How time of exposure to the amphibian chytrid fungus affects hyla chrysoscelis in the presence of an insecticide
Effects of pathogens on host life-history characteristics can be influenced by changes in the immune system that occur during development as well as by environmental factors that negatively affect immune system function. Amphibians worldwide are experiencing population declines from chytridiomycosis caused by the fungal pathogen Batrachochytrium dendrobatidis. Disease outbreaks can be influenced by timing of exposure to B. dendrobatidis and by abiotic factors, such as pesticides, that could influence susceptibility. To examine the effects of larval pesticide exposure and timing of B. dendrobatidis exposure during development, we exposed Cope’s Gray Treefrogs (Hyla chrysoscelis) to the insecticide malathion throughout larval development and to B. dendrobatidis at 1 or 3 wk posthatching, or after metamorphosis. We reared tadpoles through metamorphosis and then for 28 d in the terrestrial environment to examine treatment effects on larval survival, time to metamorphosis, and mass at metamorphosis, as well as terrestrial survival and growth after metamorphosis. We found that malathion exposure resulted in a decrease in mass at metamorphosis and a decrease in terrestrial growth. Exposure to B. dendrobatidis did not influence larval development, terrestrial growth, or survival, and exposure to malathion appears to not have altered the effects of B. dendrobatidis exposure in a biologically significant way.