Shifts of thermogenesis in the prairie vole (Microtus ochrogaster)

The weight-specific oxygen consumption ( \(\mathop V\limits^ \bullet _{{\rm O}_2 } \) ) of prairie voles caught in winter is 24% higher at 27.5° C and 29% higher at 7.5° C than that of summer animals, thus affording a higher weight-specific thermogenesis in winter than in summer which may allow tolerance to lower thermal exposures. Coincident with the increase in weight-specific rates of oxygen consumption is a decrease in body weight. When total energetic cost to maintain an animal per unit time is calculated, the cost at 27.5° C is the same for both summer and winter animals. Further, the cost to maintain an animal at 7.5° C is less in winter than in summer. Arguments are presented suggesting that prairie voles compensate for increased weight-specific thermogenesis in winter by lowering body weight. The responses to thermal acclimation are quite different in summer and winter animals, thus implying different sorts of metabolic organization. Acclimation to 5° C effects a 26% increase in \(\mathop V\limits^ \bullet _{{\rm O}_2 } \) at 27.5° C of winter voles, and acclimation to 30° C does not change \(\mathop V\limits^ \bullet _{{\rm O}_2 } \) . In contrast, \(\mathop V\limits^ \bullet _{{\rm O}_2 } \) at 27.5° C of summer animals is unaffected by 5° C acclimation, and depressed 20% by 30° C acclimation. Thus, the animals are capable of considerable physiological adjustment to varying thermal conditions in different seasons.