BRZEK, P.*; BIELAWSKA, K.; KSIAZEK, A.; KONARZEWSKI, M.; Univ. of Bialystok, Poland; Univ. of Bialystok, Poland; Univ. of Bialystok, Poland; Univ. of Bialystok, Poland: Anatomic and molecular correlates of divergent selection for basal metabolic rate in laboratory mice

The question about the mechanisms of evolution of high level of basal metabolic rate (BMR) in endotherms is one of the most intriguing in evolutionary physiology. Since BMR mostly reflects metabolic activity of internal organs, evolutionary increase in BMR could have been realized by an increase in a relative organ size and/or in their mass-specific cellular metabolic rate. The latter may be mediated e.g. by an increase in the abundance of polyunsaturated fatty acids in cell membrane lipids, which determines the activity of many metabolically-important enzymes. We investigated the effect of divergent artificial selection for low (L-BMR) and high (H-BMR) BMR in laboratory mice (Mus musculus) on the size of internal organs and acyl composition of cell membranes. H-BMR mice had considerably higher body-mass specific mass of liver, kidney, heart and intestines. In contrast, both lines differed little in the acyl composition of total phospholipids from liver cell membranes. Contrary to the expectations, L-BMR mice showed significantly higher content of 20:3 and 22:6 polyunsaturated fatty acids. Residual variation in BMR, not explained by the liver mass, was negatively correlated with the abundance of 20:3 fatty acid. Thus, divergent selection for BMR did not affect the acyl composition of liver phospholipids in the direction, which may explain the observed variation in BMR. We conclude that a significant intra-specific variation in BMR may rapidly arise solely due to the changes in size of internal organs, without simultaneous modification of their mass-specific metabolic rate, related to the changes in cell membrane composition.