Use of Anaerobic Metabolism by Free-Ranging Lizards

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Abstract
We measured whole-body lactic acid concentrations of two species of iguanid lizards and two species of teiids in the field during routine and experimentally manipulated activities. Lactate concentrations were lowest when lizards first emerged in the morning. Routine foraging behavior produced small increases in lactate concentrations for all species. The teiids (Cnemidophorus exsanguis and C. sonorae) had significantly higher lactate concentrations at emergence and during routine activity than did the iguanids (Sceloporus virgatus and S. jarrovi). For S. virgatus lactate concentration during routine activity was positively correlated with the distance a lizard moved (0-16 m) during the half-hour period of observation before capture. Subduing and swallowing grasshoppers increased lactate concentrations of S. virgatus by an average of .121 mg/g, which was an increase of 40% over the average for routine activity. The magnitude of the increase was positively correlated with the size of the prey (.09-.48 g) but not with the time required (<1-35 min). Territorial defense by S. jarrovi doubled the average lactate concentration from .309 mg/g during routine activity to .653 mg/g after combat. Intensity of combat (measured as bites per minute by the resident lizard) was positively correlated with lactate concentration, but the duration of an agonistic encounter (1-15 min) was not. These data suggest that anaerobic metabolism can be an important pathway of energy input for lizards under natural conditions and support the hypothesis that physiological constraints can limit the behaviors available to a species of lizard.