IMPACTS OF ENVIRONMENTAL STRESSORS ON NATIVE SOUTH DAKOTA AMPHIBIAN PHYSIOLOGY AND SURVIVAL

Amphibian populations around the world are declining, with some of the most likely drivers behind these declines including emerging infectious diseases and environmental contaminants. To address major gaps in the current literature, I sought to evaluate the effect of two major environmental stressors on various aspects of amphibian physiology: emerging infectious diseases and environmental contaminants. Emerging infectious diseases of amphibians include fungal, viral, and parasitic pathogens which have expanded in host range, either geographically or in competent host species. Environmental contaminants include chemicals which may be naturally occurring in the environment, or which may be introduced to the environment, often as a result of anthropogenic influences. First, this research documented the geographic range of ranavirus in South Dakota during a 3-year period. Through intensive field surveillance, I confirmed the first positive detection of ranavirus in South Dakota amphibians and determined which species serve as ranavirus hosts, including two state listed heritage species. Following the documentation of ranavirus in South Dakota, this research confirmed that aquatically overwintering larval American bullfrogs (Rana catesbeiana) are competent ranavirus reservoir hosts that can maintain infection throughout the winter, indicating the ability to transmit ranavirus to conspecifics during the winter. The confirmation of American bullfrogs as ranavirus reservoirs addresses a major gap in the current literature. Next, I determined that infection with the parasitic pathogen anchor worms (Lernaea cyprinacea) resulted in higher rates of mortality than ranavirus infection alone, with co-infection by these pathogens resulting in the same mortality rate as single infection by anchor worms. Finally, to further evaluate the effects of pathogens on amphibian physiology and resilience, I investigated the combined effects of the fungal pathogen Batrachochytrium dendrobatidis and the environmental contaminant selenium. Here, I determined that the combination of these stressors can influence selenium accumulation in the liver and leg muscle tissues and can reduce heart function in recently metamorphosed amphibians, the first documentation of sublethal effects of these stressors in amphibians. Overall, this research used a combination of approaches from ecophysiology, disease ecology, and ecotoxicology to evaluate a wide range of environmental stressors and their impacts on native South Dakota amphibians