Graduate Thesis Or Dissertation

 

The Effects of Nitrate and a Pathogenic Fungus, Batrachochytrium dendrobatidis, on Amphibians Public Deposited

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  • The current rate of global biodiversity loss and extinctions is unparalleled and a major concern. Freshwater organisms are facing particularly rapid rates of biodiversity loss. Amphibians, which require an aquatic environment for part of their life cycle, are one of the most vulnerable vertebrate groups. Amphibians are experiencing population declines, range reductions and a number of extinctions worldwide and between 30 to 40 percent of amphibian species are threatened with extinction. No single cause is accountable for all amphibian population losses though these causes include habitat destruction, environmental contaminants, invasive species, climate change and disease. Emerging infectious diseases have gained attention due to their increasing prevalence in wildlife, including amphibians. One pathogen, the fungus Batrachochytrium dendrobatidis (Bd) that causes chytridiomycosis, has been associated with amphibian mortality events and some population declines. Amphibian host response varies widely to Bd and can depend on species, population, life stage and pathogen strain. Though a variety of factors may influence this range in host response, one hypothesis is that other stressors may increase host susceptibility to the disease. To explore the hypothesis that pollutants can exacerbate the effects of chytridiomycosis, I investigated whether a ubiquitous environmental contaminant, nitrate, can increase mortality when larval amphibians are exposed to Bd. I used a 3 x 2 experimental factorial design to expose two amphibian host species, the Pacific treefrog (Pseudacris regilla) and the Cascades frog (Rana cascadae) to three levels of nitrate (no nitrate, low, or high) and two levels of Bd (absent or present). Nitrate alone and Bd alone did not significantly affect mortality in either species. However, the high nitrate treatment in combination with Bd significantly reduced survival in P. regilla, and treatments with both high and low nitrate and Bd significantly reduced survival in R. cascadae. The treatments with nitrate and/or Bd increased growth and development for both species in comparison to the control treatments overall. This research provides evidence to support the hypothesis that contaminants may increase the severity of chytridiomycosis and induce other sublethal effects. My results show that sublethal levels of two environmentally relevant stressors can increase mortality in amphibians when in combination. Because nitrate is a pervasive contaminant that amphibians commonly encounter in water, the importance of understanding how nitrate contamination can affect amphibians cannot be overstated. Identifying contaminants that may increase mortality when in the presence of a pathogen is a crucial step toward understanding how to manage amphibian populations at risk of declining.
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  • 2017-08-16 to 2018-08-09

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