Environmental Influences on Amphibian Innate Immune Defense Traits Disease-associated mortality is a leading cause of amphibian declines world-wide; therefore, understanding the influence anthropogenic environmental change has on traits which provide disease resistance is important for successful amphibian conservation. Amphibians are protected from pathogens by two skin-associated immune defense traits: the microbial communities which inhabit their skin (microbiome) and the antimicrobial peptides (AMPs) produced by the skin. Utilizing experimental and observational studies, I investigated the relationships between the environment and amphibian skin-associated immune defense traits. I found that small pH shifts (i.e. from ̃7 to 6) in the larval environment caused changes in Rana catesbeiana larval microbiome structure, an effect which disappeared after metamorphosis. Additionally, I found post-metamorphic AMP production and bioactivity were significantly affected by interactions between population, pH, and the presence or absence of shade in the larval environment. In an observational field survey I found that Acris blanchardi populations across Ohio and Michigan differed in microbiomes and AMP production, but not AMP bioactivity against Bd (Batrachochytrium dendrobatidis). Microbiomes were associated with water conductivity, ratio of natural to managed land, and latitude. Additionally the microbiomes were affected by interactions between frog sex and latitude, between frog sex and water surface area, and between the ratio of natural to managed land and water surface area. AMP production was influenced by the interaction between water surface12area and conductivity. Finally, I examined the influence of a glyphosate-based herbicide on A. blanchardi skin-associated immune defense traits across life stages and at differing, environmentally relevant concentrations. I found a 37% decrease in survival of larvae exposed to 2.5mg/L of active ingredient (glyphosate) compared to control, but no effects on juvenile survival. Larval herbicide concentration did alter the larval microbiome, but did not alter larval duration and did not carryover to alter post-metamorphic traits. Furthermore, herbicide concentration only marginally affected juvenile mass and the juvenile microbiome. I did not find evidence of effects of the host's AMPs affecting the skin microbiome in any of my studies, indicating that the environment external to the amphibian is relatively more influential on the amphibian skin-associated microbiome compared to this physiological trait of the host. |
