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Date of Award
Spring 2025
Rights
Access restricted for 1 year to EWU users with an active EWU NetID
Date Available to Non-EWU Users
2026-06-12
Document Type
Thesis: EWU Only
Degree Name
Master of Science (MS) in Biology
Department
Biology
Abstract
Global climate change and infectious diseases are considered a leading cause of amphibian population declines worldwide. Changes in precipitation and salinity have altered watershed systems and microbial communities, reducing habitat availability and physiological performances for amphibian survival. The salt refuge hypothesis, however, is a proposed explanation that higher saline environments may reduce susceptibility to pathogens such as Batrachochytrium dendrobatidis (Bd). The Moro Cojo Slough State Marine Reserve (MCSSMR) (California, USA) is known as an abundant breeding ground for endangered/threatened amphibian species. To test and expand the salt refuge hypothesis, I evaluated Bd prevalence and intensity and the cutaneous microbiome of the common Pacific Tree Frog (Pseudacris regilla) across a salinity gradient (0.05-30 ppt) at 10 sites within the reserve. I hypothesized that amphibians in higher saline environments would have lower Bd infection rates and different microbial communities compared to freshwater sites and their environment. Fifteen skin swab samples were collected per site and DNA was extracted for the molecular quantification of Bd via qPCR and bacterial community analysis using 16s rRNA gene (V4-V5 region) sequencing. Bd prevalence decreased across our salinity gradient, from 93% in freshwater to 0% in saltwater sites. Infection intensity was significantly lower in low and medium salt groups compared to freshwater. Salinity as a categorical variable was a significant driver of bacterial composition and diversity in both frog and environmental samples. Salinity as a continuous variable was negatively correlated with bacterial alpha diversity in frogs, while the environmental microbial communities remained consistent across the salinity gradient. Lastly, Bd presence and intensity were correlated with skin microbiome structure, although salinity was a stronger driver. These results support the salt refuge hypothesis and indicate the potential for increased habitat restoration projects where changing environmental conditions, like increasing salinity, could limit pathogen infection and improve amphibian conservation efforts.
Creative Commons License
This work is licensed under a Creative Commons Attribution-NonCommercial-No Derivative Works 4.0 International License.
Recommended Citation
Kim, Hannah Eunhae, "The effects of salinity on the cutaneous microbiome and pathogen infection on the Pacific Tree frog (Pseudacris regilla) in Monterey Bay, California, USA" (2025). EWU Masters Thesis Collection. 967.
https://dc.ewu.edu/theses/967
