Dangerous Waters? Environmental Effects on Dolphin Immune and Endocrine Health

In a recent PLoS One study, researchers observed an upregulation of immune system function in wild dolphins compared with managed-care dolphins, illustrating the environment’s effect on dolphin immune and endocrine responses.

Wild marine mammals mount pathophysiologic responses to the many natural and anthropogenic stressors in their environment. However, very little is known about these responses, leaving large knowledge gaps about marine mammals’ stress responses and immune systems. In addition, across species, few studies have compared immune responses between wild animals and their managed-care conspecifics.

Anthropogenic environmental stressors, such as persistent organic contaminants, are particularly problematic for marine mammals. Previous studies have reported immunosuppression with polychlorinated biphenyl; interestingly, poly- and perfluoroalkyl substances have been shown to upregulate immune function in Charleston dolphins.

Study Details

Over 1 to 2 years, researchers collected blood samples from 2 groups of managed-care dolphins and 2 wild dolphin populations.

Managed-Care

• Georgia Aquarium (GA): controlled indoor environment
• U.S. Navy Marine Mammal Program (MMP), San Diego Bay: open-water, netted enclosures

Wild

• Indian River Lagoon (IRL), Florida
• Charleston, South Carolina (CHS)

Multiple samples were collected from the managed-care dolphins and single samples were collected from the wild dolphins. Researchers used the samples to analyze a wide range of markers of immune and endocrine function.

Hematology

Levels of many of the hematologic parameters, including eosinophil, lymphocyte, and platelet concentrations, were significantly lower in the managed-care than wild dolphins. Notably, eosinophil concentrations were lowest in the GA dolphins. When comparing the wild populations, most observed differences in hematologic parameters were not significant.

Serum Proteins

Total protein concentration was significantly lower in the managed-care than in wild dolphins. In particular, the lower concentrations of total acute phase proteins in the managed-care dolphins likely reflected reduced foreign pathogen exposure and a lack of acute systemic inflammation in a managed-care setting, the researchers noted.

Hormones

Thyroid hormone levels were highly variable between groups, demonstrating no clear pattern. This suggested a possible effect of other environmental factors, such as water temperature, on thyroid metabolism in dolphins, the researchers wrote.

Adrenocorticotropic hormone (ACTH) levels were highest in IRL dolphins. In addition, epinephrine concentrations were highest in the wild dolphins. Researchers recommended cautious interpretation of results for ACTH and other stress-related parameters, though, because capture itself causes stress in wild dolphins.

Immune Parameters

Numerous immune parameters were significantly different between managed-care and wild dolphins. For example, IgG concentrations were lowest in GA dolphins, indicating low antigen and pathogen exposure. Also, antibody titers to several bacteria were generally higher in wild dolphins than managed-care dolphins, reflecting increased exposure to infectious agents.

Differences in cytokine expression, especially that of IL-4, were notable; IL-4 is associated with IgE production and helminth elimination. IL-4 expression levels were higher in MMP, IRL, and CHS dolphins than GA dolphins. This was expected, researchers noted, because MMP and wild dolphins live in natural seawater environments, increasing their helminth exposure.

Conclusions

Although study results indicate the environment’s influence on immune and endocrine responses in dolphins, it is unknown whether the observed differences in responses between the managed-care and wild dolphins were biologically or clinically significant. Researchers recommended further analysis to better understand the differences in basic immune function between managed-care and wild animals, as well as the interaction between the immune and endocrine systems in dolphins.

Dr. JoAnna Pendergrass received her Doctor of Veterinary Medicine degree from the Virginia-Maryland College of Veterinary Medicine. Following veterinary school, she completed a postdoctoral fellowship at Emory University’s Yerkes National Primate Research Center. Dr. Pendergrass is the founder and owner of JPen Communications, a medical communications company.