Visiting Assistant Professor of Biology
University of Pittsburgh at Johnstown
Do pesticides interact with pathogens?
Amphibian populations across the globe are declining at an unprecedented rate and our lab is focused on determining what the causal factors for this decline might be. A wide variety of pesticides have been shown to be directly cause mortality in amphibian populations, but often the concentrations used in these studies are not environmentally relevant. Pathogens and parasites have also been implicated in this decline. In particular, the amphibian chytrid fungus (Batrachochytrium dendrobatidis or Bd) has been shown to cause marked mortality among amphibian populations and can be implicated in the demise of nearly 300 species of amphibians. Often when these stressors are studied in the lab they are examined individually, but in nature these amphibians are often exposed to both stressors simultaneously.
With the Blaustein lab (Oregon State University), we have performed a series of experiments examining whether or not pesticides and Bd can interact to make amphibians more suceptible to either, or potentially both, factors. In the first study, amphibians were exposed to sublethal concentrations of mixtures of insecticides or herbicides as either larvae or metamorphs and were then subsequently subjected to Bd treatments. In a follow-up study, we subjected amphibians to both stressors simultaneously. Then we tracked survivorship for several species of amphibians both from the eastern and western United States.
What role do bullfrogs play in the spread of Bd?
The original range of the American bullfrog (Lithobates catesbeianus) was along the southern and eastern portion of the United States and Canada, but due to pet trade and the import of bullfrogs as tadpoles, it has since made its way to the western part of the United States where it is now considered to be an invasive species. This large species of amphibian can often outcompete other amphibians and has been directly involved in the decline of several species including the California red-legged frog. Bullfrogs have also been implicated in bringing Bd with them from its native range into the western US. This species is widely believed to be a carrier of the disease because it was thought to be not suceptible to the pathogen itself. While this has largely been refuted, it is still believed that bullfrogs (which overwinter as a tadpoles) can maintain potentially maintain the Bd infection over this period of time and then reinfect other spring breeding amphibians when it emerges as the pond thaws out.
In another collaborative project with the Blaustein lab, we have examined the effects of Bd strain and bullfrog presence on infection occurrence in several spring breeding amphibians from the western US to either refute or support the claim of bullfrogs being vectors for the spread of Bd.