Defense Date


Graduation Date

Summer 8-8-2020


One-year Embargo

Submission Type


Degree Name



Biological Sciences


Bayer School of Natural and Environmental Sciences

Committee Chair

Sarah K. Woodley

Committee Member

Benedict J. Kolber

Committee Member

Brady Porter

Committee Member

Michael Benard


neurology, acetylcholinesterase inhibitor, sublethal, nonmonotonic dose response, low dose effects, endpoint, frog, tadpole, Rana pipiens


In the US, over 1.1 billion pounds of pesticides are applied annually. Unfortunately, pesticides contaminate natural habitats affecting animal health. Chlorpyrifos (CPF) is an organophosphorous insecticide that contaminates surface waters. Few studies have assessed the impacts of CPF at low, ecologically realistic doses. I aimed to test the effects of low dose CPF exposures on biological parameters including body morphology, hormone levels, and brain development in Northern Leopard Frogs (Lithobates pipiens), a common vertebrate model. To determine if CPF exposure has direct impacts or indirectly impacts animals through the disruption of the food web, I examined CPF exposure on amphibian development in mesocosms with communities of CPF-sensitive or CPF-resistant zooplankton. I found CPF directly impacted brain shape. I then tested responses to the lowest, commonly encountered doses of CPF in a laboratory study and found changes in neurodevelopment, behavior, and neuroendocrine processes, demonstrating functional consequences of low-dose exposures in Northern Leopard Frogs. To determine if the hypothalamus-pituitary-adrenal/interrenal axis (HPA/I) and increased corticosterone (CORT) concentrations plays a role in these low-dose CPF exposures, I exposed tadpoles to either a vehicle control, CPF, CORT, or CPF+MTP (metyrapone [MTP], a CORT biosynthesis blocker). While CPF and CORT both impacted relative brain shape, they did so in different ways suggesting the effects of CPF were not being mediated through CORT. My dissertation provides a better understanding of how low, ecologically relevant concentrations of CPF are impacting vertebrate development, and provides new insights for conservation and management of animals living in organophosphate contaminated habitats.



Additional Citations

McClelland SJ, Bendis RJ, Relyea RA, and Woodley SK. 2018 Insecticide-induced changes in amphibian brains: How sublethal concentrations of chlorpyrifos directly affect neurodevelopment. Environmental Toxicology and Chemistry 37 (10): 2692-2698.

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Biology Commons