Data from: Linking genetic and environmental factors in amphibian disease risk

A central question in evolutionary biology is how interactions between organisms and the environment shape genetic differentiation. The pathogen Batrachochytrium dendrobatidis (Bd) has caused variable population declines in the lowland leopard frog (Lithobates yavapaiensis), thus disease has potentially shaped, or been shaped by, host genetic diversity. Environmental factors can also influence both amphibian immunity and Bd virulence, confounding our ability to assess genetic effects on disease dynamics. Here, we used genetics, pathogen dynamics, and environmental data to characterize L. yavapaiensis populations, estimate migration, and determine relative contributions of genetic and environmental factors in predicting Bd dynamics. We found that the two uninfected populations belonged to a single genetic deme, whereas each infected population was genetically unique. We detected an outlier locus that deviated from neutral expectations and was significantly correlated with mortality within populations. Across populations, only environmental variables predicted infection intensity, whereas environment and genetics predicted infection prevalence, and genetic diversity alone predicted mortality. At one locality with geothermally elevated water temperatures, migration estimates revealed source-sink dynamics that have likely prevented local adaptation. We conclude that integrating genetic and environmental variation among populations provides a better understanding of Bd spatial epidemiology, generating more effective conservation management strategies for mitigating amphibian declines.

进化生物学的核心议题之一，在于生物与环境间的相互作用如何塑造遗传分化。病原真菌蛙壶菌（Batrachochytrium dendrobatidis，简称Bd）曾导致低地豹蛙（Lithobates yavapaiensis）出现程度不等的种群衰退，因此病害既可能塑造宿主的遗传多样性，亦可能受宿主遗传多样性的调控。环境因子同时可影响两栖动物的免疫能力与Bd的毒力，这会干扰我们评估遗传效应对病害动态的影响。本研究借助遗传学数据、病原动态数据与环境数据，对低地豹蛙（Lithobates yavapaiensis）的种群特征进行解析，估算种群迁移情况，并明确遗传与环境因子在预测Bd动态中的相对贡献。研究发现，两个未感染种群同属一个遗传居群（genetic deme），而每个感染种群均具有独特的遗传特征。我们检测到一个偏离中性预期的异常位点，其与种群内的死亡率存在显著相关性。跨种群分析显示，仅环境变量可预测感染强度；感染流行率可由环境与遗传因子共同预测；而死亡率则仅能通过遗传多样性进行预测。在一处水温因地热活动升高的采样点，迁移估算结果揭示了源-汇动态（source-sink dynamics），这一动态或已阻碍了当地的适应性进化。本研究表明，整合种群间的遗传与环境变异，能够更深入地解析Bd的空间流行病学特征，进而为缓解两栖动物种群衰退制定更高效的保护管理策略。