Seasonal Variations of Faecal Cortisol Metabolites in Koalas in South East Queensland

Abstract

The Koala (Phascolarctos cinereus) is an endemic marsupial inhabiting four states of Australia. Urbanisation, declining habitat, drought and fires are threatening the survival of this flagship species. These threats may cause acute and chronic stress in koalas, which might also be associated with occurrence of infectious diseases in koala populations. Stress may induce an increase in cortisol reflected in increased faecal cortisol metabolite (FCM) values. To be able to use faecal cortisol metabolites to measure stress levels in this species, our aim was to determine baseline values for males and females during breeding and non-breeding season. A total of 351 defecations were collected fortnightly, twice a day, for 12 months from koalas at a wildlife facility in South East Queensland. Samples were analysed with three different enzyme immunoassays (EIAs): a cortisol, 5α-pregnane-3β,11β,21-triol-20-one (37e) and tetrahydrocorticosterone (50c) EIA. The latter, which also reacts with tetrahydrocortisol, the main metabolite in koala faeces, was found to have the highest biological sensitivity and, therefore, is the most suitable EIA to measure stress levels in koalas. Utilising this EIA, we found significant differences (p < 0.05) in FCM values between males and females, breeding and non-breeding season, and between morning and evening samples. Values of faecal cortisol metabolites established in stress-free koalas in this study can serve as a reference for future studies in koalas.

Physiological Stress in Rescued Wild Koalas (Phascolarctos cinereus) Being Held in a Rehabilitation Sanctuary: A Pilot Study

“…It is not unusual for male koalas to have been bellowing at the time of data collection in this study, as September to December coincides with the koala breeding season [41]. Previous studies have been able to detect considerable differences between koalas during the breeding season with a rise in glucocorticoids, compared to the non-breeding season [34].…”

“…This means that there is no current glucocorticoid baseline with which to compare the results of this study. A previous study tested different enzyme immunoassays on faecal samples from 13 captive koalas over a 12-month period, which generated some important preliminary baseline data [34]. However, a gap remains for baseline glucocorticoid data for faecal and fur samples in wild koalas.…”

Over Time Decay of Cortisol Metabolites in Faecal Pellets of Koalas in Central Queensland

“…The extraction procedure and analyses are described in Santamaria et al [ 6 ]. In brief, 500 mg of ground samples, neither treated by heat nor freeze-dried, was placed into a 10 mL tube and 5 mL of 80% methanol was added.…”

“…Completely dried down aliquots (0.25 mL) of the extracts in 1 mL Eppendorf tubes, sealed with paraffin film, were shipped to the University of Veterinary Medicine (Austria), where dried sample extracts were resolubilised in 80% methanol and a further dilution step with assay buffer (1 + 9). Aliquots were analysed in duplicate with the cortisol (37e) and tetrahydrocorticosterone (50c) enzyme immunoassays (EIAs), as described in Santamaria et al [ 6 , 9 ].…”

“…Faecal material can be used to measure faecal cortisol metabolite (FCM) values [ 5 , 6 ], which are an indicator of adrenal activity and can be related to physiological responses to stressors [ 2 ]. Currently, the use of fresh faecal samples is recommended for this type of analysis [ 5 , 6 , 7 , 8 , 9 ]. However, freshly defecated pellets are not always available in field studies.…”