Data from: Reproductive effort influences intra-seasonal variation in parasite-specific antibody responses in wild Soay sheep

A trade‐off between reproduction and immune function has been suggested to potentially underpin between‐individual and genetic variation in reproductive strategy, immunity, and lifespan, with potential consequences for host and parasite dynamics. Previous studies in wild animal populations have shown that experimentally‐induced or natural variation in reproductive effort is negatively associated with general immune markers. Few studies, however, have tackled this question by measuring specific immune responses against prevalent pathogens, and only rarely has variation in immune measures been linked to parasite burden, making it impossible to draw conclusions about the functional relevance of covariation between reproductive effort and immune markers. We collected faecal samples in a longitudinal manner from wild female Soay sheep across late pregnancy and early lactation, and measured gastrointestinal nematode faecal egg count (FEC) and worm‐specific antibody responses. FEC was highly repeatable, with ~80% of variation due to between‐individual differences, while three isotypes of worm‐specific and total antibodies had moderate repeatability (range: 11‐43%). Females making a greater reproductive effort (those that reproduced, and especially those with heavier litters), showed a more rapid increase in FEC across the season, while non‐reproducing females and those producing lighter litters experienced lower FEC and had higher antibody levels. Associations between antibodies and FEC were complex: worm‐specific immunoglobulin (Ig) G was negatively associated with FEC, while total IgM was positively associated, emphasizing the importance of measuring both immune markers and parasite burden in ecological studies. Our results support the predicted trade‐off between reproductive effort and parasite‐specific immunity: high reproductive effort can limit the ability of individuals to defend themselves against prevalent parasites, with potential downstream consequences for fitness and parasite transmission.

繁殖与免疫功能之间的权衡假说，被认为可能是繁殖策略、免疫能力与寿命存在个体间及遗传差异的内在机制，并可能对宿主与寄生虫的动态平衡产生影响。此前针对野生动物种群的研究表明，实验诱导或自然存在的繁殖投入变异，与通用免疫标志物呈负相关关系。然而，鲜有研究通过测定宿主针对流行病原体的特异性免疫应答来探讨该问题，且免疫指标变异与寄生虫负荷的关联分析亦极为罕见，这使得学界无法就繁殖投入与免疫标志物之间的协变关系的功能相关性得出可靠结论。本研究以野生雌性索艾羊（Soay sheep）为研究对象，在妊娠晚期至泌乳早期开展纵向粪便样本采集，并测定了胃肠道线虫粪便虫卵计数（FEC）与蠕虫特异性抗体应答水平。粪便虫卵计数具有极高的重复性，约80%的变异源于个体间差异；而三种蠕虫特异性及总抗体的同种型则呈现中等程度的重复性（变异范围11%~43%）。繁殖投入更高的雌性个体（即成功繁殖的个体，尤其是产羔数较多的个体），其粪便虫卵计数在整个观测季内增长更为迅速；而未繁殖个体与产羔数较少的个体，其粪便虫卵计数更低，抗体水平则更高。抗体与粪便虫卵计数之间的关联较为复杂：蠕虫特异性免疫球蛋白G（IgG）与粪便虫卵计数呈负相关，而总免疫球蛋白M（IgM）则呈正相关，这凸显了在生态学研究中同时测定免疫标志物与寄生虫负荷的重要性。本研究结果验证了繁殖投入与寄生虫特异性免疫之间存在权衡的理论预测：高繁殖投入会限制个体对抗流行寄生虫的能力，进而可能对个体适合度与寄生虫传播产生后续影响。