Effects of agricultural pesticides and chytrid fungus Batrachochytrium dendrobatidis on the health of post-metamorphic northern leopard frogs (Lithobates pipiens)

Numerous studies have shown that pesticides can adversely affect amphibian health and suppress immune function, making them more susceptible to pathogens and disease. This study assessed the independent and combined effects of exposure to two agricultural herbicides and the pathogenic fungus Batrachochytrium dendrobatidis (Bd ) on the health and survival of post-metamorphic northern leopard frogs (Lithobates pipiens ). Wild-caught frogs were exposed to the herbicides atrazine (Aatrex® Liquid 480) or glyphosate (Roundup® Original) for 21 days and subsequently challenged with Bd . The glyphosate formulation significantly reduced growth compared to controls during the pesticide exposure. The atrazine formulation significantly reduced gain in mass at 94 days post initial exposure to the pesticides. No treatment significantly affected survival, the numbers of leucocytes, the hepatosomatic index, the splenosomatic index, the numbers and sizes of melanomacrophage aggregates in the liver or spleen, or the numbers and sizes of granulomas in the liver. Histological tests revealed no evidence of Bd infection in any Bd -exposed frogs, while molecular tests (real-time PCR) detected only one case of light infection (1.6 DNA copies) in an atrazine- and Bd -exposed frog. Frogs exposed to Bd shed their skin significantly more frequently than Bd -unexposed frogs, which may have helped them resist or clear infection. Overall, the results suggest that these frogs were resistant to Bd and that pre-exposure to the pesticides did not alter this resistance. However, reduced growth can lower the reproductive success and survival of amphibians, and therefore, exposure to the pesticides may contribute to population reductions in leopard frogs