Long-sperm precedence and other cryptic female choices inDrosophila melanogaster

Abstract

AbstractFemales that mate multiply make postmating choices about which sperm fertilize their eggs (cryptic female choice); however, the male characteristics they use to make such choices remain unclear. In this study, we sought to understand female sperm use patterns by evaluating whetherDrosophila melanogasterfemales adjust sperm use (second male paternity) in response to four main factors: male genotype, male courtship effort, male pheromone alteration, and male postmating reproductive morphology. Our experiment was replicated across four differentD. melanogasterlines, in a full factorial design, including a pheromone manipulation in which second males were perfumed to resemble heterospecific (D. yakuba) males. We found that females prefer longer sperm—regardless of mating order—in almost all contexts; this observed pattern of ‘long-sperm precedence’ is consistent with female postcopulatory choice of high-fitness male traits. Nonetheless, we also found that this general preference can be plastically altered by females in response to effects including perfuming treatment; this differential female sperm use is between otherwise identical males, and therefore solely female-mediated. Furthermore, our finding that females exercise choice using diverse criteria suggests a possible mechanism for the maintenance of variation in sexually selected male traits.Teaser textHow do females make choices about which sperm will fertilize their eggs? In this study, we assess four geographically diverseDrosophila melanogasterlines to show that females strongly prefer long sperm—a pattern consistent with female preference for high-fitness males. In addition, we perfumed males to show that females can adjust this general preference based on other factors, including pheromones. Because this adjustment occurs between genotypically identical males, it is entirely female-mediated.