Within host populations, individuals can vary in their susceptibility to infections and in the severity and progression of disease once infected. Though mediated through differences in behaviour, resistance or tolerance, variation in disease outcomes ultimately stems from genetic and environmental (including social) factors. Despite obvious implications for the evolutionary, ecological and epidemiological dynamics of disease traits, the relative importance of these factors has rarely been quantified in naturally infected wild animal hosts. Here, we use a long-term capture-mark-recapture study of group-living European badgers (Meles meles) to characterize genetic and environmental sources of variation in host infection status by Mycobacterium bovis, the causative agent of bovine tuberculosis (bTB). We find that genetic factors contribute to M. bovis infection status, whether measured over a lifetime or across repeated captures. In the latter case, the heritability (h2 ) of infection status is close to zero in cubs and yearlings but increases in adulthood. Overall, environmental influences arising from a combination of social group membership (defined in time and space) and maternal effects appear to be more important than genetic factors. Thus, while genes do contribute to among-individual variation, they play a comparatively minor role, meaning that rapid evolution of host defences under parasite-mediated selection is unlikely (especially if selection is on young animals where h2 is lowest). Conversely, our results lend further support to the view that social and early-life environments are important drivers of the dynamics of bTB infection in badger populations specifically, and of disease traits in wild hosts more generally.

中文翻译：

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欧洲獾（Meles meles）牛分枝杆菌感染状态的遗传、社会和母体贡献。

在宿主群体中，个体对感染的易感性以及感染后疾病的严重程度和进展可能会有所不同。虽然通过行为、抵抗力或耐受性的差异介导，但疾病结果的变化最终源于遗传和环境（包括社会）因素。尽管对疾病特征的进化、生态和流行病学动态有明显的影响，但这些因素的相对重要性在自然感染的野生动物宿主中很少被量化。在这里，我们使用群居欧洲獾（Meles meles）的长期捕获标记重新捕获研究来表征牛分枝杆菌（牛结核病（bTB）的病原体）宿主感染状态变异的遗传和环境来源。我们发现遗传因素对 M. 牛感染状态，无论是在一生中还是在重复捕获中进行测量。在后一种情况下，幼崽和一岁幼崽的感染状态的遗传力 (h2) 接近于零，但在成年后会增加。总体而言，由社会群体成员资格（在时间和空间上定义）和母体效应相结合产生的环境影响似乎比遗传因素更重要。因此，虽然基因确实有助于个体间变异，但它们的作用相对较小，这意味着寄主防御在寄生虫介导的选择下的快速进化是不可能的（特别是如果选择是在 h2 最低的年轻动物上进行的）。相反，我们的结果进一步支持以下观点，即社会和早期生活环境是獾种群 bTB 感染动态的重要驱动因素，特别是，