Thermoregulation by kangaroos from mesic and arid habitats: Influence of temperature on routes of heat loss in eastern grey kangaroos (Macropus giganteus) and red kangaroos (Macropus rufus)
Tj. Dawson et al., Thermoregulation by kangaroos from mesic and arid habitats: Influence of temperature on routes of heat loss in eastern grey kangaroos (Macropus giganteus) and red kangaroos (Macropus rufus), PHYSIOL B Z, 73(3), 2000, pp. 374-381
We examined thermoregulation in red kangaroos (Macropus rufus) from deserts
and in eastern grey kangaroos (Macropus giganteus) from mesic forests/wood
lands. Desert kangaroos have complex evaporative heat loss mechanisms, but
the relative importance of these mechanisms is unclear. Little is known of
the abilities of grey kangaroos. Our detailed study of these kangaroos' the
rmoregulatory responses at air temperatures (T-a) From -5 degrees to 45 deg
rees C showed that, while some differences occur, their abilities are funda
mentally similar. Both species show the basic marsupial characteristics of
relatively low basal metabolism and body temperature (T-b). Within the ther
moneutral zone, T-b was 36.3 degrees +/- 0.1 degrees C ((X) over bar +/- SE
) in both species, and except for a small rise at T-a 45 degrees C, T-b was
stable over a wide range of T-a. Metabolic hear production was 25% higher
in red kangaroos at T-a -5 degrees C. At the highest T-a (45 degrees C), bo
th species relied on evaporative heat loss (EHL) to maintain T-b; both pant
ing and licking were used. The eastern grey kangaroo utilised panting (76%
of EHL) as the principal mode of EHL, and while this was so for red kangaro
os, cutaneous evaporative heat loss (CEHL) was significant (40% of EHL). CE
HL appeared to be mainly licking, as evidenced from surface temperatures. B
oth species utilised peripheral vascular adjustments to control heat flow,
as indicated by changes in dry conductance (C-dry). At lower temperatures,
C-dry was minimal, but it increased significantly at T-a just below T-b (33
degrees C); in these conditions, the C-dry of red kangaroos was significan
tly higher than that of eastern grey kangaroos, indicating a greater relian
ce on dry heat loss. Under conditions where heat flows into the body from t
he environment (T-a 45 degrees C), there was peripheral vasoconstriction to
reduce this inflow; C-dry decreased significantly from the values seen at
33 degrees C in both kangaroos. The results indicated that, while both spec
ies have excellent thermoregulatory abilities, the desert red kangaroos may
cope better with more extreme temperatures, given that they respond to T-a
45 degrees C with lower respiratory evaporation than do the eastern grey k
angaroos.