A polyandrous female moth discriminates against previous mates to gain genetic diversity

Abstract

Polyandry is common in many animal species. The hypotheses proposed to explain the evolution of polyandry generally fall into two categories: to gain material benefits and to obtain genetic benefits. Here we report our findings on a polyandrous moth, Ephestia kuehniella (Lepidoptera: Pyralidae). The present study does not support the hypothesis that females gain material benefits from multiple copulations in terms of sperm replenishment, fecundity and longevity, because females that copulated once and females that copulated more than once with the same or different males had similar fertility, fecundity and longevity. Females used three strategies to gain possible genetic benefits: discriminating against previous mates probably via chemical cues, giving 60% chance of paternity to second males, and adjusting their oviposition patterns depending on whether they encountered new or previous mates after the first copulation. For the third strategy, females that encountered new mates after the first copulation saved eggs until the next day to facilitate fertilization of their eggs with the sperm of their new mates. Our findings do not support the hypothesis that polyandry increases offspring viability, because polyandry did not affect egg hatching success, offspring survival or weight. Ephestia kuehniella showed limited ability to disperse, and females laid all their eggs locally, mostly within 2 days, suggesting that offspring live together and that sib copulations are common in this species. Therefore, polyandry is probably a mechanism for reducing sib competition and inbreeding costs in offspring.