A sex allocation cost to polyandry in a parasitoid wasp

The costs and benefits of polyandry are central to understanding the near-ubiquity of female multiple mating. Here, we present evidence of a novel cost of polyandry: disrupted sex allocation. In Nasonia vitripennis, a species that is monandrous in the wild but engages in polyandry under laboratory culture conditions, sexual harassment during oviposition results in increased production of sons under conditions that favour female-biased sex ratios. In addition, females more likely to re-mate under harassment produce the least female-biased sex ratios, and these females are unable to mitigate this cost by increasing offspring production. Our results therefore argue that polyandry does not serve to mitigate the costs of harassment (convenience polyandry) in Nasonia. Furthermore, because males benefit from female-biased offspring sex ratios, harassment of ovipositing females also creates a novel cost of that harassment for males.

一妻多夫制（polyandry）的成本与收益，是解析雌性多次交配现象近乎普遍存在的核心议题。本研究首次揭示了一妻多夫制的一类全新成本：性别分配紊乱。本研究以野外表现为单配偶制、但在实验室培养条件下可发生一妻多夫行为的丽蝇蛹集金小蜂（Nasonia vitripennis）为研究对象，发现在偏雌性性别比例适宜的条件下，产卵过程中的性骚扰会导致雄性子代产出量增加。此外，在骚扰压力下更易发生再次交配的雌性个体，其后代性别比例的偏雌性程度最低，且这类雌性无法通过提升子代总繁殖量来抵消该成本。因此本研究结果表明，在丽蝇蛹集金小蜂中，一妻多夫制并不能缓解性骚扰带来的成本——这也意味着“便利型一妻多夫制（convenience polyandry）”假说在此物种中不成立。此外，由于雄性可从偏雌性的后代性别比例中获益，对产卵雌性的性骚扰同时也为雄性自身带来了一种全新的骚扰相关成本。