BEYOND CORTISOL: INDICATORS OF STRESS AND NEGATIVE FEEDBACK IN PLASMA AND BLUBBER OF MARINE MAMMALS

Author

Jessica Avalos, University of the PacificFollow

Date of Award

2022

Document Type

Thesis

Degree Name

Master of Science (M.S.)

Department

Biological Sciences

First Advisor

Jane I. Khudyakov

First Committee Member

Craig Vierra

Second Committee Member

Zachary Stahlschmidt

Abstract

Marine mammals play an important role in ecosystem stability. However, anthropogenic activity is compounding pressure on many already vulnerable populations. A potential consequence of anthropogenic disturbance is physiological stress, which can impact metabolism, immunity, and reproduction, especially if it occurs repeatedly. Previous studies on marine mammals have focused on acute stress, but the impacts of repeated stress are poorly understood. Due to its accessibility on land during haul-outs, the northern elephant seal (Mirounga angustirostris) is a good system in which to study the effects of stress in marine mammals. Stress stimulates the release of glucocorticoid hormones, primarily cortisol. Elevated cortisol is a good indicator of acute stress, but it is an unreliable proxy for chronic stress, and cortisol measurements alone do not provide information on the downstream physiological consequences of chronic stress. Therefore, additional biomarkers may provide a more comprehensive understanding of the effects of repeated stress on marine mammals. I examined two approaches for assessing stress in response to administration of the hormone that stimulates secretion of cortisol (adrenocorticotropic hormone; ACTH): a non-targeted proteomics approach using blood plasma and a targeted gene expression approach examining blubber expression of glucocorticoid receptor (GR) and two of its regulators, FKBP5 and KLF9. For the first approach, I used the highly sensitive LC-MS/MS technique to detect changes in circulating plasma proteins in juvenile seals in response to repeated ACTH administration. I identified changes in relative abundance of proteins of interest in the plasma proteome that included those with roles in lipid, iron, and redox homeostasis, cortisol and thyroid hormone transport, adipogenesis, oxidative stress, blood pressure regulation, vitamin and mineral transport, and innate immunity. I then measured blubber expression of GR and its regulator genes in blubber of adult female seals undergoing early and late molting to examine changes during different life-history stages in response to acute stress induced by ACTH administration. Using RT-qPCR, I found that GR expression decreased in blubber, while expression of FKBP5 increased, suggesting negative feedback at the tissue level which may reduce sensitivity to cortisol during key life-history stages, such as molting, which require fasting. These data provide insights into the resilience of marine mammals to acute stress and novel biomarkers that may be used to study the effects of prolonged stress in wildlife.

Pages

75

Recommended Citation

Avalos, Jessica. (2022). BEYOND CORTISOL: INDICATORS OF STRESS AND NEGATIVE FEEDBACK IN PLASMA AND BLUBBER OF MARINE MAMMALS. University of the Pacific, Thesis. https://scholarlycommons.pacific.edu/uop_etds/3817