Data from: Indirect effects of parasitism: costs of infection to other individuals can be greater than direct costs borne by the host

Parasitic infection has a direct physiological cost to hosts but may also alter how hosts interact with other individuals in their environment. Such indirect effects may alter both host fitness and the fitness of other individuals in their social network, yet the relative impact of direct and indirect effects of infection are rarely quantified. During reproduction, a host's social environment includes family members who may be in conflict over resource allocation. In such situations, infection may alter how resources are allocated, thereby redistributing the costs of parasitism between individuals. Here we experimentally reduce parasite burdens of parent and/or nestling European shags (Phalacrocorax aristotelis) infected with Contracaecum nematodes in a factorial design, then simultaneously measure the impact of an individual's infection on all family members. We found no direct effect of infection on parent or offspring traits but indirect effects were detected in all group members, with both immediate effects (mass change and survival) and longer term effects (timing of parents' subsequent breeding). Our results show that parasite infection can have a major impact on individuals other than the host, suggesting that the effect of parasites on population processes may be greater than previously thought.

寄生虫感染对宿主具有直接生理代价，同时还可改变宿主与环境中其他个体的互动模式。这类间接效应既会改变宿主自身的适合度，也会影响其社会网络内其他个体的适合度，但目前鲜有研究量化感染的直接与间接效应的相对影响强度。在繁殖阶段，宿主所处的社会环境包含可能在资源分配上存在利益冲突的家庭成员。在此类情境中，感染可改变资源分配方式，进而在个体间重新分摊寄生虫感染的代价。本研究采用析因设计，对感染了Contracaecum线虫的欧洲鸬鹚（Phalacrocorax aristotelis）的亲代及/或雏鸟进行寄生虫负荷的实验性下调，同时检测单个个体的感染对所有家庭成员的影响。研究发现，感染并未对亲代或子代的相关性状产生直接效应，但所有群体成员均检测到了间接效应：既包括即时效应（体重变化与存活率），也包括长期效应（亲代后续繁殖的时间节点）。本研究结果表明，寄生虫感染可对宿主以外的其他个体产生显著影响，这提示寄生虫对种群过程的影响可能远超此前的认知。