success in females, but not males, were contingent on the nature of sexual interactions experienced by their mothers. In particular, maternal sexual interactions with non-sires enhanced female fecundity in the following generation. This highlights the importance of non-sire influences of sexual interactions on the expression of offspring life histories.
Previous studies indicate that female Drosophila melanogaster are harmed by their mates through copulation. Here, we demonstrate that the harm that males inflict upon females increases with male size. Specifically, both the lifespan and egg-production rate of females decreased significantly as an increasing function of the body size of their mates. Consequently, females mating with larger males had lower lifetime fitness. The detrimental effect of male size on female longevity was not mediated by male effects on female fecundity, egg-production rate or female-remating behaviour. Similarly, the influence of male size on female lifetime fecundity was independent of the male-size effect on female longevity. There was no relationship between female size and female resistance to male harm. Thus, although increasing male body size is known to enhance male mating success, it has a detrimental effect on the direct fitness of their mates. Our results indicate that this harm is a pleiotropic effect of some other selected function and not an adaptation. To the extent that females prefer to mate with larger males, this choice is harmful, a pattern that is consistent with the theory of sexually antagonistic coevolution.
In many species, females exposed to increased sexual activity experience reductions in longevity. Here, in Drosophila melanogaster, we report an additional effect on females brought about by sexual interactions; an effect that spans generations. We subjected females to a sexual treatment consisting of different levels of sexual activity, and then investigated patterns of mortality in their offspring. We found reduced probabilities of survival, increases in the rate-of-senescence, and a pattern of reduced mean longevities, for offspring produced by mothers that experienced higher levels of sexual interaction. We contend that these effects constitute trans-generational costs of sexual conflict – the existence or implications of which have rarely been considered previously. Our results indicate that ongoing exposure by mothers to male pre-copulatory interactions is itself sufficient to drive trans-generational effects on offspring mortality. Thus, we show that increases in maternal sexual activity can produce trans-generational effects that permeate through to latter life-stages in the offspring. This helps to elucidate the complex interplay between sex and ageing, and provides new insights into the dynamics of adaptation under sexual selection.
While model systems are useful in entomology, allowing generalizations to be made based on a few well-known species, they also have drawbacks. It can be difficult to know how far to generalize from information in a few species: are all flies like Drosophila? The use of model systems is particularly problematic in studying sexual selection, where variability among taxa is key to the evolution of different behaviors. A bias toward use of a few insect species, particularly Drosophila, is evident in the sexual selection and sexual conflict literature over the last several decades, although the diversity of study organisms has increased more recently. As the number of model systems used to study sexual conflict increased, support for the idea that sexual interactions resulted in harm to females decreased. Future work should choose model systems thoughtfully, combining well-known species with those that can add to the variation that allows us to make more meaningful generalizations.