The effect of body temperature on the locomotory energetics of lizards

1. Oxygen consumption ( {Mathematical expression}), carbon dioxide production ( {Mathematical expression}), and stamina were measured in the lizard Tupinambis 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 at T_b=35 and 25 °C. 2. Mean preferred T_b was determined to be 35.2 °C. 3. At 35 °C, field-fresh animals had a greater maximal oxygen consumption ( {Mathematical expression}) (4.22 vs 3.60 ml O₂ g^-0.76 h^-1) and a greater endurance. The net cost of transport (slope of {Mathematical expression} on v) did not differ between the groups (=2.60 ml O₂ g^-0.76 km^-1). Velocity at which {Mathematical expression} is attained (MAS) is 0.84 km h^-1. The respiratory exchange ratio (R) exceeded 1.0 at v above MAS, indicating supplementary anaerobic metabolism. 4. At 25 °C, {Mathematical expression} 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 of T_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 {Mathematical expression} is temperature dependent in Tupinambis (Q₁₀=1.4-2.0) and all other species examined except one. The energetic cost of locomotion [( {Mathematical expression})v^-1], previously reported to be temperature independent in lizards, is temperature dependent in Tupinambis (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.