The effects of age, season, and gender on serum cortisol levels in the tammar wallaby, Macropus eugenii

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

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.

A review of factors influencing the stress response in Australian marsupials

Many Australian marsupials are threatened species. In order to manage in situ and ex situ populations effectively, it is important to understand how marsupials respond to threats. Stress physiology (the study of the response of animals to challenging stimuli), a key approach in conservation physiology, can be used to characterize the physiological response of wildlife to threats. We reviewed the literature on the measurement of glucocorticoids (GCs), endocrine indicators of stress, in order to understand the stress response to conservation-relevant stressors in Australian marsupials and identified 29 studies. These studies employed a range of methods to measure GCs, with faecal glucocorticoid metabolite enzyme immunoassay being the most common method. The main stressors considered in studies of marsupials were capture and handling. To date, the benefits of stress physiology have yet to be harnessed fully in marsupial conservation. Despite a theoretical base dating back to the 1960s, GCs have only been used to understand how 21 of the 142 extant species of Australian marsupial respond to stressors. These studies include merely six of the 60 marsupial species of conservation concern (IUCN Near Threatened to Critically Endangered). Furthermore, the fitness consequences of stress for Australian marsupials are rarely examined. Individual and species differences in the physiological stress response also require further investigation, because significant species-specific variations in GC levels in response to stressors can shed light on why some individuals or species are more vulnerable to stress factors while others appear more resilient. This review summarizes trends, knowledge gaps and future research directions for stress physiology research in Australian marsupial conservation.

Endocrine rhythms in the brown bear (Ursus arctos): Evidence supporting selection for decreased pineal gland size

Many temperate zone animals adapt to seasonal changes by altering their physiology. This is mediated in large part by endocrine signals that encode day length and regulate energy balance and metabolism. The objectives of this study were to determine if the daily patterns of two important hormones, melatonin and cortisol, varied with day length in captive brown bears (Ursus arctos) under anesthetized and nonanesthetized conditions during the active (March-October) and hibernation periods. Melatonin concentrations varied with time of day and season in nonanesthetized female bears despite exceedingly low nocturnal concentrations (1-4 pg/mL) in the active season. In contrast, melatonin concentrations during hibernation were 7.5-fold greater than those during the summer in anesthetized male bears. Functional assessment of the pineal gland revealed a slight but significant reduction in melatonin following nocturnal light application during hibernation, but no response to beta-adrenergic stimulation was detected in either season. Examination of pineal size in two bear species bears combined with a phylogenetically corrected analysis of pineal glands in 47 other species revealed a strong relationship to brain size. However, pineal gland size of both bear species deviated significantly from the expected pattern. Robust daily plasma cortisol rhythms were observed during the active season but not during hibernation. Cortisol was potently suppressed following injection with a synthetic glucocorticoid. The results suggest that melatonin and cortisol both retain their ability to reflect seasonal changes in day length in brown bears. The exceptionally small pineal gland in bears may be the result of direct or indirect selection.

Haematology and serum biochemistry of adult free-ranging mountain brushtail possums (Trichosurus cunninghami), including correlations with season, sex, age, habitat type and disease status

For many wildlife species only limited data are available on haematology and blood biochemistry for free-ranging populations because these are often difficult to obtain. We collected blood samples from wild adult mountain brushtail possums (Trichosurus cunninghami) in the Strathbogie Ranges, Victoria (Australia), over two years, to provide reference values for haematological and some serum biochemical parameters (serum protein, sodium, chloride, potassium, urea, creatinine, creatine kinase and cortisol) for free-ranging animals. We also investigated patterns associated with sex, season, age, habitat type and disease status, including a form of skin disease (rumpwear – one of the major diseases of brushtail possums) and parasite loads. Values for several blood parameters correlated with sex, and most also changed significantly with season. Eosinophil counts increased significantly with the number of strongyle eggs in faeces, and packed cell volume decreased significantly with increasing numbers of ticks. Surprisingly, there was a significant negative relationship between mean population serum cortisol concentrations and the prevalence of rumpwear. Serum sodium and chloride concentrations were significantly lower in possums with moderate to severe rumpwear; however, the biological significance of this is unclear. While there is a growing body of data on the blood parameters of marsupials, these are mainly derived from captive animals, or single sample sets from wild populations, thus are unlikely to accurately reflect the changing status of wild animals/populations across seasons and under varying environmental conditions and parasite loads. More comprehensive, longer-term data from free-ranging marsupial populations, such as those presented here, provide extremely important reference data to aid in determining the health status of wild populations and interpreting data collected from individuals.

