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Non-invasive evaluation of physiological stress in an iconic Australian marsupial: the koala (Phascolarctos cinereus)

Narayan, EJ, Webster, K, Nicolson, V, Mucci, A & Hero, J 2013, General and Comparative Endocrinology, vol. 187, pp. 39-47.

In order to monitor physiological stress, the authors of this study used enzyme-immunoassay (EIA) to detect faecal cortisol metabolite (FCM) concentrations in both captive and wild koalas. An adrenocorticotropic hormone (ACTH) challenge was used for biological validation of the FCM EIA. For captive koalas, sex, lactation status and handling status significantly affected FCM levels. Additionally, FCM levels did not differ significantly between wild and captive koalas.

  An ACTH challenge increased FCM concentrations 24 and 48 hours after injection for female and male koalas, respectively. This means that biologically relevant changes in koala FCM concentrations could be reliably measured by FCM EIA, with the prolonged excretory lag-time of FCM attributed to koala’s extensive gut system. While the FCM levels of non-lactating females were found not to be significantly affected by handling, in male koalas, FCM levels were 200% higher in individuals that were handled than in those that were not. Overall, the results indicate that handling has a significant effect on koala FCM levels.

  The sex-related differences in FCM levels observed in both captive and wild koalas may indicate intrinsic sexual differences in steroid metabolism, excretion routes and pituitary responsiveness. Additionally, the hyperreactivity of male koalas to handling might be related to their social behaviours, such as heightened aggression. Although short-term physiological stress is likely to have either no effect or even a positive effect on captive animals, chronic stress may have negative impacts on the animal’s physiology and welfare. FCM levels of animals in captivity are therefore important to monitor.

  The main implication of this study is that FCM EIA is a reliable and non-invasive tool for assessing physiological stress in koalas. The use of non-invasive stress endocrinology can not only help to assess the physiological effects of koala management strategies (e.g. translocation) but could also increase our understanding of the physiological stress responses of koalas to the captive environment. The authors also suggest that future studies could monitor seasonal changes in FCM in wild koalas using radio-tracking techniques to evaluate the effects of environmental variables on the physiological stress of the animal.

 

Summarised by Zilong Du

 

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