Seasonal changes in thermoregulation and maximum metabolism in the yellow-necked field mouse

Abstract

Seasonal changes in thermoregulation efficiency and basal meta-bolism rate (BMR) were studied in Apodemus flavicollis (Melchior, 1834). The animals had significantly greater body weight in winter than in summer and the body weight of females differed significantly from that of males. The average rectal temperature in winter was 37.0Ż1.6 °C. There were two cases of spontaneous decrease in rectal temperature to 31.5 and 34.2 °C. During the experiments carried out in helium-oxygen mixture, a decrease in body temperature to as much as 15 and 12 °C was noted, without lethal effect. The maximum thermogenesis values extrapolated to —20 °C in summer reached 11.6±0.8 ccm CteXg-iXhr-1 and extrapolated to—30 °C in winter reached 13.4+1.6 ccm OzXg-iXhr-i. BMR in summer (2.9±0.3 ccm OaXg-iXhr" 1) did not differ significantly from that determined in winter (3.0±0.4 ccm ChXg-iXhr -1). In summer, themaximum metabolism was four times higher, and in winter four and half times higher t'hat the BMR.