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 fo od availability in the natural habitat gray mouse lemurs (Microcebus murinu s) exhibit adaptive energy-saving mechanisms similar to those in hibernatin g species with seasonal and daily heterothermia. To determine thermoregulat ory responses, via telemetry we recorded body temperature and locomotor act ivity variations during the breeding season in three captive male mouse lem urs kept at ambient temperatures (T-a ranging from 18 degrees to 34 degrees C. Rhythms in body temperature and locomotor activity were clearly exhibite d regardless of ambient temperature. As T-a increased, mean body temperatur e increased from 36.5 +/- 0.1 degreesC to 37.6 +/- 0.3 degreesC, with signi ficant 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 i n 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 2 8 degreesC whereas it disappeared tinder warmer condition. Changes in locom otor activity levels only delayed the occurrence of thermoregulatory modula tion. These results strongly suggest that, during the breeding season, the thermoneutral zone of mouse lemurs is close to 28 degreesC and that the diu rnal fall in body termperature could be considered as an important adaptive energy-saving mechanism adjusted to ecological constraints.