Evolution of male costs of copulation in sepsid flies (Diptera: Sepsidae)

Reproduction is well known to be costly for females, but longevity costs of copulations in males are still poorly understood. In particular, the effect of the number of copulations on male longevity is rarely considered. Work on black scavenger flies (Diptera: Sepsidae) showed contrasting results: in Saltella sphondylii the number of copulations is strongly negatively correlated with male longevity, whereas in Sepsis cynipsea mated males did not suffer from reduced longevity. Here we summarize the findings of several studies covering four additional species of sepsid flies from across the phylogenetic tree of sepsids to better understand the evolution of male reproductive costs in this clade. After accounting for the mating system differences between species, we find no evidence for longevity costs in Allosepsis sp., Sepsis fulgens and Themira superba , while in Saltella nigripes multiple copulations drastically reduced longevity. Mapping this trait onto the most current phylogenetic hypothesis for Sepsidae suggests that male cost in Saltella is derived while there is an absence of longevity costs for all other sepsids. We discuss the origin of this novel longevity cost in Saltella in the context of a change in their reproductive strategy, namely the evolution of high polygynandry coupled with unusually brief copulations.