Non-invasive assessment of stress in captive numbats, Myrmecobius fasciatus (Mammalia: Marsupialia), using faecal cortisol measurement

Annual patterns of faecal cortisol metabolite (FCM) secretion were examined in six captive numbats (Myrmecobius fasciatus). The use of enzyme-immunoassay for the measurement of FCM in the numbat faeces was validated using an adrenocorticotropic hormone (ACTH) challenge and the resultant FCM measurements represent the first description of adrenal endocrinology in this species. Total overall, baseline and peak FCM mean concentrations varied according to individual, but not gender. For males, mean baseline and overall FCM secretion was higher in spring in summer (compared to winter and autumn) and was elevated during the breeding season. For females, mean baseline FCM secretion did not differ by season or breeding season, but mean overall FCM secretion was elevated during the breeding season. Thus, male (but not female) numbats display an annual change in FCM secretion that is strongly linked to their seasonal pattern of reproduction. Significant FCM elevations (n=178) were observed in response to 20 different stressors, with these stressors being allocated to one of six categories: ANIM, ENVIRO, HAND, HEALTH, MAN and UNK. The mean proportion of positive responses to each category varied according to category, season and breeding season, but did not vary by individual or gender. ANIM and HEALTH stressors elicited a higher response rate than all other categories and an increase in the number of ANIM, ENVIRO, and HEALTH stressors were observed during the breeding season. Although there were multiple stressors within the captive environment that the numbats reacted to, this did not translate into a welfare issue.

Adaptation of wild-caught Tasmanian devils (Sarcophilus harrisii) to captivity: evidence from physical parameters and plasma cortisol concentrations

This study assessed whether capture and transferral into captivity represents a significant stressor to Tasmanian devils. Four male and four female devils were captured in the wild and housed for 6 months in captivity in male–female pairs. Blood samples were collected for cortisol assay at capture, every 24 h for the first 4 days, and then monthly; body weight and tail width were monitored weekly. In the males, mean plasma cortisol concentrations were highest (49 ± 9.19 ng mL–1) at the time of initial capture; cortisol concentrations declined significantly after 48 h in captivity (9.2 ± 5.96 ng mL–1) and did not change significantly over the months in captivity. Females exhibited a different pattern: plasma cortisol concentrations were highest (74.0 ± 3.24 ng mL–1) in the initial sample, but mean concentrations remained elevated in samples taken at 24, 48 and 96 h after initial capture, and did not exhibit a significant decline (to 20.65 ± 8.95 ng mL–1) until 4 weeks after capture. During the first 2 months in captivity, the male devils lost ~8.7% of their original body weight, and females lost 10.6% during this same period. However, body weights then rose during the rest of the experiment. These results suggest that Tasmanian devils experience elevated plasma cortisol concentrations in response to capture and transfer into captivity. However, these high concentrations are not maintained during 6 months in captivity, suggesting that the animals are not chronically stressed.

Are serum cortisol levels a reliable indicator of wellbeing in the tammar wallaby, Macropus eugenii?

Serum corticosteroid levels were measured in six female tammar wallabies (Macropus eugenii) at Macquarie University, NSW, Australia, to assess their reliability as indicators of wellbeing in this species. Animals were challenged with a change in conditions over the course of approximately 3 weeks, comprising (i) isolation and movement; (ii) altered feeding routine, in order to impose a disturbance to homeostasis ("stress"). Blood samples were collected five times during the study period, and analysed for corticosteroid concentration and a number of haematological and biochemical measures. The use of enzyme immunoassay for the measurement of corticosteroids in marsupial serum was validated. We found that there was no significant change in serum corticosteroid concentrations in response to either of the changed conditions suggesting that serum corticosteroid concentrations are not reflective of a change in wellbeing. Cortisol was the dominant serum corticosteroid, with concentrations up to 50 times higher than corticosterone. Significant differences were observed in aspartate amino-transferase, alanine amino-transferase, haemoglobin, total erythrocyte count and mean corpuscular haemoglobin concentration over the period of study. However, no significant correlations emerged to justify any of these measures, or serum corticosteroid levels, as reliable indicators of compromised wellbeing in the tammar wallaby.