Chappell MA, Dawson TJ (1994) Ventilatory accommodation of changing oxygen consumption in dasyurid marsupials. Physiological Zoology 67:418-437.
ABSTRACT -- Little is known about how the mammalian ventilatory system accommodates the large change in rates of oxygen consumption (VO2 ) between minimal and maximal aerobic metabolism. These changes are expected to be particularly large in marsupials, which have a substantially greater aerobic scope than similar-sized placental mammals. We measured ventilation and VO2 at metabolic rates between basal metabolism (BMR) and maximal oxygen consumption during thermogenesis (VO2max) in three dasyurid marsupials: Planigale tenuirostrus (5.7 g), Sminthopsis crassicaudata (14.2 g), and Antechinus swainsoni (66.9 g). Comparative data on a fourth dasyurid species, Dasyuroides byrnei (144 g) were obtained from the literature. Thermogenic aerobic scopes (VO2max/BMR) were 9.2, 9.0, 8.7, and 10.4, respectively. Ventilatory accommodation of changing VO2 was qualitatively similar in the four species, with most accommodation resulting from changes in minute volume (Vi). However, there were differences in the relative importance of frequency (f), tidal volume (Vt), and oxygen extraction (EO2 ) in accommodation. In all species, f and Vt were strongly correlated to VO2 . Tidal volume was significantly correlated to VO2 in S. crassicaudata, A. swainsoni, and D. byrnei, while EO2 was significantly correlated to VO2 only in A. swainsoni. Analysis of factorial ventilation changes across a standardized 8-fold change in VO2 revealed overall similarity between the four species in Vt and Vi, with significant differences in f and EO2. For the latter two parameters, there was no difference between P. tenuirostrus and S. crassicaudata, while A. swainsoni and D. byrnei differed significantly from other species. As size increases in dasyurids, EO2 increases, mass-specific Vt decreases, and the importance of Vt changes in accommodation increases. When compared to a generalized allometry for ventilation in resting placental mammals, dasyurids had much lower f and greater Vt than predicted; in the two smaller species resting EO2 was lower than predicted. However, when the dasyurids were compared to data obtained from 10 placental mammals measured without the use of restraints or invasive procedures, there were no differences between the two taxa. We found no indication that ventilation constrained thermogenic VO2max.