Daily rhythms of metabolic rate and body temperature of two murids from extremely different habitats.

Daily circadian rhythms of body temperature (Tb) and oxygen consumption (VO2) were measured in two murid species, which occupy extremely different habitats in Israel. The golden spiny mouse (Acomys russatus) is a diurnal murid distributed in arid and hot parts of the great Syrio-African Rift Valley, while the broad-toothed field mouse (Apodemus mystacinus) is a nocturnal species that inhabits the Mediterranean woodlands. In both species, the daily rhythms of Tb and VO2 are entrained by the photoperiod. Under laboratory experimental conditions (ambient temperature Ta = 33 degrees C and photoperiod regime of 12L:12D), Acomys russatus exhibits a tendency towards a nocturnal activity pattern, compared to the diurnal activity displayed by this species under natural conditions. Under the same photoperiod regime and at Ta = 28 degrees C, Apodemus mystacinus displays nocturnal activity, as observed under natural conditions. The maximal values of Tb were recorded in Acomys russatus at midnight (23:50 h), while the maximal values of VO2 were recorded at the beginning of the dark period (18:20 h). In Apodemus mystacinus, the maximal values of Tb and VO2 were recorded at 23:40 and 20:00 h, respectively. The ecophysiological significance of these results is discussed further.