Influence of torpor on daily energy expenditure of the dasyurid marsupial Sminthopsis crassicaudata.

Daily torpor is an energy-conserving mechanism, used by many small marsupials to reduce energy expenditure during adverse environmental conditions. Since little is known about how much energy is actually saved by torpor in marsupials and how this is related to the duration of torpor bouts, we investigated the effect of ambient temperature (Ta) on different metabolic states and the effect of torpor bout duration in Sminthopsis crassicaudata (16 g) on average daily metabolic rate (ADMR). Ta had a significant effect on the active and resting metabolic rates (MR), both being higher at Ta 12 degrees C than Ta 18 degrees C (P < 0.001, t-test). In contrast, the ADMR at Ta 12 degrees C and Ta 18 degrees C did not differ significantly, and it appears that the increased cost for thermoregulation in normothermic active and resting animals at Ta 12 degrees C was compensated by a decrease in MR during torpor. Torpor bout duration was negatively correlated with ADMR. Torpor bouts of 5 hr reduced ADMR by 12-16%. Torpor bouts of more than 10 hr reduced ADMRs by 30-50%. Our study shows that torpor can significantly reduce daily energy expenditure in S. crassicaudata, and this may be important for the survival of this species in the wild.