Pilot study investigating the role of corticosterone binding globulin as an indicator of endocrine stress response in marine mammals

Sibel Karchner, Neel Aluru and Andrea Bogomolni Biology

Abstract

Anthropogenic activities are causing extensive damage to the marine ecosystems. The long-term
consequences of these activities on the environment and marine biodiversity are not well characterized. Marine mammals are one of the major groups of aquatic animals that are shown to be vulnerable to anthropogenic stressors. So far most of our understanding on the impact of stressors comes from lethal effects such as by catch, strandings and vessel collisions. Very little is known about the non-lethal effects of anthropogenic stressors. In response to stress, marine mammals elicit a highly conserved physiological stress response by activating the brain-pituitary-adrenal axis, leading to elevated cortisol levels. Cortisol, a glucocorticoid hormone, induces physiological and behavioral changes necessary for coping with stress. Elevated cortisol levels are
used as an indicator of exposure to acute stressors. Cortisol that is released into the circulation is bound to a transport protein, termed corticosterone binding globulin (CBG) and carried to the target tissues. The biologically active component is the free (unbound) cortisol and CBG-bound fraction is considered to be the storage form of hormone that will be utilized on chronic or repeated exposure to stressors.
Hence, CBG levels act as a buffer and are considered to be an important indicator of chronic stress in mammals. However, the impacts of prolonged or chronic exposure to stress or the CBG levels in marine mammals are not known. Hence, the objective of this pilot study is to standardize the methods for detection of CBG levels and to establish its reliability as an indicator of stress in marine mammals. Studying marine mammals presents unique challenges because they cannot be easily captured or sampled for blood using traditional methods. In this collaborative study, we are utilizing the seal samples collected from natural populations and from local aquariums to establish this method. As seals are considered the sentinels on marine ecosystem health, the results from this project will provide important information on the health status of these animals. Once the method for detection of CBG has been validated, this method can be easily applied to other species of marine mammals.