Date of Award


Document Type

Open Access Thesis

Degree Name

Master of Science (MS)



First Advisor

Douglas C. Woodhams

Second Advisor

Micheal Shiaris

Third Advisor

Brook T. Moyers


The repertoire of defenses a host may use against a pathogen is often thought of in the context of innate and adaptive immunity. However, the role of host symbionts such as the microbiome are being examined potentially as part of an individual’s defense against disease. Chytridiomycosis, caused by the fungal pathogens Batrachochytrium dendrobatidis (Bd) and Batrachochytrium salamandrivorans (Bsal), is characterized by an infection of the skin often leading to osmotic imbalance and mortality, and has resulted in losses in global amphibian biodiversity. Understanding what may influence the development of resistance to or tolerance of infection is critical to developing prevention measures and understanding risks to populations. The impact of Bsal re-exposure was tested on Eastern Newts, Notophthalmus viridescens, at the terrestrial juvenile (eft) and aquatic adult life stages. Efts were not very susceptible to infection (22.5% infected) at a moderate temperature (17.5 ℃), and were able to maintain infection with little mortality (85% overall infection prevalence, 13.79% mortality in re-exposed newts, 16.67% mortality in newts exposed in only the second exposure) at the thermal optima for Bsal (14 ℃). No differences in infection load nor the skin microbiome were seen between infected individuals with different exposure histories. Conversely, adult N. viridescens were susceptible at a moderate temperature (17.5 ℃), had less mortality following re-exposure, and harbored different cutaneous communities compared to those only exposed once or naïve to disease. Metrics of diversity were dynamic through time, and also followed different trajectories through time depending on exposure history and survival outcome. These data point towards different responses to Bsal across life stages and likely between populations, but in adults the microbiome may be responsive to disease. In light of susceptibility trials of juvenile newts from another population also tested at 14 ℃ observed much higher mortality, and these data may indicate that Massachusetts populations may be more robust than others. Country and continent-wide risk assessments should account for intra-species variation in susceptibility when identifying the most at-risk spaces. Further, understanding the nature of these responses may be critical for developing preventative or therapeutic probiotic treatments to protect existing biodiversity.

Available for download on Friday, May 31, 2024

Included in

Biology Commons