Aspects of temperature regulation in mice selected for large and small size

We measured traits involved in physiological and behavioural thermoregulation in the 6 replicates of a selection experiment for large and small size (6-week weight) in mice, including control lines (18 lines in all). The observed genetic correlations between body size and thermoregulatory traits are consistent with a thermoregulatory advantage of large size, including decreased weight-specific food consumption and increased nest-building, with no change in body temperature. The differences in food consumption were closely paralleled by differences in amount of brown adipose tissue, strongly suggesting that much of the decreased efficiency of the small lines is due to heat production by brown fat. These results are consistent with available observations on natural populations, that selection for temperature adaptation probably has had some influence on body size in this species.