Sexual conflict over mating duration in Drosophila melanogaster

Mating duration varies widely between and within species, often lasting longer than is necessary for sperm transfer. Prolonged copulations can be energetically expensive and take time and resources that could otherwise be directed elsewhere, so extended matings likely provide benefits to one or both sexes that outweigh these costs. In the fruit fly, Drosophila melanogaster, mating duration is primarily under male control and continues after sperm transfer has ended. Although there is evidence that mating duration may affect fitness-related traits in this system, controlled experiments investigating the impacts of naturally occurring variation in mating duration on both males and females are lacking. We used hemiclonal analysis in D. melanogaster to investigate the consequences of prolonged matings for both sexes by mating males from long- and short-mating hemiclone lines to females of varying sizes. Males with longer mating durations sired a greater proportion of offspring (i.e. had higher defensive reproductive success) with small females than males with shorter mating durations, indicating that males benefited from prolonged matings. In contrast, longer matings were harmful to females, as both large and small females had significantly lower fecundity after mating with males from long-mating hemiclone lines compared to males from short-mating hemiclone lines. Our findings demonstrate that mating duration is involved in sexual conflict in D. melanogaster, providing insight into the mechanisms maintaining variation in mating duration within species.