The effect of body temperature on the locomotory energetics of lizards

Summary

• 1. Oxygen consumption ($\dot V_{O_2 }$), carbon dioxide production ($\dot V_{CO_2 }$), and stamina were measured in the lizardTupinambis nigropunctatus running at sustainable and non-sustainable velocities (v) on a motor-driven treadmill. Three experimental groups were measured: field-fresh animals at body temperature (T _b)=35°C and laboratorymaintained animals atT _b=35 and 25 °C.

• 2. Mean preferredT _b was determined to be 35.2 °C.

• 3. At 35 °C, field-fresh animals had a greater maximal oxygen consumption ($\dot V_{O_{2 } max corr}$) (4.22 vs 3.60 ml O₂ g^−0.76 h⁻¹) and a greater endurance. The net cost of transport (slope of$\dot V_{O_2 } v^{ - 1}$ onv) did not differ between the groups (=2.60 ml O₂ g^−0.76 km⁻¹). Velocity at which$\dot V_{O_{2\max } }$ is attained (MAS) is 0.84 km h⁻¹. The respiratory exchange ratio (R) exceeded 1.0 atv above MAS, indicating supplementary anaerobic metabolism.

• 4. At 25 °C,$\dot V_{O_{2 } max corr}$ was lower (2.34 ml O₂ g^−0.76 h⁻¹) as was endurance, MAS occurring at 0.5 km h⁻¹. Net cost of transport was not significantly different than at 35 °C.

• 5. The effect ofT _b on locomotory costs was analyzed for this lizard and other species. It was concluded that the net cost of transport is temperature independent in all species examined and the total cost of locomotion$\dot V_{O_2 } v^{ - 1}$ is temperature dependent inTupinambis (Q₁₀=1.4–2.0) and all other species examined except one. The energetic cost of locomotion [($\dot V_{O_2 active} - \dot V_{O_2 rest}$)v ⁻¹], previously reported to be temperature independent in lizards, is temperature dependent inTupinambis (Q₁₀=1.3–1.6) and in two other species.

• 6. Previous work has interpreted the energetic cost of locomotion as reflecting thermally independent costs of muscle force generation in vivo. These conclusions are questioned on both their generality and their practical and theoretical bases.