Asymmetries affecting aggressive contests between solitary parasitoids: the effect of host species

Conflicts in animals are usually resolved based on asymmetries, where contest winners are often those that value a resource the most and/or those who have the greatest potential to retain it. In parasitoid wasps, contests between females determine which individual exploits hosts for offspring production. Previous studies on solitary parasitoids rarely considered the role of biotic factors generating phenotypic variation that could influence the strength of asymmetries. Some parasitoid species parasitize host species of various sizes, producing offspring that vary considerably in size and potentially fighting ability. In this study, we reared the egg endoparasitoid Telenomus podisi (Hymenoptera: Scelionidae) on two host species to measure the effect of body size on contest resolution and how it interacts with ownership and resource value asymmetries. Our results showed that ownership status best predicts final contest outcome when similar sized wasps fight over hosts. The frequency and outcomes of individual fights structuring contests were better explained by the difference in the number of eggs laid in the hosts by each female at a given time. When contestants varied in body size, larger intruders frequently dislodged small owners regardless of ownership and resource value asymmetries. These results imply that body size is an important factor to consider in solitary parasitoid contests and that it can overshadow the effects of other asymmetries. Our study suggests that host community diversity could have a direct effect on parasitoid contests and that biotic communities, through their effects on animal phenotypes, may play an underrated role in contest resolution.

动物间的冲突通常依托不对称性得以解决，冲突的获胜者往往是对某一资源估值最高的个体，或是最具保有该资源能力的个体。在寄生蜂（parasitoid wasps）中，雌性个体间的争斗决定了哪只个体可利用寄主进行后代繁育。此前针对独居寄生蜂（solitary parasitoids）的研究，极少关注可产生表型变异的生物因子对不对称性强度的影响作用。部分寄生蜂物种可寄生不同体型的寄主，其后代体型差异显著，争斗能力也可能随之发生变化。本研究以两种寄主繁育卵内寄生蜂（egg endoparasitoid）豆荚蝽黑卵蜂（Telenomus podisi，膜翅目：黑卵蜂科），旨在探究体型大小对争斗结局的影响，以及体型如何与所有权、资源价值不对称性产生交互作用。研究结果显示，当体型相近的蜂类争夺寄主时，所有权状态最能预测最终的争斗结果。构成整场争斗的单次打斗的频率与结局，更可通过“特定时间内每只雌性在寄主上的产卵数量差异”得到解释。当争斗双方体型存在差异时，体型更大的入侵者往往会驱逐体型较小的寄主占有者，且不受所有权与资源价值不对称性的影响。上述结果表明，体型是独居寄生蜂争斗中需重点考量的关键因素，其影响甚至可掩盖其他不对称性的作用。本研究提示，寄主群落多样性可能直接影响寄生蜂的争斗行为；而生物群落通过调控动物表型，可能在冲突解决中发挥了此前被低估的重要作用。