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)

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.