Exercise physiology of wild and random-bred laboratory house mice and their reciprocal hybrids

Abstract

m/s, n = 24) mice exhibited forced maximal sprint running speeds that averaged ~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 (VOzmax > 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 'I-day test on voluntary activity wheels, both wild and hybrid mice ran significantly more total revolutions (+ lOl%), 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. behavior; directional dominance; domestication; endurance; evolution; locomotion; maximal oxygen consumption; sprint speed; wheel running LABORATORY HOUSE MICE have served as model organisms in numerous physiological, behavioral, and quantitative genetic studies (12, 25, 35, and references therein). In exercise physiology, laboratory rats have been used more commonly than mice (4). For logistical reasons, however, mice are better candidates for study of the quantitative genetic basis of variation in physiological and associated behavioral traits. As a prelude to quantitative genetic analyses and artificial selection experiments with random-bred, genetically variable laboratory house mice, we conducted a series of studies to establish baseline information and to consider how appropriate a random-bred strain of mice may be for drawing evolutionary conclusions about metabolism and exercise physiology in small mammals (16, 22, 31, cf. 35). In this study we present information on the exercise capacities and associated behavioral traits of a strain of random-bred laboratory mice compared with a Wisconsin population of wild (commensal) house mice and with hybrids between the lab and wild mice.

Maximal sprint speeds and muscle fiber composition of wild and laboratory house mice

“…As part of a larger research program using house mice as a model system for quantitative genetic analyses (10) of questions derived from evolutionary physiology (13,15,21) have compared a randombred strain of laboratory house mice (Hsd:ICR) with wild mice captured from a commensal Wisconsin population. In this comparison, we also found many differences, such as the lab mice being larger at all ages postweaning and displaying less voluntary activity on running wheels (11,35). Of the traits studied in these previous comparisons, forced maximal sprint running speed (measured on a photocell-lined racetrack) showed the largest difference, with wild mice averaging over twice as fast as the lab mice and the distributions of speeds showing no overlap (11).…”

“…In this comparison, we also found many differences, such as the lab mice being larger at all ages postweaning and displaying less voluntary activity on running wheels (11,35). Of the traits studied in these previous comparisons, forced maximal sprint running speed (measured on a photocell-lined racetrack) showed the largest difference, with wild mice averaging over twice as fast as the lab mice and the distributions of speeds showing no overlap (11). The purpose of the present study was to determine whether this difference was reflected at the level of muscle fiber composition.…”

“…We studied house mice (Mus domesticus) of four types, as described in detail in the companion papers (11,35). Laboratory mice were of the randombred, genetically variable Hsd:ICR strain, purchased from Harlan Sprague-Dawley, Indianapolis, IN (Bldg.…”

“…Analysis of variance (ANOVA) and analysis of covariance (ANCOVA) were used to compare mean values of the four groups; these analyses were implemented both in the ONEWAY and ANOVA (which allows covariates) procedures of SPSS, and with dummy variables in a multiple regression using the REGRESSION procedure. The two hybrid groups were compared to check for possible maternal effects (see 11,35).…”

“…This lack of correlation is consistent both with theoretical expectations [Ch. 9 of (2), references in (16)] and with most empirical comparisons within and across species of mammals (16 and references therein), including our previous studies of Hsd:ICR house mice (10,11,13). For example, in a quantitative genetic study of 347 Hsd:ICR mice (10), log maximal sprint speed was not significantly correlated with log body mass (r = 0.050; 2-tailed p = 0.357).…”