Date of Award

2025

Degree Name

Biological Sciences

College

College of Science

Type of Degree

M.S.

Document Type

Thesis

First Advisor

Dr. Jayme Waldron

Second Advisor

Dr. Brian Antonsen

Third Advisor

Dr. Emily Taylor

Fourth Advisor

Dr. Shane Welch

Abstract

Eastern Diamondback Rattlesnakes (Crotalus adamanteus; EDBs) are a declining species endemic to the Southeastern Coastal Plain. Reproduction is costly for females, which are ovoviviparous, slow to mature, reproduce infrequently, and are often emaciated after parturition. Yet, we have a limited understanding of the trade-offs associated with their reproductive biology. Thus, I had three objectives: 1) assess reproduction-associated water stress and determine how female EDBs respond to altered water budgets in situ (Chapter 1), 2) evaluate the interactive effects of body condition and rainfall on female hydration, with a special focus on musculature as a condition index (Chapter 1), 3) characterize differences in blood chemistry parameters associated with reproduction and use circulating solute concentrations to measure hydration state in the absence of an osmometer (Chapter 2), and 4) evaluate predictors of mature female survival probability (Chapter 3). I collected data from an island-dwelling population in South Carolina between 2022–2023. For Chapter 1, I measured plasma osmolality (pOsm, determined via freezing-point depression osmometer) of mature females (n = 41) of known reproductive status (nonreproductive, reproductive [i.e., gestating]). I used an information theoretic approach to explain trends in pOsm associated with rainfall, reproductive status, body size, gestation time, and relative fecundity. Mean plasma osmolality of adult females was 331 mOsm.kg-1 . Results indicated osmoregulation can prove challenging for EDBs despite a subtropical climate, and that females rely on precipitation to osmoregulate; pOsm was negatively associated with precipitation and positively associated with time since rain. Further, pOsm was positively associated with the temporal progression of gestation (n = 15), indicating that gestating females became more vulnerable to osmotic stress as parturition neared. Additionally, females (n = 26) with reduced musculature tended to experience a more lasting hydric benefit from rainfall events. In coming decades, summer droughts are expected to increase in frequency, when hydric demands are likely at their highest for this demographic. Water scarcity emerging with climate change therefore has the potential to further destabilize populations under extreme conditions, and managing freshwater resources may become indicated. For Chapter 2, I compared standard blood chemistry analytes and used levels of sodium, potassium, glucose, blood-urea-nitrogen, and uric acid to calculate pOsm (calculated plasma osmolality; pOsmc). I used Bland-Altman plots to determine levels of agreement between measured pOsm (pOsmm, determined via osmometer) and pOsmc. Further, I compared EDB pOsmm with those of other squamates. Reproductive females slightly higher chloride (n = 22) and lower cholesterol (n = 19) levels than nonreproductive snakes, and the equation 2([Na+ + K+ ]) + (Glu/18) was effective for calculating plasma osmolality (n = 22), baselines for which appear species-specific. Results from this work offer the first published description of EDB blood chemistry parameters and provide an equation for pOsmc, potentially benefitting further research into EDB hydration or provision of medical care in captive settings. Findings also suggested that plasma osmolality is a useful measure of hydration state regardless of reproductive status. For Chapter 3, I used a known fate framework in program MARK to quantify annual survival of telemetered females (n = 23) with respect to dormant season body condition, reproductive status, relative fecundity, season, and ordinal severity scores reflective of grossly apparent lesions consistent with ophidiomycosis (caused by the pathogen Ophidiomyces ophidiicola; Oo). Mature female survival was negatively associated with lesion severity and dormant season body condition. The survival estimate for this subset was the lowest on record (i.e., 68%), suggesting that ophidiomycosis poses a critical health threat to EDBs and that additional research to understand and mitigate this threat is urgently needed.

Subject(s)

Wildlife conservation.

Eastern diamondback rattlesnake.

Biology.

Ecology.

Eastern diamondback rattlesnake -- Reproduction.

Eastern diamondback rattlesnake -- Fertility.

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