GOMES, F R; REZENDE, E L; BUNKERS, J L; GARLAND, T, Jr.; Univ. of California, Riverside: Organ Masses and Carbohydrate Metabolism of Mice Artificially Selected for High Voluntary Wheel Running

Selection experiments are a powerful tool for the study of microevolutionary processes, including the correlated evolution of behavior and morpho-physiological traits. To examine the microevolution of capacity for sustained exercise, we have selectively bred 4 replicate lines of house mice for high voluntary wheel running (S lines), while also randomly breeding 4 lines as controls (C lines). In the present study, we examined carbohydrate metabolism and organ masses of females (which always run more and faster than males in both S and C lines) from generation 35, sampled on the 6th day of exposure to running wheels, which mimics the way breeders are chosen. Analyses are in progress and so far indicate that S lines are smaller in total body mass (as reported previously) and have larger mass-corrected ventricles (a new result). Additionally, S-line individuals with the mini-muscle phenotype (homozygous for a Mendelian recessive allele that halves gastrocnemius muscle mass [Evolution, 2002, 56:1267-1275] while increasing per gram aerobic capacity [Am. J. Physiol. Regul. Integr. Comp. Physiol. 284:R433-R443]) tend to be smaller in total body mass but have significantly larger mass-corrected ventricles, livers, and soleus muscles. Because the importance of carbohydrates as metabolic fuel increases with the intensity of exercise in several mammalian species, we are also investigating the importance of glycogen depots from muscles and liver in sustaining voluntary wheel running. We aim to test the hypotheses that: (1) the rate and extent of glycogen depletion is higher in S lines; and (2) the extent of glycogen accumulation after exercise is higher in S lines. Supported by NSF IBN-0212567 to T.G.