Effect of constant and fluctuating temperatures on resting and active oxygen consumption of toads, Bufo boreas

The relations of standard and active rates of oxygen consumption to body temperature (T_b) were tested in montane Bufo b. boreas and lowland Bufo boreas halophilus acclimated to constant T _b of 10, 20, or 30° C or to a fluctuating cycle of 5-30° C. Standard metabolic rates (SMR) of boreas acclimated to 30° C and halophilus acclimated to 10° C show pronounced regions of thermal independence but all other standard and active metabolic rates of groups acclimated to other thermal regimes are thermally sensitive. The SMR of both subspecies acclimated to the 5-30° C cycle are more thermally sensitive than those of similar individuals acclimated to constant T _b. In cases where the relation between SMR and T _b is linear for both halophilus and boreas at the same acclimation temperature, the slope and Q₁₀ of the relation for boreas are significantly higher than those of halophilus. Acclimation had little or no effect on the active metabolic rates of either subspecies. The relation between SMR and T _b of boreas maintained under field conditions (Carey, 1979) is matched only by those of individuals from the same population acclimated to 20° C.