KONARZEWSKI, M.; KSIAZEK, A.; LAPO, I.B.; University of Bialystok; University of Bialystok; Institute of Genetics and Animal Breeding PAS: Artificial selection for basal metabolic rate in laboratory mice
To study the consequences of genetic manipulation of basal metabolic rate (BMR) we subjected laboratory mice to un-replicated, divergent selection for body mass-corrected BMR. In generation F0 narrow sense heritability of BMR, estimated by parent-offspring regression was 0.12 and statistically significant. In F19 the selection resulted in between-line difference in BMR equivalent to 2.5 phenotypic SD units. BMR was negatively correlated with the peak metabolic rate and positively correlated with food consumption and masses of metabolically active viscera: kidneys, liver, small intestine and heart. Repeatability of BMR measurements increased in the course of selection, which suggests that it was itself an unintentionally selected trait. We argue that despite the lack of replication, our findings demonstrate that BMR is a measure of energetic costs of maintenance of metabolic machinery necessary to sustain high levels of energy expenditure, and that correlated responses were strong enough to claim the existence of genetic correlations. We illustrate the usefulness of our selection with the results of experiment, in which mice of both lines were suddenly exposed (without prior acclimation) to ambient cold. Mice responded to cold-exposure by a considerable increase in food consumption and a hypertrophy of internal organs. However, metabolic loads imposed on these organs (indexed as the ratio of energy consumption to the mass of the organ) were much greater in low-BMR than high-BMR line. Thus, under the same metabolic demand low-BMR mice were much closer to exhaustion of their metabolic capacities than high-BMR mice. The use of selected mouse lines provided us with a unique opportunity to analyze the consequences of genetically determined differences in BMR and the sizes of viscera for the utilization and function of physiological safety margins.
