Male moths reduce sperm investment in relatives

Sperm production carries costs and males frequently tailor their ejaculates to maximize their reproductive success. Previous work shows that males are sensitive to variation in female quality, and to the risk and intensity of sperm competition, and adjust their ejaculates accordingly. Males and females of many species are sensitive to the relatedness of their mating partners and may forego mating with related individuals altogether to avoid the costs of inbreeding. In addition, in polyandrous species, females can potentially invoke postcopulatory mechanisms to avoid using related males' sperm, but to date no study has demonstrated that males also discriminate against related females at the level of the gamete. In this study on the Indian meal moth, Plodia interpunctella, males provided unrelated females with more fertile and nonfertile sperm than their sisters. These results indicate that male moths can minimize the potential costs of inbreeding by carefully managing their limited sperm supplies in relation to partner relatedness.