Seasonal changes in the thermoenergetics of the marsupial sugar glider, Petaurus breviceps

Little information is available on seasonal changes in thermal physiology a nd energy expenditure in marsupials. To provide new information on the subj ect, we quantified how body mass, body composition, metabolic rate, maximum heat production, body temperature and thermal conductance change with seas on in sugar gliders (Petaurus breviceps) held in outdoor aviaries. Sugar gl iders increased body mass in autumn to a peak in May/June, which was caused to a large extent by an increase in body fat content. Body mass then decli ned to minimum values in August/September. Resting metabolic rate both belo w and above the thermoneutral zone (TNZ) was higher in summer than in winte r and the lower critical temperature of the TNZ occurred at a higher ambien t temperature (T-a) in summer. The basal metabolic rate was as much as 45% below that predicted from allometric equations for placental mammals and wa s about 15% lower in winter than in summer. In contrast, maximum heat produ ction was raised significantly by about 20% in winter. This, together with an approximately 20% decrease in thermal conductance, resulted in a 13 degr eesC reduction of the minimum effective T-a gliders were able to withstand. Our study provides the first evidence that, despite the apparent lack of f unctional brown adipose tissue, sugar gliders are able to significantly inc rease heat production in winter. Moreover, the lower thermoregulatory heat production at most Ts in winter, when food in the wild is scarce, should al low them to reduce energy expenditure.