METABOLISM AND THERMOREGULATION IN CROSSES BETWEEN WILD AND RANDOM-BRED LABORATORY HOUSE MICE (MUS-DOMESTICUS)

We conducted a ''common garden'' experiment to compare aspects of ther moregulation and metabolism in wild and random-bred laboratory, house mice (Mus domesticus) and their reciprocal crosses. Analysis of covari ance (ANCOVA) indicated that, after accounting for effects of body mas s and other appropriate covariates (e.g., age), wild (N = 12) and hybr id (N = 25) mice together tended to have higher (+9.7%; P = .0904) max imal nonshivering thermogenesis (max-NST) in response to norepinephrin e injection than did lab mice (N = 18). Wild (-17.2%; P = .0941) and h ybrid (wild dam: -23.1%; P = .0001; lab dam: -11.2%; P = .0749) mice a lso tended to have lower basal metabolic rates (BMRs) than did lab mic e. As a consequence of these trends, wild and hybrid mice, analyzed to gether, had significantly higher (+18.2%; P = .0263) regulatory NST (m ax-NST minus BMR) than did lab mice. Paralleling the differences in re gulatory NST, wild and hybrid mice together had significantly more (+2 1.2% P = .0129) interscapular brown adipose tissue than did lab mice. However, plasma thyroid hormone levels (triiodothyronine [T-3] and thy roxine [T-4]) showed no significant differences among groups, and even for the traits that exhibited significant differences, the overlap of values for individual mice was substantial. Moreover, mean values for max-NST and BMR for all four groups fell well within the range of val ues reported in the literature for small mammals We therefore conclude d that random-bred laboratory mice are not necessarily ''degenerate'' with respect to their metabolic and thermoregulatory capacities. Final ly, the two reciprocal cross groups differed in BMR (P = .0314), which thus indicated a maternal influence: wild-dam X lab-sire mice had sig nificantly lower BMRs than did lab-dam X wild-sire mice.