Sexual cannibalism benefits offspring survival

Polyandry may provide females with benefits that directly affect their condition and fecundity and/or that enhance the quality of their offspring through receiving better or more compatible paternal genes. In polyandrous species with sexual cannibalism, females may gain considerable nutritional benefits through consuming a mating partner. However, in many spiders with high rates of sexual cannibalism, males are very small compared to the females and nutritional gains through sexual cannibalism are considered small or absent. While this is widely accepted, no study has tested for effects of multiple mating with and without sexual cannibalism on female and offspring fitness. We designed an experiment that simultaneously investigated direct and indirect benefits of polyandry and sexual cannibalism in the orb-web spider Argiope bruennichi. We used monandrous and polyandrous females that were either allowed to consume their mating partner or not and recorded fecundity traits and offspring survival under simulated overwintering conditions. We found that female mating rate did not affect fecundity or offspring survival. But independent of female mating rate and the number of males consumed, cannibalistic females produced bigger clutches with heavier eggs. Cannibalistic females produced offspring with a prolonged survival time compared to the offspring of females that were prevented from eating males. This prolonged offspring survival was independent of female mating rate and the number of males consumed.