Theses and Dissertations

Date of Award

8-2025

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Ocean, Coastal, and Earth Sciences

First Advisor

Roldán Valverde

Second Advisor

MD Saydur Rahman

Third Advisor

Richard Kline

Abstract

Sea turtles exhibit distinct behaviors before and after egg laying, however, not all individuals successfully oviposit. Some females display disruptions in their typical nesting behavior, returning to the water without laying eggs, which is referred to as a non-nesting emergence (NNE). NNEs can be due to external disturbances on the beach, but why they occur is often unclear. Arginine vasotocin (AVT) is a neuropeptide involved in various physiological processes, including stimulating smooth muscle contraction of the oviduct to facilitate egg deposition in nesting sea turtles. On the other hand, corticosterone is the primary stress hormone in sea turtles and is frequently measured to study the endocrine stress response of these reptiles. To better understand these NNEs from a physiological standpoint, we tested the hypotheses that: (1) NNEs occur due to the failure of circulating AVT to rise sufficiently to undergo egg laying, and that (2) elevated corticosterone is responsible for inhibiting the rise in AVT. To address these hypotheses, I collected blood samples from nesting loggerhead turtles exhibiting NNEs (n=5) and the normal egg laying process (n=27) at the X’cacel-X’cacelito sanctuary in Quintana Roo, Mexico. The mean AVT concentration measured in NNE individuals after aborting nest construction was similar to the concentration of a female that had begun to lay eggs (n=1). Although it remains unclear whether the nesting process was aborted due to an insufficient rise in AVT, the findings raise the possibility that a threshold for AVT may be required for the transition from nest construction to oviposition. On the other hand, mean corticosterone concentration was similar across the entire nesting effort of successful nesters and those exhibiting NNEs, consistent with concentrations reported for non-stressed sea turtles. Thus, corticosterone did not seem to influence AVT secretion and appeared to play no role in the occurrence of NNEs. While my findings suggest that corticosterone is not a mechanistic factor in NNEs, the physiological relationship between nesting and non-nesting behaviors and AVT remains unclear, warranting further investigation.

Comments

Copyright 2025 Krista Blair Reed. All Rights Reserved. https://proquest.com/docview/3253949353

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