Chappell MA, Bachman GC (1994) Aerobic performance in Belding's ground squirrels (Spermophilus beldingi): variance, ontogeny, and the aerobic capacity model of endothermy. Physiological Zoology 68:421-442.
ABSTRACT -- We measured minimal resting oxygen consumption (VO2mr) and maximal oxygen consumption (VO2max) during exercise and thermogenesis in juvenile and adult Belding's ground squirrels (Spermophilus beldingi). VO2 and VO2max were highly correlated with body mass across a 5.2-fold mass range (80-419 g). However, an index of depot fat mass obtained from total body electrical conductivity measurements was not a significant predictor of VO2. The relationship between mass and VO2 was best described with two-phased regressions with inflections at 212-218 g (VO2mr and thermogenic VO2max) and 281 g (exercise VO2max). Variance was lowest for exercise VO2max and highest for VO2mr. The mass exponent for VO2mr in juveniles (0.911) was considerably higher than the allometric prediction of 0.67. Thermogenic VO2max averaged slightly higher than exercise VO2max. Mass exponents for both exercise and thermogenic VO2max were significantly higher than for VO2mr, and aerobic scope increased from about 5.4 in young animals (80-140 g) to about 7.5 in adults. Residual analysis revealed that VO2mr was significantly correlated to exercise VO2max, but not to thermogenic VO2max. These results provide limited support for the aerobic capacity model for the evolution of endothermy.