Doctoral Dissertations

Date of Award


Degree Type


Degree Name

Doctor of Philosophy


Comparative and Experimental Medicine

Major Professor

Debra Miller

Committee Members

Louise Rollins-Smith, Gary LeCleir, Benjamin Fitzpatrick


The Hellbender (Cryptobranchus alleganiensis), is a large aquatic salamander containing two subspecies, Ozark Hellbender (C. a. bishopi), and Eastern Hellbender (C. a. alleganiensis), from the Ozark mountains and eastern U.S., respectively. Both subspecies have seen population declines over the past 25 years, especially in C. a. bishopi which is federally endangered. Arkansas C. a. bishopi populations have been reduced to a single river with minimal observed juvenile recruitment. Furthermore, over the past decade biologist have observed an increase of distal limb lesions with unknown etiology. We performed yearly surveys of C. a. bishopi in Arkansas and C. a. alleganiensis in Tennessee during summers of 2011-2017, and recorded biometrics, obtained disease samples of a skin swab and tail punch biopsy as well as recorded both qualitative and quantitative details of lesions present. In 2014 we collected an additional dorsal skin swab for skin microbiome analysis. We performed qPCR to test for presence of Batrachochytrium dendrobatidis (Bd) from skin swabs and Ranavirus from tissue. From lesion data we developed a lesion scoring system from 0-7 and applied a lesion score to each hellbender blinded to any other associated information. We performed linear mixed model regressions followed by AICc model evaluation to evaluate effects of pathogen infection status and individual biometrics on lesion score. From our microbiome swabs we performed 16S amplicon sequencing and calculated both Shannon Weiner Diversity and Bray Curtis Dissimilarity scores. We discovered 93.2% of all hellbenders had distal limb lesions characterized by digit swelling often progressing towards toe-tip ulceration. In severe cases we observed digital necrosis progressing to complete digit loss. Any recaptured individuals had the same or worse lesion score with an average score increase of 1 per year. The top predictive model for lesion severity included individual mass and Bd infection status with a significant, albeit weak, positive effect of Bd on lesion severity (β=0.87; C.I.: 0.11, 1.63). Microbiome results revealed decreased skin microbial community stability with increasing lesion score. Results demonstrate lesions are progressive, may be associated with overall skin health, and are likely multifactorial.

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