Ventilatory accommodation of oxygen demand and respiratory water loss in kangaroos from mesic and arid environments, the eastern grey kangaroo (Macropus giganteus) and the red kangaroo (Macropus rufus)
Tj. Dawson et al., Ventilatory accommodation of oxygen demand and respiratory water loss in kangaroos from mesic and arid environments, the eastern grey kangaroo (Macropus giganteus) and the red kangaroo (Macropus rufus), PHYSIOL B Z, 73(3), 2000, pp. 382-388
We studied ventilation in kangaroos from mesic and arid environments, the e
astern grey kangaroo (Macropus giganteus) and the red kangaroo (Macropus ru
fus), respectively, within the range of ambient temperatures (T-a) from -5
degrees to 45 degrees C. At thermoneutral temperatures (T-a = 25 degrees C)
, there were no differences between the species in respiratory frequency, t
idal volume, total ventilation, or oxygen extraction. The ventilatory patte
rns of the kangaroos were markedly different from those predicted from the
allometric equation derived for placentals. The kangaroos had low respirato
ry frequencies and higher tidal volumes, even when adjustment was made for
their lower basal metabolism. At T-a > 25 degrees C, ventilation was increa
sed in the kangaroos to facilitate respiratory water loss, with percent oxy
gen extraction being markedly lowered. Ventilation was via the nares; the m
outh was closed. Differences in ventilation between the two species occurre
d at higher temperatures, and at 45 degrees C were associated with differen
ces in respiratory evaporative heat loss, with that of M. giganteus being h
igher. Panting in kangaroos occurred as a graded increase in respiratory fr
equency during which tidal volume was lowered. When panting, the desert red
kangaroo had larger tidal volumes and lower respiratory frequencies at equ
ivalent T-a than the eastern grey kangaroo, which generally inhabits mesic
forests. The inference made from this pattern is that the red kangaroo has
the potential to increase respiratory evaporative heat loss to a greater le
vel.