Water and electrolyte homeostasis and kidney function of desert-dwelling marsupial wallabies in Western Australia

Prolonged drought, necessitating conservation of water, is one of the major environmental challenges faced by many Australian marsupials. Radioactive isotopes of water and sodium were used to assess the ability of two species of marsupial wallabies to maintain water and electrolyte balance during pe riods of extreme water deprivation in the arid Pilbara region of Western Au stralia. The spectacled hare-wallaby, Lagorchestes conspicillatus, has the lowest mass-specific rate of water turnover at 27.5 ml.kg(-0.82).day(-1) ye t reported for any mammal and was two to three orders of magnitude lower th an that of the Rothschild's rock-wallaby, Petrogale rothschildi. Studies of renal function show that the hare-wallaby conserves water by producing a h ighly concentrated urine under the influence of lysine vasopressin (LVP), t he anti-diuretic hormone (ADH) in macropodid marsupials. In contrast, rock- wallabies show unusual renal responses to water deprivation, with no change in LVP levels and a limited response to water deprivation involving a redu ction in renal plasma flow and glomerular filtration rate, with no signific ant change in tubular function. Both species are able to maintain water and electrolyte homeostasis during periods of drought, highlighting the effica cy of their differing adaptive solutions to the problem of water scarcity, although the hare-wallaby is superior to the rock-wallaby in this respect. Rock-wallabies appear to rely primarily on behavioural rather than physiolo gical responses for their survival in the Pilbara and appear to be more vul nerable to extinction in the event of significant habitat modification. The secure nature of their rock habitat, however, means that they have suffere d less than hare-wallabies in the recent past.