Host genus and habitat use shape the distribution of Batrachochytrium dendrobatidis lineages in a hyper-diverse tropical amphibian community

Pathogens often exploit ecological and evolutionary opportunities created by anthropogenic change, with profound consequences for host communities. In Brazil’s Atlantic Forest, the amphibian chytrid fungus Batrachochytrium dendrobatidis (Bd) exemplifies this dynamic, with two co-occurring lineages: the enzootic Bd-Brazil lineage and the invasive Global Panzootic Lineage (Bd-GPL), implicated in historical amphibian declines and Bd hybridization events. To investigate how host taxonomy and habitat use influence Bd lineage distribution, we sampled 3,836 amphibians representing 42 species across paired aquatic and terrestrial transects over a two-year period. We successfully genotyped n = 252 out of 777 Bd-positive samples using nuclear and mitochondrial SNP assays to differentiate between Bd-GPL, Bd-Brazil, hybrids, and coinfections. Our results reveal that Bd lineage distribution is nonrandomly associated with host genus and habitat type. Stream-dwelling frogs, particularly those in the genus Hylodes, had higher rates of coinfection with Bd-GPL and Bd-Brazil than most other genera. This pattern may reflect their lifelong association with streams, which might increase their exposure to zoospores from multiple Bd lineages. In contrast, terrestrial transects were dominated by single-lineage Bd-GPL infections, even when accounting for differences in amphibian species composition and host genus among transect types. These findings suggest that aquatic habitats could serve as refugia for Bd-Brazil, while Bd-GPL may exhibit more desiccation tolerance. Methodological limitations of this study, including biases towards successfully genotyping high-load infections and limited genomic resolution, underscore the need for more high-resolution sequencing approaches to fully understand pathogen dynamics in the Atlantic Forest.病原体常可利用人为活动塑造的生态与进化契机，对宿主群落造成深远影响。在巴西大西洋森林中，两栖动物壶菌（Batrachochytrium dendrobatidis, Bd）便是这一动态过程的典型代表，其存在两种共存谱系：地方流行的Bd-Brazil谱系，以及具有入侵性的全球大流行谱系（Global Panzootic Lineage, Bd-GPL），后者与历史上两栖动物种群衰退以及Bd杂交事件密切相关。为探究宿主分类学特征与栖息地利用方式如何影响Bd谱系的分布格局，本研究在两年周期内，于配对设置的水生与陆生样带中采集了共计3836只两栖动物样本，涵盖42个物种。本研究通过核基因组与线粒体基因组单核苷酸多态性（Single Nucleotide Polymorphism, SNP）分型技术，成功对777份Bd检测阳性样本中的252份完成基因分型，以区分Bd-GPL、Bd-Brazil、杂交个体以及共感染样本。研究结果显示，Bd谱系的分布并非随机，而是与宿主属级分类单元以及栖息地类型存在显著关联。栖息于溪流中的蛙类，尤其是溪蟾属（Hylodes）物种，其Bd-GPL与Bd-Brazil共感染率高于多数其他宿主属。这一格局或与其终生依赖溪流生境有关——溪流环境可能会增加其接触多株Bd谱系游动孢子的概率。与之形成对比的是，陆生样带的感染以单一谱系的Bd-GPL为主，即便在控制样带间两栖动物物种组成与宿主属级差异的情况下亦是如此。上述研究结果表明，水生生境可能是Bd-Brazil的避难所，而Bd-GPL则可能具备更强的耐旱能力。本研究存在方法学局限，例如存在仅能成功对高载量感染样本完成基因分型的偏差，且基因组分辨率有限，这凸显了需采用更高分辨率的测序技术，方能全面解析大西洋森林中的病原体动态。