Date of Award
Master of Science (MS)
Robert A. Newman
Worldwide reports of population declines and extinctions of amphibians have continued for at least two decades. Factors frequently reported in association with these declines include habitat loss, infectious diseases, and environmental degradation. Three sources of disease have been a concern for amphibians: chytrid fungus, Ranavirus, and some helminth parasites. Much of the existing reporting on disease results from anecdotal accounts associated with localized outbreaks, but understanding the scope and dynamics of infectious agents in host populations requires a regional perspective. My objectives were to estimate geographic distribution and prevalence of Ranavirus, chytrid fungus, and helminths in amphibians across the state of North Dakota. I also tested for associations between disease and helminth occurrence and general ecological factors. I sampled broadly across the state, including all major ecoregions and land use categories and obtained a total of 705 amphibians of six different species. I used real time PCR to detect Ranavirus and chytrid fungus infections. I also identified parasites as precisely as possible by morphological and molecular techniques. I found Ranavirus in 238 of 668 (35.6%) assayed amphibians. Ranavirus prevalence varied significantly by species, ecoregion, and land use. Infections were found broadly across North Dakota (55.9%), but exhibited a spatially structured distribution at a finer scale. Ranavirus was more frequently encountered in the Missouri Coteau ecoregion than other ecoregions. I found few occurrence of chytrid fungus (0.007%) and all infections were found in central North Dakota. In contrast, helminths were commonly found. The majority of amphibians were infected with digeneans (60.3%), followed by nematodes (17.4%), but cestodes were much less frequent (2.8%). Parasite species varied intheir distribution across the state, with some showing a fine scale spatial dependency, indicating a patchy distribution. More complete surveys need to be designed to provide a more comprehensive understanding of parasite distributions and ecological associations.
Firkins, Melanie Paige, "Prevalence And Distribution Of Ranavirus, Chytrid Fungus, And Helminths In North Dakota Amphibians" (2015). Theses and Dissertations. 1895.