1. Contaminants such as mercury are pervasive and can have immunosuppressive effects on wildlife. Impaired immunity could be important for forecasting pathogen spillover, as many land‐use changes that generate mercury contamination also bring wildlife into close contact with humans and domestic animals. However, the interactions among contaminants, immunity and infection are difficult to study in natural systems, and empirical tests of possible directional relationships remain rare.
2. We capitalized on extreme mercury variation in a diverse bat community in Belize to test association among contaminants, immunity and infection. By comparing a previous dataset of bats sampled in 2014 with new data from 2017, representing a period of rapid agricultural land conversion, we first confirmed bat species more reliant on aquatic prey had higher fur mercury. Bats in the agricultural habitat also had higher mercury in recent years. We then tested covariation between mercury and cellular immunity and determined if such relationships mediated associations between mercury and bacterial pathogens. As bat ecology can dictate exposure to mercury and pathogens, we also assessed species‐specific patterns in mercury–infection relationships.
3. Across the bat community, individuals with higher mercury had fewer neutrophils but not lymphocytes, suggesting stronger associations with innate immunity. However, the odds of infection for haemoplasmas and Bartonella spp. were generally lowest in bats with high mercury, and relationships between mercury and immunity did not mediate infection patterns. Mercury also showed species‐ and clade‐specific relationships with infection, being associated with especially low odds for haemoplasmas in Pteronotus mesoamericanus and Dermanura phaeotis. For Bartonella spp., mercury was associated with particularly low odds of infection in the genus Pteronotus but high odds in the subfamily Stenodermatinae.
4. Synthesis and application. Lower general infection risk in bats with high mercury despite weaker innate defense suggests contaminant‐driven loss of pathogen habitat (i.e. anemia) or vector mortality as possible causes. Greater attention to these potential pathways could help disentangle relationships among contaminants, immunity and infection in anthropogenic habitats and help forecast disease risks. Our results also suggest that contaminants may increase infection risk in some taxa but not others, emphasizing the importance of considering surveillance and management at different phylogenetic scales.

中文翻译：

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新热带蝙蝠群落中汞，免疫力和感染之间相互作用的相互作用

1. 诸如汞之类的污染物无处不在，并对野生生物具有免疫抑制作用。免疫力受损对于预测病原体外溢可能很重要，因为许多会引起汞污染的土地利用变化也会使野生生物与人类和家畜紧密接触。但是，很难在自然系统中研究污染物，免疫力和感染之间的相互作用，并且对可能的方向关系进行实证检验仍然很少。
2. 我们利用伯利兹多样化蝙蝠社区中汞的极端变异来测试污染物，免疫力和感染之间的关联。通过将2014年采样的蝙蝠的先前数据集与2017年的新数据（代表一个快速的农业土地转换时期）进行比较，我们首先确认了更依赖水生猎物的蝙蝠物种具有较高的毛皮汞含量。近年来，农业栖息地中的蝙蝠中的汞含量也更高。然后，我们测试了汞与细胞免疫之间的协变，并确定了这种关系是否介导了汞与细菌病原体之间的关联。由于蝙蝠的生态学可以决定汞和病原体的暴露程度，因此我们还评估了汞与感染关系中特定物种的模式。
3. 在整个蝙蝠群落中，汞含量较高的个体中性粒细胞较少，但淋巴细胞却较少，这表明它们与先天免疫力的关联更强。但是，血友病和Bartonella spp感染的几率很高。在汞含量高的蝙蝠中，汞含量通常最低，汞与免疫力之间的关系并未介导感染模式。汞还显示出物种和进化枝特有的与感染的关系，这与中翼疫霉菌和噬菌体中的血友病几率特别低有关。对于巴尔通体属，汞用在属感染的特别低的可能性相关联裸背蝠属但亚科Stenodermatinae高几率。
4. 综合与应用。尽管先天防御能力较弱，但汞含量高的蝙蝠的一般感染风险较低，这表明可能是由污染物驱动的病原体栖息地丧失（即贫血）或病媒死亡。对这些潜在途径的更多关注可以帮助弄清人为栖息地中污染物，免疫力和感染之间的关系，并有助于预测疾病风险。我们的研究结果还表明，污染物可能会增加某些分类单元的感染风险，而不会增加其他分类单元的感染风险，从而强调了在不同的系统发生尺度上考虑进行监视和管理的重要性。