Data from: Differential host responses to parasitism shape divergent fitness costs of infection

Fitness costs of infection are fundamental to understanding the ecology and evolution of host-parasite interactions. However, these costs, and particularly their underlying mechanisms, are challenging to evaluate in wild populations. Here, we quantified total and species-specific costs of gastrointestinal worms on African buffalo, by combining the power of an anthelmintic treatment experiment that perturbed the entire worm community with a longitudinal study that tracked the two most dominant community members. Reducing all worms improved buffalo body condition, which was strongly associated with increases in survival and reproduction. Species-specific analyses revealed that condition-mediated fitness costs of infection differed between parasite species. Hosts that gained the blood-sucking worm Haemonchus, lost condition, and this loss may have been mediated by reductions in forage intake. Hosts that resisted Haemonchus by elevating IL-4 and eosinophil immune defences were able to reduce their parasite loads and gain back condition. Conversely, hosts that gained Cooperia, a less pathogenic worm, gained condition and had higher survival and reproductive success. Elevating immune defences had no effect on Cooperia abundance. Coupled with the positive relationship observed between Cooperia and host condition, our data suggest that hosts might benefit from tolerating Cooperia rather than incurring the costs of resistance. Overall, our study reveals that differential host responses to parasites play a key role in mediating the costs of infection.

感染的适合度代价是理解宿主-寄生虫相互作用的生态学与进化的基础。然而，这类代价，尤其是其背后的作用机制，在野生种群中难以量化评估。本研究结合可扰动整个线虫群落的驱虫治疗实验，与追踪两种最优势线虫类群的纵向研究，量化了胃肠道线虫对非洲水牛的总适合度代价及物种特异性代价。清除全部胃肠道线虫可改善非洲水牛的体况，这一改善与存活率和繁殖率的显著提升密切相关。物种特异性分析结果显示，由体况介导的感染适合度代价因寄生虫物种而异。感染吸血线虫血矛线虫（Haemonchus）的水牛个体体况下降，这一体况损失可能由采食量减少所介导。通过上调IL-4和嗜酸性粒细胞免疫防御来抵抗血矛线虫的宿主，能够降低自身的寄生虫负荷并恢复体况。与之相反，感染古柏线虫（Cooperia）——一种致病性较低的线虫——的水牛个体则体况提升，并获得更高的存活率与繁殖成功率。上调免疫防御对古柏线虫的种群丰度无显著影响。结合古柏线虫与宿主体况间的正相关关系，本研究数据表明，宿主或许更适合耐受古柏线虫，而非付出免疫抵抗的代价。总体而言，本研究揭示，宿主对寄生虫的差异化应答在介导感染代价的过程中发挥关键作用。