Social living simultaneously increases infection risk and decreases the cost of infection

Elevated parasite infection risk is considered to be a near universal cost of social living. However, living in groups may also provide benefits that reduce the negative impacts of infection. These potential ‘tolerance’ benefits of living socially are theoretically possible, but have rarely been described. In this study, we used an anthelmintic treatment experiment in wild Grant’s gazelles (Nanger granti), who are commonly infected with gastrointestinal nematodes (GIN), to show that social living confers both costs and benefits related to GIN parasitism. We show that although larger group size increases GIN infection risk, a key cost of GIN infection – the suppression of food intake − is simultaneously moderated by living in larger groups. Our findings help illuminate the complex role parasites play in the evolution of host social behavior.寄生虫感染风险升高，被普遍视为群居生活几乎共通的代价。然而，群居生活也可能带来益处，缓解感染所造成的负面影响。这种通过群居生活实现的潜在‘耐受’益处仅在理论层面具备可行性，却鲜有相关实证报道。本研究针对普遍感染胃肠道线虫（gastrointestinal nematodes, GIN）的野生葛氏瞪羚（Nanger granti）开展驱虫处理实验，以此证明群居生活同时存在与胃肠道线虫寄生相关的代价与益处。研究结果显示，尽管种群规模扩大会提升胃肠道线虫的感染风险，但群居规模扩大同时会缓解感染带来的核心代价——食物摄入受抑制的情况。本研究结果有助于阐明寄生虫在宿主社会行为演化过程中所扮演的复杂角色。