Effect of ambient temperature on the body temperature rhythm of male gray mouse lemurs (Microcebus murinus)

In order to cope with the seasonal variations in ambient temperature and food availability in the natural habitat gray mouse lemurs (Microcebus murinus) exhibit adaptive energy-saving mechanisms similar to those in hibernating species with seasonal and daily heterothermia. To determine thermoregulatory responses, via telemetry we recorded body temperature and locomotor activity variations during the breeding season in three captive male mouse lemurs kept at ambient temperatures (T-a ranging from 18 degrees to 34 degreesC. Rhythms in body temperature and locomotor activity were clearly exhibited regardless of ambient temperature. As T-a increased, mean body temperature increased from 36.5 +/- 0.1 degreesC to 37.6 +/- 0.3 degreesC, with significant change in the amplitude of the body temperature rhythm when T-a rose above 28 degreesC. Effects of T-a were mostly due to changes in the fall in body temperature occurring daily at the beginning of the light phase when the subjects entered diurnal sleep. The daily decrease in body temperature was not modified by exposure to ambient temperatures from 18 degreesC to 28 degreesC whereas it disappeared tinder warmer condition. Changes in locomotor activity levels only delayed the occurrence of thermoregulatory modulation. These results strongly suggest that, during the breeding season, the thermoneutral zone of mouse lemurs is close to 28 degreesC and that the diurnal fall in body termperature could be considered as an important adaptive energy-saving mechanism adjusted to ecological constraints.