METABOLISM, THERMOGENESIS AND DAILY RHYTHM OF BODY-TEMPERATURE IN THE WOOD LEMMING, MYOPUS SCHISTICOLOR

Wood lemmings (Myopus schisticolor) were captured during their autumnal migration in September and October. The animals were maintained at 12 degrees C and under 12L:12D photoperiod. Basal metabolic rate and thermogenic capacity of the wood lemming were studied. Basal metabolic rate was 3.54 ml O-2.g(-1).h(-1), which is 215-238% of the expected value. The high basal metabolic rate seems to be typical of rodents living in high latitudes. The body temperature of the wood lemming was high (38.0-38.8 degrees C), and did not fluctuate much during the 24-h recording. The high basal metabolic rate and the high body temperature are discussed with regard to behavioural adaptation to a low-quality winter diet. Thermogenic capacity, thermal insulation and non-shivering thermogenesis of the wood lemming displayed higher values than expected: 53.0 mW.g(-1), 0.53 mW. g(-1).degrees C-1 and 53.2 mW.g(-1), respectively. Brown adipose tissue showed typical thermogenic properties, although its respiratory property was fairly low, but mitochondrial protein content was high compared to other small mammals. The 24-h recording of body temperature and motor activity did not reveal whether the wood lemming is a nocturnal animal. Possibly, the expression of a circadian rhythm was masked by peculiar feeding behaviour. It is concluded that the wood lemming is well adapted to living in cold-temperature climates.