Ecophysiology of Australian Arid-Zone Marsupials

Abstract

Studies of the ecophysiology of Australia's marsupials are still in their infancy but recent work has focused on the question of stress in species inhabiting arid and semi-arid environments. An operational definition of stress as ‘the physiological resultant of demands that exceed an animal’s homeostatic capacities’ has been used here to search for instances of stress in arid-zone marsupials due to high temperatures and lack of water. Significant perturbations of water and electrolyte balance in arid-zone marsupials were found to be rare, and, even in the driest year ever recorded on Barrow Island, only one species, the Barrow Island euro, showed signs of an increased allostatic load, but not ‘allostatic overload’, or stress. The Spectacled hare-wallaby, serves as an exemplar of the level of adaptation by some arid-zone marsupials, having the lowest rate of water loss yet recorded for any mammal worldwide. This contrasts with the Rothschild’s rock wallaby, which lacks hormonal control over water loss by the kidney but survives in a similar habitat to that of the hare wallaby by its reliance during daylight hours on cool and humid caves and rockpile shelters to conserve water. Arid-zone marsupials thus appear physiologically and behaviourally well buffered to withstand the rigours of their habitat, but the environmental changes wrought by European colonisation of the continent increasingly put these adaptations to the test.