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Beyond the swab: ecosystem sampling to understand the persistence of an amphibian pathogen


Understanding the ecosystem-level persistence of pathogens is essential for predicting and measuring host–pathogen dynamics. However, this process is often masked, in part due to a reliance on host-based pathogen detection methods. The amphibian pathogens Batrachochytrium dendrobatidis (Bd) and B. salamandrivorans (Bsal) are pathogens of global conservation concern. Despite having free-living life stages, little is known about the distribution and persistence of these pathogens outside of their amphibian hosts. We combine historic amphibian monitoring data with contemporary host- and environment-based pathogen detection data to obtain estimates of Bd occurrence independent of amphibian host distributions. We also evaluate differences in filter- and swab-based detection probability and assess inferential differences arising from using different decision criteria used to classify samples as positive or negative. Water filtration-based detection probabilities were lower than those from swabs but were > 10%, and swab-based detection probabilities varied seasonally, declining in the early fall. The decision criterion used to classify samples as positive or negative was important; using a more liberal criterion yielded higher estimates of Bd occurrence than when a conservative criterion was used. Different covariates were important when using the liberal or conservative criterion in modeling Bd detection. We found evidence of long-term Bd persistence for several years after an amphibian host species of conservation concern, the boreal toad (Anaxyrus boreas boreas), was last detected. Our work provides evidence of long-term Bd persistence in the ecosystem, and underscores the importance of environmental samples for understanding and mitigating disease-related threats to amphibian biodiversity.

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We thank the members of The Boreal Toad Recovery Team for their support of this project and for their assistance with environmental and swab sample collection. We thank K. Davenport, The Bailey Lab, The Huyvaert Lab, The Grant Lab, W. C. Funk (Colorado State University), E. Muths (USGS), L. Belden, and one anonymous reviewer for providing valuable comments on earlier drafts of this manuscript. This is contribution number 650 of the USGS Amphibian Research and Monitoring Initiative (ARMI).

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BAM, KPH, and LLB conceived of the study, BAM conducted the statistical analyses, and BAM, KPH, and LLB wrote the manuscript.

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Correspondence to Brittany A. Mosher.

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Communicated by Lisa Belden.

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Mosher, B.A., Huyvaert, K.P. & Bailey, L.L. Beyond the swab: ecosystem sampling to understand the persistence of an amphibian pathogen. Oecologia 188, 319–330 (2018).

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