Effects of a Pathogen and Pesticides on Gray Treefrog (Hyla chrysoscelis) Metamorphosis and Survival

Abstract

Both the amphibian chytrid fungus Batrachochytrium dendrobatidis (Bd) and pesticides have been targeted as contributors to amphibian population declines. Declines have a worldwide distribution, but are only occurring in certain areas. Frequently, chytridiomycosis due to the Bd is treated as a uniform disease; however, recent evidence suggests variation among different isolates of Bd. Both Bd and pesticide effects on amphibians have been tested extensively individually, but few studies have attempted to test the interactive effects of these variables. In a lab study, we tested the effects of six different isolates of Bd, three from areas where amphibian population decline is occurring and three from areas where it is not, and two pesticides, the insecticide carbaryl and fungicide copper sulfate, on metamorphic responses and survival in Cope’s gray treefrog (Hyla chrysoscelis). We expected to see differing degrees of negative effects from the different types of Bd isolates. We expected to see negative effects from the carbaryl both alone and with Bd, but expected to see negative effects from copper sulfate only without Bd. Our results did not show any individual effects from Bd on metamorphic response or survival. We did find that carbaryl significantly increased mass at metamorphosis, time to metamorphosis, and time to tail absorption but did not significantly affect survival. Additionally, we found a significant interaction between pesticide and Bd on mass at metamorphosis. Our study does not indicate that environmental contaminants would make tadpoles more susceptible to Bd.