Experimental population demography reveals sex specific density dependence as an outcome of sexual conflict

Abstract

Many demographic models assume that only females matter for population dynamics. However, theory and evidence of sexual conflict suggest that males can affect female fitness through mating competition between and within the sexes, yet it is unclear how such effects may influence population dynamics. We used experimental population demography to understand how sexual conflict affects offspring recruitment in Drosophila melanogaster, a model species for studying the evolution of sexual conflict. By manipulating sex ratio and male/female density independently in a response surface design we found that increasing male density, and thereby the intensity of sexual conflict, led to fewer offspring per female, but that effect was nearly half the strength of female density dependence. Consistent with this, our best fitting birth function showed female dominance of births with sex-specific density dependence, indicating that males have a demographic effect even if females have demographic dominance. Our results confirm that females have a larger influence than males on offspring recruitment, however, more importantly our result increases our understanding about the demographic effects males have through sexual conflict.