Environmental gradients explaining the prevalence and intensity of infection with the amphibian chytrid fungus: the host's perspective

Chydridiomycosis is an infectious emerging disease in amphibians that has been directly linked to mass mortality, drastic population decline and extinction. The understanding of the factors limiting the distribution and the abundance of its biological agent, the amphibian chytrid fungus Batrachochytrium dendrobatidis (Bd ), is still limited. It has been suggested that climate plays a key role. A recent study conducted infection surveys at 31 lowland sites on the Australian East coast and searched for climatic variables explaining Bd prevalence and intensity in Stony creek frogs Litoria lesueuri (complex). A link between the prevalence of infections and latitude was advocated, exclusively focusing on the pathogen. Beyond this, the prevalence and intensity of Bd infection may also depend on the climatic suitability of a given site for the amphibian host. Herein, we extend the previous study using a set of long-term bioclimatic variables and assess climatic suitability for Stony creek frogs at the sites previously studied for Bd. We ran a Climatic Envelope Model for our target amphibian based on those variables with the most explanatory power for prevalence and intensity, thus representing the link between climatic suitability for both the pathogen and the host. Our findings allow the hypothesis that there exists a significant correlation between climatic suitability for Stony creek frogs at the previously studied sites and latitude. At the same time, this was congruent with the latitudinal gradient of the number of zoospores per frog.