Data from: Is exposure to chytrid fungus and ranavirus higher in ponds invaded by American bullfrogs?

Data associated with manuscript: https://doi.org/10.1007/s10530-025-03648-8The spread of emerging infectious diseases (EIDs) and non-native invasive species are interconnected processes driving biodiversity loss. A key example involves Batrachochytrium dendrobatidis (Bd) and ranavirus (Rv), pathogens contributing to global amphibian declines. Their occurrence has been linked to invasive American bullfrogs (Lithobates catesbeianus) serving as asymptomatic vectors. To determine the relationship between Bd and Rv exposure and bullfrogs, we investigated whether pathogen occurrence and environmental loads are correlated with the presence and density of bullfrogs and whether the seasonal variation in Bd exposure is related to bullfrog phenology. We sampled 157 ponds in Belgium, including four with known bullfrog and Bd presence that were monitored monthly for two years, using quantitative environmental DNA (eDNA) barcoding. We validated a duplexed assay that simultaneously targets Bd and Rv, and we quantified eDNA concentrations of bullfrogs, Bd, and Rv serving as proxies for density and pathogen loads. Bd was detected more frequently when bullfrogs were present and both the frequency of detection and environmental loads of Bd increased in ponds with high bullfrog densities. In contrast, Rv detection likelihood and load were not significantly related to bullfrog presence or density. Seasonal fluctuations in Bd loads varied between ponds with and without breeding activity. In the former, Bd was consistently detected, likely due to overwintering tadpoles. In the latter, Bd loads varied throughout the year, with peak loads coinciding with juvenile immigration. Collectively, our findings indicate that amphibian exposure to Bd, but not Rv, is higher in areas and periods where bullfrogs are present and occur at high densities本数据集关联的论文手稿：https://doi.org/10.1007/s10530-025-03648-8。新兴传染病（Emerging Infectious Diseases, EIDs）与非本土入侵物种的扩散是驱动生物多样性丧失的相互关联过程。其中极具代表性的案例当属蛙壶菌（Batrachochytrium dendrobatidis, Bd）与蛙病毒（ranavirus, Rv）——这两类病原体是导致全球两栖动物种群衰退的关键因素。二者的检出与作为无症状传播媒介的入侵性美洲牛蛙（Lithobates catesbeianus）密切相关。为明确Bd、Rv暴露情况与牛蛙之间的关联，本研究探究了病原体的存在状态与环境载量是否与牛蛙的分布及其种群密度存在相关性，同时分析了Bd暴露的季节变化是否与牛蛙的物候特征存在关联。我们在比利时境内共采样157个池塘，其中4个已知存在牛蛙与Bd的池塘被连续两年按月监测，检测方法采用定量环境DNA（environmental DNA, eDNA）条形码技术。我们验证了一种可同时靶向Bd与Rv的双重检测体系，并通过量化牛蛙、Bd及Rv的eDNA浓度，分别作为牛蛙种群密度与病原体环境载量的替代指标。结果显示，当池塘中存在牛蛙时，Bd的检出频率更高；且在牛蛙种群密度较高的池塘中，Bd的检出频率与环境载量均显著提升。与之相对，Rv的检出可能性与环境载量均未与牛蛙的存在或种群密度呈现显著相关性。Bd载量的季节波动在存在牛蛙繁殖活动与无繁殖活动的池塘中存在显著差异：在存在繁殖活动的池塘中，Bd可被持续检出，这一现象或与越冬蝌蚪有关；而在无繁殖活动的池塘中，Bd载量全年呈现波动，其峰值与牛蛙幼体迁入的时间相吻合。综合来看，本研究结果表明，两栖动物暴露于Bd的风险在牛蛙存在且种群密度较高的区域与时期显著升高，而暴露于Rv的风险则无此关联。