Polar bear stress hormone cortisol fluctuates with the North Atlantic Oscillation climate index
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Polar bears are heavily dependent on sea ice for hunting sufficient prey to meet their energetic needs. When the bears are left fasting, it may cause a rise in the levels of the stress hormone cortisol. Cortisol is the major corticosteroid hormone in most mammals, including polar bears. Production and regulation of this stress hormone are vital for the body as it is part of a myriad of processes, including in relation to metabolism, growth, development, reproduction, and immune function. In the present study, we examined the correlation between East Greenland polar bear hair cortisol concentration (HCC), a matrix that reflects longer-term hormone levels, and the fluctuations of the North Atlantic Oscillation (NAO) index, a large-scale climate phenomenon applied as a proxy for sea ice extent in the Greenland Sea along the coast of East Greenland. In doing so, a significant positive correlation (r = 0.88; p = 0.0004) was found between polar bear hair cortisol and the NAO, explaining 77 % of the variation in HCC observed between years over the period 1989–2009. This result indicates that interannual fluctuations in climate and ice cover have a substantial influence on longer-term cortisol levels in East Greenland polar bears. Further research into the implications and consequences inherent in this correlation are recommended, preferably across multiple polar bear populations.
KeywordsPolar bear Hair Cortisol Climate NAO Glucocorticoids Stress
Erik W. Born and Aqqalu Rosing-Asvid are acknowledged for collecting the East Greenland polar bear hair samples during the period 1988–1991. Jonas Brønlund and local hunters are acknowledged for organizing the later sampling in East Greenland. Financial support was provided by the Prince Albert II of Monaco Foundation, the Danish Cooperation for Environment in the Arctic, the Commission for Scientific Research in Greenland, the Funds for Scientific Research Flanders, and the University of Antwerp. The hair cortisol assays were supported by US National Institutes of Health Grants RR11122 to MAN and RR00168 to the New England Primate Center.
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