TEMPERATURE SELECTION AND USE OF TORPOR BY THE MARSUPIAL SMINTHOPSIS-MACROURA

Many small mammals display daily torpor to minimize energy expenditure during the rest phase when faced with unfavorable environmental condi tions. However, given a choice of thermal environments, it is not clea r whether these daily heterotherms select ambient temperatures that mi nimize metabolic rates during torpor or ambient temperatures that mini mize metabolic rates during normothermia. It is also not clear whether they prefer being normothermic or torpid. In this study, we investiga ted temperature selection, activity patterns, body temperature pattern s, and the use of torpor in Sminthopsis macroura in a thermal gradient when food was freely available or restricted. Animals employed torpor regularly immediately after cessation of activity even when excess fo od was provided. Nevertheless, they selected high ambient temperature near the zone of thermoneutrality during both normothermia and torpor. Reduced food supply did not affect either temperature preference or t otal activity, but it did result in significantly prolonged torpor bou ts. In addition, it lowered the daily minimum body temperature during torpor by about 2 degrees C. Our study shows that S. macroura selected a high ambient temperature to reduce energy costs during normothermia . Nevertheless, daily torpor was frequently employed at the high tempe rature, especially when food was restricted. (C) 1998 Elsevier Science Inc.