Abstract
Female promiscuity can generate postcopulatory competition among males, but it also provides the opportunity for exploitation of rival male ejaculates. For example, in many insect species, male seminal fluid proteins (Sfps) transferred in a female's first mating stimulate increased fecundity and decreased receptivity to remating. Subsequent mates of females could potentially take advantage of the effects of the first male's Sfps and strategically reduce investment in their own ejaculate. We compared postmating responses (fecundity and sexual receptivity) of Drosophila melanogaster females after their first (virgin) matings (V), to the responses of females remating (M) 24 h after their first mating. The results show that M matings fail to boost fecundity and, thus, males are unlikely to gain fitness from transferring Sfps whose sole function-in V matings-is fecundity-stimulation. However, males can protect their likelihood of paternity in M matings through the transfer of receptivity-inhibiting Sfps. The levels of a fecundity-stimulating Sfp (ovulin) were significantly lower in M females relative to V females, at the same time point shortly after the end of mating. In contrast, the levels of a key receptivity-inhibiting Sfp (sex peptide) were the same in M and V females. These results support the hypothesis that males can adaptively tailor the composition of proteins in the ejaculate, allowing a male to take advantage of the fecundity-stimulating effects of the previous male's ovulin, yet maintaining investment in sex peptide. Furthermore, our results demonstrate sophisticated protein-specific ejaculate manipulation.
