Effects of temperature acclimation on maximum heat production, thermal tolerance, and torpor in a marsupial

Marsupials, unlike placental mammals, are believed to be unable to increase heat production and thermal performance after cold-acclimation. It has been suggested that this may be because marsupials lack functional brown fat, a thermogenic tissue, which proliferates during cold-acclimation in many placentals. However, arid zone marsupials have to cope with unpredictable, short-term and occasionally extreme changes in environmental conditions, and thus they benefit from an appropriate physiological response. We therefore investigated whether a sequential two to four week acclimation in 'Sminthopsis macroura' (body mass approx. 25 g) to both cold (16°C) and warm (26°C) ambient temperatures affects the thermal physiology of the species. Cold-acclimated 'S. macroura' were able to significantly increase maximum heat production (by 27%) and could maintain a constant body temperature at significantly lower effective ambient temperatures (about 9°C lower) than when warm-acclimated. Moreover, metabolic rates during torpor were increased following cold-acclimation in comparison to warm-acclimation. Our study shows that, despite the lack of functional brown fat, short-term acclimation can have significant effects on thermoenergetics of marsupials. It is likely that the rapid response in 'S. macroura' reflects an adaptation to the unpredictability of the climate in their habitat.