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Locomotor Performance and Activity Energetics of Helodermatid Lizards

Daniel D. Beck, Michael R. Dohm, Theodore Garland, Jr., Aurelio Ramírez-Bautista and Charles H. Lowe
Copeia
Vol. 1995, No. 3 (Aug. 18, 1995), pp. 577-585
DOI: 10.2307/1446755
Stable URL: http://www.jstor.org/stable/1446755
Page Count: 9
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Locomotor Performance and Activity Energetics of Helodermatid Lizards
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Abstract

Locomotor performance and activity energetics were analyzed in 19 individual helodermatid lizards ranging in mass from 24.5-1220 g. We measured maximum sprint speeds, endurance on a treadmill, cost of transport, and aerobic capacity ($\dot{{\rm V}}{\rm O}_{2}{\rm max}$) at a mean body temperature of 30.8 C. The maximum sprint speed for both Heloderma species averaged 1.7 km/h, which is among the lowest recorded for lizards. A typical Heloderma had an endurance time of 16.0 min at 1.0 km/h, which is higher than expected for a lizard of this size at 31 C. At lower speeds, adult Heloderma could run for prolonged periods. The cost of transport for a 500 g Heloderma at 0.4 km/h was 0.46 ml O2 g -1 km-1, which is comparable to the cost of transport in other lizards. The two Heloderma species showed no significant differences in $\dot{{\rm V}}{\rm O}_{2}{\rm max}$, cost of locomotion, endurance, or sprint speeds. Neither cost of locomotion nor aerobic capacity differed between captive and wild Heloderma. At 31 C, helodermatids had a high $\dot{{\rm V}}{\rm O}_{2}{\rm max}$, resulting in the highest factorial aerobic scope (30.4) of any lizard measured to date. The high aerobic capacity of Heloderma seems surprising for a sedentary lizard but may be advantageous during intensive male-male agonistic behaviors. Males had significantly higher $\dot{{\rm V}}{\rm O}_{2}{\rm max}$ than did females, suggesting that sexual selection may favor males with high aerobic capacities.

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