The distribution and population persistence of many North American amphibians depends on environmental factors at multiple spatial scales. Anthropogenic and naturally occurring stressors, including contaminants, predators, and pond-drying, have been shown to affect amphibian growth, development, and health. The herbicide atrazine (2-chloro-4-ethylamino-6-isoproyl-amino-s-triazine) is a widely used pesticide in the U.S., and in some amphibians has been shown to reduce size and health at metamorphosis and alter gonadal function, presumably through endocrine disruption. Environmental changes predicted by climate models could exacerbate these impacts, as well as directly affect amphibian development and population persistence through accelerated pond-drying and habitat loss or modification. Objectives of this project were to: 1) Quantify developmental responses to the combined effects of atrazine exposure and accelerated pond-drying rates; and 2) Quantify potential effects of these and other environmental stressors on amphibian occurrence and health. Growth, development, and physiological state (skeletal/eye malformations and gonadal development) were assessed in northern leopard frog (<italic>Rana pipiens</italic>) and wood frog (<italic>Rana sylvatica</italic>) in experimental exposures and field surveys in the U.S. Prairie Pothole Region across a range of environmentally relevant atrazine concentrations (0.1, 20, and 200 μg/L) and in combination with climate change and other environmental factors suspected to affect amphibian larval development. Atrazine exposure during larval development decreased survival and had sub-lethal impacts on growth and development, which could negatively impact populations by reducing annual recruitment and survival of juveniles. Presence, abundance, and severity of testicular oocytes (TOs) did not appear to be related to atrazine exposure in experimental or field specimens; however, TO prevalence differed greatly between species (>40% in <italic>R. pipiens</italic> and <5% in <italic>R. sylvatica</italic>). These results suggest that TOs are not likely due solely to endocrine disruption by atrazine and more research is needed to understand reproductive or population-level impacts of TOs. Amphibian metrics (presence, breeding, skeletal malformations, and TOs) responded differently to environmental variables from wetland, local, and landscape scales, and amphibian breeding (presence or success) was identified as a better indicator of environmental condition than species presence, calling, or TOs.
University of Minnesota Ph.D. dissertation. April 2014. Major: Integrated Biosciences. Advisor: Lucinda Johnson. 1 computer file (PDF); xiv, 222 pages.
Effects of atrazine and climate change on amphibian larval development and growth.
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