Resting metabolic rate and morphology in mice (Mus musculus) selected for high and low food intake

We investigated the relationship between resting metabolic rate (RMR) and v arious morphological parameters in non-breeding mice, selected for high and low food intake corrected for body mass. RMR was measured at 30 degreesC, and mice were subsequently killed and dissected into 19 body components. Hi gh-food-intake mice had significantly greater body masses and a significant ly elevated RMR compared with the low-intake mice. Data pooled across strai ns indicated that body mass, sex and strain together explained over 56% of the observed variation in RMR. The effects of strain and sex on RMR and tis sue morphology were removed, and three separate statistical analyses to inv estigate the relationship between RMR and organ morphology were performed: (i) employing individual regression analysis with each tissue component as a separate predictor against RMR; (ii) individual regression analysis with residual organ mass against residual RMR (i.e. with strain, sex and body ma ss effects removed); and (iii) pooling of some organ masses into functional groupings to reduce the number of predictors. Liver mass was the most sign ificant morphological trait linked to differences in RMR. Small intestine l ength was significantly greater in the high-intake line; however, no differ ence was observed between strains in the dry mass of this organ, and there was no evidence to associate variability in the mass of the alimentary trac t with variability in RMR. The effects of strain on RMR independent of the effect on body mass were consistent with the anticipated effect from the st rain differences in the size of the liver.