Abstract
Host-pathogen specificity can arise from certain selective environments mediated by both the host and pathogen. Therefore, understanding the degree to which host species identity is correlated with pathogen genotype can help reveal historical host-pathogen dynamics. One animal disease of particular concern is chytridiomycosis, typically caused by the global panzootic lineage of the amphibian chytrid fungus (Batrachochytrium dendrobatidis, Bd), termed Bd-GPL. This pathogen lineage has caused devastating declines in amphibian communities around the world. However, the site of origin for the common ancestor of modern Bd-GPL and the fine-scale transmission dynamics of this lineage have remained a mystery. This is especially the case in North America where Bd-GPL is widespread, but disease outbreaks occur sporadically. Herein, we use Bd genetic data collected throughout the United States from amphibian skin swabs and cultured isolate samples to investigate Bd genetic patterns. We highlight two case studies in Pennsylvania and Nevada where Bd-GPL genotypes are strongly correlated with host species identity. Specifically, in some localities bullfrogs (Rana catesbeiana) are infected with Bd-GPL lineages that are distinct from those infecting other sympatric amphibian species. Overall, we reveal a previously unknown association of Bd genotype with host species and identify the eastern United States as a Bd diversity hotspot and potential site of origin for Bd-GPL.
Highlights
MethodsSample collection in northwestern Pennsylvania and southern NevadaWe collected Bd samples in Pymatuning Lab of Ecology (PA) between 2017–2019 and in NV between 2016–2018
When host-pathogen specificity exists within a system it can serve to reveal historical disease dynamics and has consequences for the evolution of virulence
We found a repeated pattern of Bd genetic structure that is most closely associated with amphibian host species in both Pymatuning Lab of Ecology (PA) and NV
Summary
Sample collection in northwestern Pennsylvania and southern NevadaWe collected Bd samples in PA between 2017–2019 and in NV between 2016–2018. Additional ethics approval for work done in Pennsylvania was granted through the Department of Defense ACURO system (protocol number SERDP-RC-2638.03). Permission to sample in Nevada was given by Bureau of Land Management, US Department of Interior (for Desert National Wildlife Range), Nevada Division of State Parks (for Spring Mountain Ranch State Park), and Nevada Department of Wildlife (for Lake Mead National Recreation Area). In both areas, we captured frogs by hand using clean nitrile gloves. We extracted DNA from swabs in PA using the Qiagen DNEasy Blood and Tissue kit (Qiagen, Valencia, USA), and from NV using PrepMan Ultra [21], following both manufacturer’s protocols
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