Cortisol levels in hair of East Greenland polar bears

Abstract

To demonstrate the ability to assess long-term hypothalamic-pituitary-adrenocortical (HPA) axis activity in polar bears (Ursus maritimus), a pilot study was conducted in which cortisol concentrations was analyzed in hair from 7 female (3-19 years) and 10 male (6-19 years) East Greenland polar bears sampled in 1994-2006. The hair was chosen as matrix as it is non-invasive, seasonally harmonized, and has been validated as an index of long-term changes in cortisol levels. The samples were categorized according to contamination: eight were clean (2 females, 6 males), 5 had been contaminated with bear blood (2 F, 3 M), and 4 with bear fat (3 F, 1 M). There was no significant difference in cortisol concentration between the three categories after external contamination was removed. However, contaminated hair samples should be cleaned before cortisol determination. Average hair cortisol concentration was 8.90 pg/mg (range: 5.5 to 16.4 pg/mg). There was no significant correlation between cortisol concentration and age (p=0.81) or sampling year (p=0.11). However, females had higher mean cortisol concentration than males (females mean: 11.0 pg/mg, males: 7.3 pg/mg; p=0.01). The study showed that polar bear hair contains measurable amounts of cortisol and that cortisol in hair may be used in studies of long-term stress in polar bears.

Figure 1

Hair cortisol concentration (pg cortisol/mg hair) vs. year of kill for East Greenland polar bears (Ursus maritimus) collected 1994–2006. p = 0.11, r = −0.41 (excl. outlier; year of kill: 1995. 19.9 pg cortisol/mg hair, see text for further explanation). +: female, o: male.

Figure 2

Box-and-whisker plot of hair cortisol concentration (pg cortisol/mg hair) in female and male East Greenland polar bears (Ursus maritimus) (excl. outlier. See text for further explanation). Females had significantly higher mean cortisol concentration in hair than males (p = 0.01).