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We investigated the extent to which the changes in basal metabolic rate (BMR), gut morphology, andfood intake (FI) that typically occur during cold acclima tion in small mammals can be explained by the concept ofalimentary-mediated limits to sustainable metabolic energy expenditure. Adult short-tailedfield voles (Microtus agrestis) were cold stressed by continuous exposure to 5°C. Exposure for 10, 20, 50, and 100 d (n = 6 in all cases) produced significant changes in oxygen consumption ([102 ) , mass, FI, and the dry weight ofa variety ofmorpho logical parameters when compared with voles that were not cold exposed (n = 8). At 10°, 20°, and 25°C, V02 (mL· min-I) increased significantly with the duration ofcold exposure. After 100 d cold exposure, VOz had increased by more than 50% at each test temperature. Food intake (g. d- I) increased significantly by 106% after 10 d cold exposure but did not increase further with increased ex posure time. The ratio ofFI (j. h- I) to BMR (j. h- I) was 1.2 in controls and in creased to 2. 7 after 10 d cold exposure. Thereafter the ratio decreased, and after 100 d cold exposure FI:BMR was not significantly differentfrom control levels. The mass ofcold-exposed voles increased significantly with duration ojexposure. Masses ofthe following morphologicalparameters increased with increasing du ration ofcold exposure; whole body mass, carcass, skeleton, pelage, subcutaneous fat, liver, kidney, lung, and interscapular brown fat (BAT). There was no signifi cant relationship between duration ofcold exposure and the masses ofmuscle, large intestine, heart.and brain. Using stepwise multiple regression analysis we showed that variation in BMR was linked mostly to changes in skeletal mass. However, when skeletal mass was removed as an independent variable from the analysis, BAT, muscle, and gut mass entered as Significantpredictors, together explaining 55.5% ofthe uariatiori in BMR. Although FJ increased during cold ex posure, the increase (106%) was apparently insufficient to precipitate a hyper trophic response in the gut. Nevertheless BMR did increase as duration ofcold ex posure increased, probably linked to an increase in BAT mass and thus thermogenic capacity. We cannot support the hypothesis that the changes that typ |
