Faecal glucocorticoid metabolites as a measure of adrenocortical activity in polar bears (Ursus maritimus)

Abstract

Analysis of faecal glucocorticoid metabolites (FGMs) is frequently applied to assess adrenocortical activity in animal conservation and welfare studies. Faecal sample collection is non-invasive and feasible under field conditions. FGM levels are also less prone to circadian rhythms, episodic fluctuations and short acute stressors than glucocorticoid (GC) levels obtained from other matrices, for example blood or saliva. To investigate the suitability of FGM measurement in polar bears (Ursus maritimus), a species listed as Vulnerable by the IUCN (International Union for Conservation of Nature), a cortisol enzyme immunoassay (EIA) was biologically validated by demonstrating a significant increase in FGMs after five zoo-to-zoo transports. In addition to validating the method, the study also documented an average delay of 7 h until the first occurrence of food colorants in the monitored polar bears, which provides essential information for future studies. After validation, the assay was applied to measure FGM concentrations of five polar bears over a 1-year period. Several pre-defined potentially stressful events were recorded in an event log to measure their effect on FGM concentrations. A mixed model analysis revealed significant increases in FGM concentrations after social tension and environmental changes, whereas season and sex had no significant effect. The study demonstrates that the applied cortisol EIA is suitable for measuring FGM levels in polar bears and that using a carefully validated assay for FGM analysis in combination with a detailed sampling protocol can serve as a valuable tool for evaluating mid- to long-term stress in polar bears. FGM levels can be used to monitor stress in captive polar bears in order to optimize housing conditions but also to elucidate stress responses in wild populations for targeted conservation measures.

Methodological Considerations for Using Fecal Glucocorticoid Metabolite Concentrations as an Indicator of Physiological Stress in the Brown Bear (Ursus arctos)

“…Therefore, the assay presented here provides an efficient and modern alternative to measure endocrine stress responses in the brown bear. Interestingly, the cortisol that the EIA identified as the most suitable for brown bears in our results has also been shown as the most suitable for the closely related polar bear (Ursus maritimus; Hein et al 2020).…”

The Adrenal Cortisol Response to Increasing Ambient Temperature in Polar Bears (Ursus maritimus)

“…The only way to determine a sex difference in the metabolism of cortisol would be to do a radio-label infusion in polar bears of both sexes, which has not been done to date. A sex difference in fecal cortisol metabolite concentrations was not observed in a recent study on zoo polar bears using a different polyclonal antibody, but the study included only five bears in total [41]. In contrast, Oskam et al, 2004 [42] found higher serum cortisol in adult females compared to adult males in samples collected from over 200 free-ranging polar bears in Norway.…”

Changes in Fecal Glucocorticoid Metabolites in Captive Coyotes (Canis latrans): Influence of Gender, Time, and Reproductive Status

“…While variability among individuals can reduce distinct patterns of fGCMs, predators, in general, show higher fGCMs during the breeding season than the non-breeding season. For example, female fishing cats ( Prionailurus viverinus ) and wolves exhibited higher fGCMs during winter (breeding season) compared to the non-breeding summer season [ 24 , 26 , 55 ], although no seasonal pattern was observed in polar bears [ 29 ] and tigers [ 6 ], suggesting that body size and/or food requirements may influence fGCM values. Seasonal GCM levels are modulated as a balance between required energy expenditure and available energy [ 1 ], but since the food available to our captive coyotes was constant, our fGCMs levels were likely not influenced by food availability or the demands of producing pups and were likely a stress response to an outside stimulus.…”

“…Examination of GC and GCM levels at a broad temporal scale indicated that there were changes between the breeding and non-breeding seasons [ 1 , 24 , 25 , 26 , 27 ], with most mammalian species exhibiting an increase in GCs and GCMs during the reproductive season, late pregnancy [ 28 ], and lactation. While polar bears ( Ursus arctus ) in zoos did not exhibit seasonal differences [ 29 ], domestic cats ( Felis catus ; [ 30 ]), Amur wildcats ( Prionailurus bengalensis euptilura ; [ 31 ]), and Eurasian lynx ( Lynx lynx ; [ 32 ]) demonstrated a consistent increase in hair cortisol values during the mating season. The caracal ( Caracal caracal ), which is not a seasonal breeder (i.e., can breed any time of the year), exhibited a higher increase in hair cortisol during the autumn and lower during the spring [ 31 ].…”