Parental relatedness and parasitoid sex ratios under local mate competition

Abstract

Sex ratio theory predicts that, under local mate competition, a more female‐biased offspring sex ratio will be produced by females when their relatedness to their mates is closer. We assess how the sexual composition of broods responds to mother–mate relatedness using Goniozus legneri Gordh (Hymenoptera: Bethylidae), a parasitoid wasp that has biased sex ratios due to local mate competition. Relatedness was varied by providing virgin females with a mate that was either a sibling, a non‐sibling from the same strain, from a strain with geographically similar origin or from a strain with geographically distant origin. The sex ratios among broods produced by mothers that had mated with a sibling or a same‐strain male were similar and were more biased than broods produced by females mated with males from a different strain. Brood sex variances were higher after mating with different‐strain males. Previous evaluations of parasitoid sex ratio responses to mate relatedness have not found the patterns predicted, possibly because the species investigated can control progeny sex ratio but cannot discriminate kin. In contrast, female G. legneri appear to possess both these abilities and appears to respond to mate relatedness in qualitative agreement with theoretical predictions