Heated Aquatic Shelters Reduce Infection Intensity but Not Prevalence of a Fungal Pathogen in Common Toad Tadpoles

ABSTRACT The development of in situ applicable mitigation methods against diseases is an area in conservation biology that deserves more attention. The chytrid fungus Batrachochytrium dendrobatidis (Bd) causes chytridiomycosis, an infectious disease in amphibians. Although it is responsible for population declines and extinctions worldwide, no widely applicable mitigation method is available against the disease. The fungus has a lower thermal tolerance than most amphibian species, which raises the possibility of curing individuals with thermal treatments, an alternative that is likely safer to use under natural conditions than chemicals. Amphibians, being ectothermic animals, actively seek warm environments, so presenting them with the possibility of reaching their preferred body temperatures may be a mild but effective mitigation intervention. In this study, we tested whether providing a heated shelter for Bd‐exposed common toad ( Bufo bufo ) tadpoles, kept under seminatural conditions at different densities, helps the individuals to eliminate the infection or reduce its costs. We found that providing tadpoles with access to heated shelters decreased the intensity but not the prevalence of Bd‐infection, and that the density of tadpoles did not alter the beneficial effect of the treatment. The mean body mass of individuals was lowered when tadpoles were kept at high density, but the availability of heated shelters did not have an effect on the body mass of individuals. Our results suggest that the application of heated microrefugia may help Bd‐infected common toad tadpoles overcome the disease, but the device itself and its application both need further improvements. The use of heated shelters could become a cheap and widely applicable method for the in situ treatment of chytridiomycosis and other waterborne, cold‐adapted pathogens in nature conservation.