Ecological Implications of Sex Ratio Variation in Mosquitofish

Divergence between the sexes is one of the most overt forms of genetic and phenotypic variation within populations of many species. This variation has a history of evolutionary investigation but sexual dimorphism may also be important from an ecological perspective. Indeed where the two sexes of a species have different ecological roles, changes in sex ratios due to differential patterns of ecological selection may in turn lead to different ecological feedbacks on population, community, or ecosystem dynamics. We examined the potential for such eco-evolutionary dynamics in the sexually dimorphic eastern mosquitofish (Gambusia holbrooki).  These fish are dimorphic in overt traits, such as size and morphology, as well as less overt traits, such as behavior.  Here we provide evidence that ecological conditions tied to predator regimes lead to biased sex ratios of mosquitofish, due to a combination of large females experiencing increased predation and males experiencing shortened lifespans from reproductive effort.  We provide results from mesocosm experiments that isolate potential community and ecosystem effects of sex ratio variation from effects associated with fish density and predation.  As such, this work represents an initial step in incorporating sexual dimorphism into an eco-evolutionary dynamics framework that has largely overlooked sexually selected traits.