Understanding how human activities affect natural populations and communities is an important issue in environmental biology. Human impacts such as the release of abiotic stressors commonly co-occur with natural factors such as diseases, yet abiotic stress and wildlife diseases are commonly considered in isolation of each other. This project will investigate the effects of abiotic stress and wildlife diseases in concert. Amphibians offer an ideal system for studying the interaction of abiotic stress and diseases; they are experiencing global population declines and the presence of abiotic stressors and diseases have been implicated as causes. However, these two factors have largely been treated in isolation. This project will test the hypothesis that low concentrations of globally common abiotic stressors make amphibians more susceptible to two disease organisms that are causing tremendous mortality around the world. The objective of this project is to examine the separate and combined impacts of diseases and abiotic stressors on several species of amphibians. This work is transformative because it brings together three typically separate fields of research (physiological ecology, disease ecology, and community ecology) and unites them to tackle a major biological question. The proposed research has clear implications for understanding the role of abiotic stress and diseases in wildlife populations and for concerns about biodiversity in general. As a result, findings from this research have enormous potential implications for conservation and informing the regulation of abiotic stressors worldwide.
The broader impacts are multi-dimensional. The project will train several graduate and undergraduate students at two institutions, including under-represented groups. The benefits to society include new insights into the spread of infectious disease, with a focus on pathogens that are currently associated with worldwide amphibian declines. Hence, the potential impacts for improved amphibian conservation are enormous. The results will be disseminated in journals, conferences, seminars, web pages, and the popular press. The results also will be developed into Teacher Workshops and teaching modules for middle and high school teachers. Collectively, this work promises to have a substantial scientific impact as well as numerous broader impacts on society.
The goal of this research proposal was to investigate the potential for interactions between pesticides and a globally common disease in amphibians that is causing extinctions of dozens of species around the world. Our approach was to use mixtures of herbicides and insecticides at low, environmentally relevant concentrations at different stages of life in amphibians (e.g., as tadpoles and newly metamorphic frogs) followed by a subsequent exposure to the chytrid fungus. In a series of experiments, we found harmful effects of the pesticide mixtures and the fungus, but we rarely found harmful interactions of the two factors. In addition to this primary goal, we also were able to investigate several other related questions regarding pesticides and aquatic food webs. In the period of this NSF support of our research from 2012-2014, we produced a total of 34 published papers. We also have another 11 publications in review and more than a dozen papers in preparation. This work includes some major discoveries including a pattern of increased pesticide tolerance of amphibians and zooplankton living closer to agricultural fields and the first discovery in vertebrate animals that an exposure to a sublethal concentration of a pesticide can induce higher tolerance to the pesticide (and other pesticides) later in life.