EXERCISE PHYSIOLOGY OF WILD AND RANDOM-BRED LABORATORY HOUSE MICE AND THEIR RECIPROCAL HYBRIDS

We conducted a ''common garden'' experiment to compare aspects of exercise physiology and voluntary wheel-running behavior in wild and random-bred (i.e., non-inbred) laboratory house mice and their reciprocal crosses. Analysis of covariance indicated that, after effects of body mass and other appropriate covariates (e.g., age at testing) were accounted for, wild (range 2.46-3.30 m/s, n = 12) and hybrid (range 1.69-3.30 m/s, n = 24) mice exhibited forced maximal sprint running speeds that averaged similar to 50% higher than those of random-bred laboratory mice (range 1.11-2.12 m/s, n = 19). Wild and hybrid mice also had significantly higher (+ 22%) mass-corrected maximal rates of oxygen consumption (VO2max) during forced exercise and greater (+ 12%) relative ventricle masses than lab mice. Wild and hybrid mice also showed statistically higher swimming endurance times relative to body mass than lab mice, although these differences were insignificant when body mass was not used as a covariate. No significant differences were found for relative gastrocnemius muscle mass, liver mass, hematocrit, or blood hemoglobin content. During a 7-day test on voluntary activity wheels, both wild and hybrid mice ran significantly more total revolutions (+ 101%), ran at higher average velocities when they were active (+ 69%), and exhibited higher maximum revolutions in any single 1-min period (+ 41% on the 7th day of testing), but the total number of active 1-min intervals did not differ significantly among groups. In general, the behavioral and/or whole organism performance traits showed greater differences than the lower-level traits; thus, during the domestication of house mice, behavior may have evolved more rapidly than physiology.