Measuring glucocorticoids resp. their metabolites in hair and faeces of polar bears (Ursus maritimus)

Background

Measuring glucocorticoids (GCs) is a common and useful method to evaluate an individual’s physical condition referring to stress: whereas the rapid and momentary release of GCs from the adrenal glands during stressful situations denotes a physiological process in healthy individuals, chronically elevated GC levels entail severe damages for the organisms health (e.g. reduced fitness, reproduction disorders, immunosuppression).

In the field of zoo and wildlife medicine especially non-invasive methods for measuring GCs are being used, like the analysis of faecal glucocorticoid metabolites (FGM) or the recently investigated measurement of hair cortisol concentrations (HCC).

As demonstrated in previous studies (Macbeth et al. 2012; Bechshøft et al. 2011, 2012; Shepherson et al. 2013) the analysis of GCs is also possible in polar bear hair and faeces.

However, GC values in these studies differ widely what among others could be attributed to differences of the particular applied laboratory method (sample preparation, extraction, assay etc.).

Furthermore the interpretation of the GC levels obtained from polar bear hair or faeces remains very difficult because no species-specific base lines have been established for polar bears, also relations between stressful events and faecal/hair GCs of polar bears are only insufficiently known. Especially for the evaluation of data from free-ranging polar bears a deeper knowledge of these contexts is needed.

That for, during this study methods of measuring HCCs and FGMs in polar bears will be analytically and biologically validated to establish repeatable and accurate techniques for the analysis of GCs.

Additionally, the investigation of long-term cortisol profiles of zoo polar bears will help to understand seasonal variations in the release of GCs and enable to approach reference values for this species.

Methods

Analytical validation of the assays will be conducted through repeated measurements of opportunistically obtained hair and faecal samples of polar bears in European Zoos according to laboratory standards (specificity, linearity, accuracy, limit of determination/detection).

To biologically validate the measurement of FGMs, feceal samples will be collected in the context of transports (resp. other stressful events), when an increase of GCs can be expected.

For setting up long-term cortisol profiles, hair samples of polar bears from European institutions will be collected for at least 12 months and analysed for cortisol. Hair will be sampled through repeated shavings of the same body region. For the interpretation and biological validation of the measured HCCs possible stressful events (e.g. fights, mating, changes of enclosure) will be recorded by the keepers parallel to the hair sampling.

Summary

By comparing and validating different laboratory protocols for measuring GCs in hair and faeces of polar bears repeatable analysing methods will be established.

Setting up long-term cortisol profiles for captive polar bears will help to approach reference values for these animals. Also, the determination of individual-specific base lines is helpful for the interpretation of GC values.

Thus the investigation of cortisol base lines and circannual fluctuations in captive polar bears is essential for the interpretation and understanding of cortisol levels from wild bears, since a validation and establishment of reference values is hardly possible under field conditions.

With the help of data obtained from captive bears, free-ranging individuals could be specifically monitored and the effect of the loss of sea ice, respectively the influence of nutritional and environmental stress on the population size, investigated.

Cooperation partners

Prof. Dr. Alex Greenwood,
Biologist and Professor of Wildlife Diseases at
Department of Veterinary Medicine, Free University Berlin,
Head of Department of Wildlife Diseases at the Leibniz Institute for Zoo and Wildlife Research (IZW)

Thea Bechshøft, Biologist, MSc, PhD,
University of Alberta, Edmonton, Alberta

Prof. Dr. Clemens Kirschbaum,
Psychologist and Head of
Department of Biopsychology,
Dresden University of Technology;

Prof. Dr. Rupert Palme,
Unit of Physiology, Pathophysiology and Experimental Endocrinology,
Department of Biomedical Sciences,
University of Veterinary Medicine Vienna;

Dr. Katrin Baumgartner,
Zoo and Wildlife Veterinarian,
Zoo Nuremburg;

Dr. Lorenzo von Fersen,
Biologist and Curator for Research & Conservation of
Zoo Nuremberg;