New research from Geoff Heard and colleagues demonstrates that the impact of chytridiomycosis (a disease caused by amphibian chytrid fungus) on populations of growling grass frogs (Litoria raniformis, an endangered species) is mediated by wetland microclimate and water chemistry. Prevalence of the disease is considerably lower in warm and saline wetlands.
It’s known from previous work (on this system and others) that the prevalence and intensity of chytrid infections declines with increasing temperature and salinity (because chytrid is sensitive to both), but this new study is the first to demonstrate that these relationships have important implications for the persistence of frogs threatened by chytrid, a disease that is driving declines in over 200 species of frog around the word.
Using 11 years of monitoring data, the researchers have shown that populations of growlers in warmer, saltier wetlands have a higher chance of persistence through time because the prevalence of infections is low. Moreover, they have shown that some metapopulations of growlers are unlikely to survive without these warmer, saltier wetlands; that is, without their refuges from disease.
Metapopulation persistence in fragmented landscapes depends on habitat patches that can support resilient local populations and sufficient connectivity between patches. Yet epidemiological theory for metapopulations has largely overlooked the capacity of particular patches to act as refuges from disease, and has suggested that connectivity can undermine persistence. This study shows that relatively warm and saline wetlands are environmental refuges from chytridiomycosis for an endangered Australian frog, and act jointly with connectivity to sustain frog metapopulations.
Heard GW, CD Thomas, JA Hodgson, MP Scroggie, DSL Ramsey & N Clemann (2015). Refugia and connectivity sustain amphibian metapopulations afflicted by disease. Ecology Letters 18: 853–863.