Data from: Social context alters host behavior and infection risk

Variation in infection risk and transmission potential are widespread in human and wildlife diseases and play a central role in host-pathogen dynamics. To explain this variation, most studies focus on linking host traits to differences in pathogen exposure, infection, and transmission, but typically do not to account for hosts’ social context. Yet, an individual’s risk of acquiring infection is likely influenced jointly by their own traits and their social environment. Here, we use three natural genotypes of the fruit fly Drosophila melanogaster to test how variation in pathogen transmission is linked to differences in host behavior and social context. We constructed groups of 12 flies from one of three different genotypes and five different sex ratios (0%, 33%, 50%, 67%, or 100% female) in a fully factorial design. To each group we added a male or female “primary case” fly that had been exposed to the generalist fungal entomopathogen Metarhizium robertsii. We then recorded groups’ aggregation behavior, mating frequency, and infection prevalence. Aggregation and mating behavior were influences either jointly or additively by fly genotype and sex ratio. However, a combination of individual-level (mating history; the sex of the primary case) and group-level factors (sex ratio) jointly influenced individuals’ infection risk. There were more infections in female-biased groups, though the sex of the primary case also influenced sex-biased mortality and the relationship between individuals’ mating history and infection risk. Thus, an individual’s social environment can be an important predictor of social dynamics and their survival outcomes.感染风险与传播潜力的变异广泛存在于人类与野生动物疫病体系中，在宿主-病原体动态（host-pathogen dynamics）中发挥核心作用。为解释这类变异，绝大多数相关研究多将宿主性状与病原体暴露、感染及传播的差异建立关联，但通常未纳入宿主的社会背景因素进行分析。然而，个体的感染获得风险实则同时受自身性状与所处社会环境的共同调控。本研究以携带三种自然基因型的黑腹果蝇（Drosophila melanogaster）为实验对象，旨在探究病原体传播变异与宿主行为、社会背景之间的关联机制。我们采用全因子设计（fully factorial design）构建实验种群：每组包含12只果蝇，其来源涵盖3种基因型之一与5种性比梯度（0%、33%、50%、67%或100%雌性）。向每组种群中接入1只经广谱昆虫病原真菌罗伯茨绿僵菌（Metarhizium robertsii）预暴露处理的雄性或雌性原发感染个体（primary case）。随后我们记录了各组的聚集行为、交配频率以及感染率（infection prevalence）。果蝇的基因型与性比对聚集行为和交配行为存在联合效应或加性效应。但个体层面因素（交配史、原发感染个体的性别）与群体层面因素（种群性比）的组合，共同作用于个体的感染风险。在雌性占比偏高的实验种群中，感染个体数量更多；不过原发感染个体的性别同样会影响种群的性别偏向性死亡率，以及个体交配史与感染风险之间的关联。综上，个体所处的社会环境可作为种群社会动态与个体存活结局的重要预测因子。