Oxygen consumption and thermoregulatory responses in three species of South American marsupials

Oxygen consumption (VO2), body temperature (Tb) and wet thermal conductance (Cwet), under resting conditions, exposure to low ambient temperature (Ta) and during sustained exercise (treadmill running) were measured in three phylogenetic related (same family; Didelphidae) South American marsupials possessing similar body masses: Caluromys philander (arboreal/fruit and insect eating), Philander opossum (terrestrial and arboreal/omnivore), and Metachirus nudicaudatus (terrestrial/omnivore). Our measurements of VO2 and Cwet under resting conditions agree with those previously reported for other marsupials. We expected that C. philander would show a lower maximal sustained VO2, compared to the other two species, based on its more reduced skeletal muscle mass. However, the values obtained for C. philander were not statistically different (ANOVA) from those obtained for the other two species. When exposed to low ambient temperature (12 °C), differences among the three species were detected, i.e., M. nudicaudatus did not survive, while the other two species were able to reduce their Tb under such conditions. C. philander gradually decreases its Tb when cold exposed, and P. opossum shows a more pronounced Tb drop only when exposure to low ambient temperatures occurs for a more prolonged period of time.