Sexual conflict and cooperation in butterfly reproduction: a comparative study of polyandry and female fitness

Most butterfly species can be characterized as capital breeders, meaning th at reproductive output is strongly coupled to the amount of resources they have procured during the larval stage. Accordingly, female fecundity is gen erally correlated with female mass, both within and across species. However , the females of some species can be partly characterized as income breeder s. in the sense that their reproductive output is dependent not only on lar val-derived capital but also on resources acquired during the adult stage. These adult resources can be derived from female feeding or from male-trans ferred nuptial gifts. Recent studies on the within-species effects of multi ple matings on female fitness show that females generally gain directly fro m multiple matings in terms of increased lifetime offspring production. Her e, we test whether the positive effects of multiple mating on female fitnes s also hold at a comparative level, by conducting a laboratory study of fem ale reproductive output in eight pierid species that differ in lifetime fem ale mating frequency. Female reproductive output, measured as cumulative eg g mass divided by female mass, increased significantly with polyandry (r = 0.942, p < 0.001), demonstrating that the positive effect of mating rate on female reproductive fitness also holds between species. The positive effec t of male nutrient contribution is substantial, and the per capita reproduc tive output is more than twice as high in the most polyandrous species as i n the most monandrous ones. Hence, the positive net effect of the ejaculate s is highly substantial, although males and females can have sexual interes ts that run counter to each other, setting the stage for sexually antagonis tic coevolution, so that the various component parts of the male ejaculate- sperm, nutrients, anti-aphrodisiacs, and gonadotrophic hormones-may each co rrespond to a separate conflict-cooperation balance between the sexes. Two scenarios for the evolution of nuptial gifts in butterflies are discussed, one arguing that variation in larval food is the underlying factor and the other arguing that sexually antagonistic coevolution is the driving force. The two views are complementary rather than mutually exclusive, although th e former hypothesis predicts that variation in female mating rate depends o n variation in larval food availability, whereas the latter suggests that v ariation in female mating rate between species results from species-specifi c idiosyncrasies.