Differential patterns of Batrachochytrium dendrobatidis infection in relict amphibian populations following severe disease-associated declines

Abstract

Global amphibian biodiversity has declined dramatically in the past 4 decades, and many amphibian species have declined to near extinction as a result of emergence of the amphib- ian chytrid fungus, Batrachochytrium dendrobatidis (Bd). However, persistent or recovering pop- ulations of several amphibian species have recently been rediscovered, and such populations may illustrate how amphibian species that are highly susceptible to chytridiomycosis may survive in the presence of Bd. We conducted field surveys for Bd infection in 7 species of Costa Rican amphib- ians (all species that have declined to near extinction but for which isolated populations persist) to characterize infection profiles in highly Bd-susceptible amphibians post-decline. We found highly variable patterns in infection, with some species showing low prevalence (~10%) and low infec- tion intensity and others showing high infection prevalence (>80%) and either low or high infec- tion intensity. Across sites, infection rates were negatively associated with mean annual precipita- tion, and infection intensity across sites was negatively associated with mean average temperatures. Our results illustrate that even the most Bd-susceptible amphibians can persist in Bd-enzootic eco- systems, and that multiple ecological or evolutionary mechanisms likely exist for host−pathogen co-existence between Bd and the most Bd-susceptible amphibian species. Continued monitoring of these populations is necessary to evaluate population trends (continuing decline, stability, or population growth). These results should inform efforts to mitigate impacts of Bd on amphibians in the field.