Abstract
Simple SummaryKoala habitat is threatened by urbanisation, agricultural activities and by increased temperatures and droughts caused by climate change. Habitat loss may cause stress in koalas, which, in turn, may exacerbate disease occurrence. Stress is associated with an increase of glucocorticoids, of which cortisol is the main one in most mammals. Cortisol is heavily metabolized and excreted via the faeces, where its metabolites can be measured, without interfering with the animal. However, before a link between events causing stress in koalas can be established, baseline levels in stress-free koalas need to be established. Our study has established which diagnostic procedure is best suited to measure these metabolites and has evaluated the physiological baselines levels in male and female koalas and in koalas during the breeding and non-breeding season.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.
Highlights
The Koala (Phascolarctos cinereus) is an endemic marsupial species, whose range spans throughout eastern and south eastern Australia
Overview of faecal cortisol metabolite (FCM) Values Measured by enzyme immunoassays (EIAs)
The box whisker plots indicating the variation of FCM values for each of the 13 koalas, measured with the cortisol, 37e, and 50c EIAs are shown in Figure S1 (Supplementary Materials)
Summary
The Koala (Phascolarctos cinereus) is an endemic marsupial species, whose range spans throughout eastern and south eastern Australia. As many populations are declining, koalas have been listed as vulnerable in Queensland, the Australian Capital Territory and New 4.0/). Due to increased urbanisation along the east coast of Australia, anthropogenic activities, causing fragmentation and loss of habitat, are major threats [2,3,4] to this flagship species [5,6]. Koala populations are increasingly impacted by extensive clearing of habitat due to agriculture activities and mining, as well as droughts exacerbated by climate change [7,8]. Loss of habitat is an important stressor in wildlife often associated with the spread of infectious diseases [9], and this has been documented in koalas [3]
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