Meeting Abstract
54.1 Saturday, Jan. 5 Locomotor Constraints in Mice Selected for High Voluntary Wheel Running DLUGOSZ, E.M.*; CHAPPELL, M.A.; GARLAND, T, Jr.; University of California, Riverside; University of California, Riverside; University of California, Riverside edlug001@ucr.edu
An expectation from studies of locomotor physiology is that highly mobile animals should evolve adaptations to facilitate running, such as changes in limb structure and muscle function. We investigated whether a unique muscle phenotype (“mini-muscles”) that evolved under selective breeding for high voluntary wheel running has improved running efficiency in laboratory mice, Mus domesticus. More than 45 generations of selection has produced 4 replicate selected (S) lines that run more than twice as far per day as 4 non-selected control lines. The mini-muscle phenotype, which results from an autosomal recessive Mendelian allele, occurs in 2 of the S lines and has become fixed in one of these. In homozygotes, hindlimb muscle mass is halved but mass-specific oxidative capacity of mixed hindlimb muscle is doubled. We hypothesized that reduced hindlimb mass in mini-muscle mice would lessen the energy costs of limb cycling during running and hence reduce costs of transport (COT). We measured slopes (incremental COT, or iCOT) and intercepts of the metabolic rate vs. speed relationship during voluntary wheel running, as well as sprint speed on a photocell-timed racetrack, in 30 S-line females, ten of which showed the mini-muscle phenotype. As expected from reduced hindlimb muscle mass, mini-muscle mice tended to have slower sprint speeds. However, contrary to predictions, mini-muscle mice had higher COT than mice with normal-muscle phenotypes, mainly due to higher zero-speed intercepts and postural costs (intercept � resting metabolic rate). Both phenotypes had similar iCOT. These results show that mice with altered limb morphology after intense selection for running long distances do not necessarily run more efficiently. Supported by NSF grant IOB-0543429.
