Influence of Batrachochytrium dendrobatidis isolate and dose on infection outcomes in a critically endangered Australian amphibian

The amphibian chytrid fungus ( Batrachochytrium dendrobatidis ( Bd )) is a continuing threat globally, causing widespread declines. Corroboree frogs ( Pseudophryne corroboree ) are critically endangered and no longer have self-sustaining populations in the wild due to the presence of Bd in the environment. We aimed to investigate variation in susceptibility to Bd in juvenile P. corroboree and evaluate the impact of Bd isolate and dose on infection outcomes. We experimentally exposed juvenile P. corroboree to two Bd isolates at five doses, and also characterised the in vitro growth of these isolates. Frogs showed high susceptibility to Bd , with isolate and dose impacting survival time and infection loads. Additionally, differences in the in vitro phenotype of the two Bd isolates were linked to their differential virulence. This study highlights the considerable impact that fungal isolate and dose have in shaping disease outcomes in experimental exposures.