Dehydration,with and without heat,in kangaroos from mesic and arid habitats: different thermal responses including varying patterns in heterothermy in the field and laboratory |
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Authors: | Terence J Dawson Cyntina E Blaney Hugh C K McCarron Shane K Maloney |
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Institution: | (1) School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney, 2052, NSW, Australia;(2) Physiology M311, School of Biomedical and Chemical Science, University of Western Australia, Crawley, 6009, WA, Australia |
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Abstract: | Field data showing the daily patterns in body temperature (T
b) of kangaroos in hot, arid conditions, with and without water, indicate the use of adaptive heterothermy, i.e. large variation
in T
b. However, daily T
b variation was greater in the Eastern Grey Kangaroo (Macropus giganteus), a species of mesic origin, than in the desert-adapted Red Kangaroo (Macropus rufus). The nature of such responses was studied by an examination of their thermal adjustments to dehydration in thermoneutral
temperatures (25°C) and at high temperature (45°C) via the use of tame, habituated animals in a climate chamber. At the same
level of dehydration M. rufus was less impacted, in that its T
b changed less than that for M. giganteus while it evaporated significantly less water. At a T
a of 45°C with water restriction T
b reached 38.9 ± 0.3°C in M. rufus compared with 40.2 ± 0.4°C for M. giganteus. The ability of M. rufus to reduce dry conductance in the heat while dehydrated was central to its superior thermal control. While M. giganteus showed more heterothermy, i.e. its T
b varied more, this seemed due to a lower tolerance of dehydration in concert with a strong thermal challenge. The benefits
of heterothermy to M. giganteus were also limited because of thermal (Q10) effects on metabolic heat production and evaporative heat loss. The impacts of T
b on heat production were such that low morning T
b’s seen in the field may be associated with energy saving, as well as water saving. Kangaroos respond to dehydration and heat
similarly to many ungulates, and it is apparent that the accepted notions about adaptive heterothermy in large desert mammals
may need revisiting. |
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Keywords: | Kangaroos Marsupials Thermoregulation Dehydration Respiration Heterothermy |
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