The Consequences of Long-term Stress in Bottlenose Dolphins (<i>Tursiops truncatus</i>)

Long-term stress can produce physiological effects that impact survival and reproduction. Identifying stress-induced physiological responses and quantifying their costs is important to the development of predictive models of how repetitive or long-term anthropogenic stressors impact marine mammals at the individual and population level. The most conserved response to a stressor in vertebrates is an increased production of cortisol (or corticosterone). To assess the cost of a long-term stress response in a representative odontocete, we simulated exposure to a continuous stressor by elevating circulating cortisol in five bottlenose dolphins over a seven-day period. The physiological response to the stressor and its associated cost was measured with respect to changes in metabolic hormones, immune function, metabolic rate, and body composition. Circulating cortisol levels were elevated by feeding 60 mg of hydrocortisone in a fish to the dolphins at six-hour intervals over the course of a week. Oxygen consumption was measured using open-flow respirometry in each dolphin three times over the week preceding the hydrocortisone treatment, and three times over the week of the treatment. Voluntary blood samples were collected after each respirometry session to assess metabolic hormones (e.g., triiodothyronine (T3), dehydroepiandrosterone, adiponectin) and immunochemistry (e.g., IgG, IgE). Body composition, assessed with the deuterium dilution method, was determined in each dolphin at the end of the baseline sampling week and treatment week. Preliminary results suggest that sustained elevated cortisol levels induce metabolic suppression, but individual variability exists. The suppression is consistent with observations of a prior study in which free T3, the primary hormone regulating metabolism, decreased when cortisol was elevated in dolphins over a week. Quantification of changes in metabolic hormones will provide additional insight into physiological changes induced by chronically elevated cortisol. Results should better inform predictive models of the cost of disturbance and stress in small odontocetes. Office of Naval Research This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.