Temperature Regulation and Torpidity in the Pygmy Mouse, Baiomys taylori

Abstract

The average weight of 13 pygmy mice, Baiomys taylori, was 6.4 [plus or minus] 1.31 g. Length of daily torpor was proportional to the quantity of food and moisture presented. Animals resisted a drop in body temperature below 22[degree] C, a level above which spontaneous arousal could be readily elicited. The Q10 for metabolism of torpid animals was 2.1 at a body temperature 3.2 [plus or minus] 1.0[degree] C above ambient temperature. Spontaneous arousals required 45 to 60 minutes and the maximum rate of increase in body temperature was 0.34[degree] C/minute. The thermal neutral zone of the pygmy mouse extends from 29 to 36[degree] C and the average metabolic rate for 10 animals weighing 7.3 [plus or minus] 1.59 g is 1.95 [plus or minus] 0.38 cc 02/g hour. The thermal conductance ranged from 0.40 cc 02/g hour degree to 0.48 cc 02/g hour degree. Body temperatures for non-torpid animals were between 32 and 36[degree] C. The lowest heart rate, 300 beats per minute, occurred at the upper end of the thermal neutral zone. The maximum heart rate of a resting animal, 756 beats per minute, was recorded at an ambient temperature of 13[degree] C. The heart rates of torpid animals were between 75 and 100 beats/minute at ambient temperatures of 15 to 20[degree] C. The respiratory rate was lowest at a TA of 33[degree] C, 100 breaths/ minute. The maximum recorded rate was 360 breaths/minute at a TA of 13[degree] C. A stroke volume of 11.3 ul and a cardiac output of 3.4 cc/ minute was calculated from measurements of metabolic rate, heart rate, heart weight, and estimates of utilization and stroke fraction (cc blood/g of heart/beat).