Consequences of Environmental Alterations on the Gut Microbial Communities of Rana berlandieri Tadpoles




Villatoro Castañeda, Melissa

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The gut microbiome plays an important role in digestion, energy mediation, host fitness, and defense against pathogens, indicating that host health can be assessed through the gut microbiome. Amphibians and their microbiome are highly susceptible to environmental contaminants. Glyphosate, the most widely used herbicide in the United States, is toxic for amphibian larvae and studies suggest that this herbicide also modifies their skin microbiome. This herbicide component can be found in commercially used herbicides such as Roundup®. I explored the gut microbial composition of Rana berlandieri tadpoles and water samples exposed to a non-lethal concentration of Roundup ® Ready-to-use weed & grass killer III (0.74 mg a.e./L of glyphosate) compared to an unexposed control group. Because there were differences in gut microbial communities, dorsal body area, and tail depth between both groups, but no differences in baseline corticosterone (a stress hormone) release rates; I further explored the role of a healthy gut microbiome in anuran larvae fitness and phenotype by comparing tadpoles in a control group to tadpoles exposed to: (1) an environmentally relevant, but non-lethal, glyphosate concentration in Roundup Ready-to-use weed & grass killer III ™ (1.47 mg a.e/L), (2) an antibiotic cocktail to disrupt the natural microbiome of the tadpoles, (3) and a combination treatment of both glyphosate and antibiotics. There were differences in dorsal body area, activity, and gut microbial community composition across all treatments. Specifically, antibiotic and combination exposed tadpoles had the smallest dorsal body area and were the least active; and glyphosate exposed tadpoles were less active than control tadpoles. However, there were no significant differences between antibiotic and combination exposed tadpoles at any measurement level, suggesting that antibiotic alone is enough to suppress growth, change behavior and change the gut microbiome composition. I hypothesize that the changes observed in glyphosate exposed tadpoles, are due the differences in gut microbiome composition and presence of pathogenic bacteria in this group, or the host response to Roundup ® Ready-to-use weed & grass killer III composition. My results suggest that there is a link between a disturbed microbiome and the host phenotype and fitness during tadpole development, further highlighting the importance of a healthy microbiome in anuran development.



glyphosate, amphibians, gut microbiome, tadpole, pollutants


Villatoro Castañeda, M. (2021). Consequences of Environmental Alterations on the Gut Microbial Communities of Rana berlandieri Tadpoles (Unpublished thesis). Texas State University, San Marcos, Texas.


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