Blubber Hormones: A Marker of Dolphin Health and Well-being
Principal Investigator: Ned Place
Co-PI: Holger Klinck
DESCRIPTION (provided by applicant):
Marine mammals are exposed to a wide range of stressors that originate from both natural and anthropogenic sources. Understanding the impact of stressors on marine mammal health warrants increased attention, but the paucity of available information can limit the conservation efforts of marine resource managers1,2. The stress response in marine mammals is physiologically similar to that of terrestrial mammals. The hypothalamicpituitary-adrenal (HPA) axis is a key component of the stress response and when chronically stimulated, the corresponding impacts could be detrimental to immune health, reproductive success, and survival3,4. Measurements of cortisol, a stress hormone produced by the adrenal gland, are commonly used to assess health and well-being in wildlife5–7. To explore the impacts of chronic stress, we propose to examine blubber cortisol levels in bottlenose dolphins (Tursiops truncatus) that have fatally beach-stranded along the Virginia coastline during the summer months of 2012-2017. The western Atlantic Ocean along Virginia’s coast is an anthropogenically heavily used marine area that experiences frequent and prolonged ‘waves’ of unusual mortality events (UME). Fatal beach stranding is a prolonged and highly physiologically stressful experience and is compounded by local environmental pressures. Thus, these characteristics serve as a marker for chronic stress and should describe the upper reference limit for cortisol8. Summer is generally a high stranding season, and UME’s are characterized by periods of statistically extraordinary strandings and demonstrate general pathologic findings with diagnostics that are consistently found in chronically stressed individuals. To determine the upper range for cortisol levels in blubber, our study will measure cortisol concentrations during relatively high and low stressful environmental conditions, i.e., during UME and non-UME periods. To control for potentially confounding variables, such as season and reproductive state, blubber samples will have been collected during the summer months, which will enable us to evaluate the impacts of stress and cortisol on the levels of progesterone and testosterone in blubber from sexually mature and immature male and female dolphins. The adult vs. juvenile comparisons will also provide additional biological validations for the determinations of sex hormone concentrations in blubber. Blubber tissues were collected between 2012 and 2017 under federal permit by the Virginia Aquarium & Marine Science Center (VAMSC), which has archived these samples and the corresponding necropsy reports and made them available to us for analysis. We will use techniques previously validated in other species of dolphins8, and use appropriate statistical methods to elucidate the differences among defined cohorts of bottlenose dolphins. During this process, a veterinary trainee, Lauren Jacobsen, will gain hands-on experience in state-of-the-art techniques for the analysis of hormones in blubber. The outcome of this study will yield data that can be directly applied to the study of free-living bottlenose dolphins and can function as a low-risk proxy for other delphinid species that are threatened or endangered.