Abstracts (first author)
Female age dependent responses to a male signal can alter opportunities for sexual antagonistic co-evolution
Evolutionary explanations for ageing are based on the observation that the strength of selection often wanes with age. While this is well established for natural selection, data on the age-specific expression and benefits of sexually selected traits are lacking. Here we present work to address this omission. We report the responses of Drosophila melanogaster females of different ages to receipt of an ejaculate protein, the sex-peptide (SP) transferred to females during mating. SP can mediate sexual conflict as it can cause fitness costs in females, while simultaneously benefitting the males that transfer it. Virgin and mated females of all ages showed significantly reduced receptivity to further mating in response to SP. However increases in egg laying in response to receipt of SP were observed only in young virgin females. Hence there was a narrow demographic window in which males could maximise the fitness benefits gained by transfer of SP. The pattern of female responses to SP reversed with increasing female age, hence altering the opportunity for selection. The data reveal a new example of demographic variation in the strength of selection, with convergence and conflicts of interest between males and ageing females occurring over different facets of responses to a sexually antagonistic trait.