Chytrid infection dynamics in frog populations from climatically disparate regions

Batrachochytrium dendrobatidis (Bd), the causative agent of chytridiomycosis and the leading cause of amphibian declines across the globe, is sensitive to temperature and thought to be restricted to certain climatic regions as a result. This study sought to assess the prevalence and intensity of chytridiomycosis among populations of a widespread frog species, Litoria raniformis, in cool temperate and semi-arid regions. We show that chytrid can infect amphibian populations well beyond its predicted geographic range, although infection prevalence was three times lower and maximum infection intensity was seven times lower in semi-arid sites relative to temperate ones. Strong seasonal patterns for both prevalence and intensity were identified in each region. Consistent environmental drivers were also identified, including water temperature, wetland salinity and pH. This is the first study to report a quadratic effect of pH on chytrid prevalence in the field, as expected from laboratory studies. Empirical data on the distribution and key environmental drivers of chytrid infections is vital to identify environmental refuges from the pathogen, and to guide management to reduce disease impact.