Stress Physiology of Bears: Cortisol Dynamics and Identification of Novel Serum Proteins

• Main Author: Chow, Brian Andrew
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: University of Waterloo 2013
• Subjects: stress; bears; proteomics; conservation; cortisol; corticosteroid-binding globulin; Biology; polar bear
• Online Access: http://hdl.handle.net/10012/7406

There is a need to understand how free-ranging animals respond and adapt to stress. However, little is currently known regarding the physiologic adaptations to stress in bears, and there are few tools available to wildlife managers to assess the health and stress status of free-ranging animals, including ursids. The hypothalamus-pituitary-adrenal (HPA) axis plays major roles in the physiological adaptation to stress, leading to the increased secretion of glucocorticoids (e.g. cortisol in most mammals) that mediate adaptive changes in physiology and behaviour. The vast majority of glucocorticoids are bound to its primary carrier protein, corticosteroid-binding globulin (CBG), in most animals, and only the unbound fraction is bioavailable. Thus, CBG plays a major role in modulating glucocorticoid dynamics, and this protein must be characterized to build a more complete understanding of the adaptive role that the HPA axis plays in mitigating stress in bears. The overall objective of this thesis was to characterize the HPA axis activity and CBG levels in bears, and develop tools targeted towards the monitoring of the health and stress status of American black bear (Ursus americanus), grizzly bear (U. arctos), and polar bear (U. maritimus). The binding characteristics of cortisol to CBG in bears were studied via saturation binding experiments, and this information was used to estimate free cortisol concentrations based on CBG concentrations. To quantify CBG concentrations in bears, an enzyme-linked immunosorbent assay (ELISA) was developed. Grizzly bear CBG cDNA was cloned and sequenced, and an antibody was developed against a peptide sequence of the deduced amino acid sequence. The antibody showed good cross-reactivity against black, grizzly, and polar bear CBG, and the ELISA based on this antibody found differences in the mean CBG levels between species. Using this data, free cortisol levels were estimated, and mean levels were elevated in polar bears relative to black and grizzly bears. Having developed these ...