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Physiological Consequences of Thermoregulation in a Tropical Lizard (Ameiva festiva)

Ameiva festiva, a teiid lizard from Costa Rica, alternately basks in the sun at the edge of forests and then forages in the shade of the forest. We used this natural analog of behavior in a laboratory shuttle-box to examine the effect of thermoregulatory behavior on physiological and ecological performances of lizards in nature. We observed body temperatures (by radiotelemetry) and locomotor behavior in the field and measured the thermal dependence of sprint speed, stamina, and aerobic scope in the laboratory. The mean upper and lower threshold temperatures for shuttling in the field were 39.4 ± 0.97 C (95% confidence interval) and 34.5 ± 1.11 C (95% confidence interval), respectively, and corresponded to very high levels of sprint speed (90% of maximum speed), stamina, and aerobic scope. Nevertheless, the lizards apparently rarely use these high levels of locomotor capacity. Although these lizards are active foragers, their speed and duration of movement in the field fall far below the levels of speed and stamina that they achieved in the lab when measured at temperatures that they regularly experienced in the field. The only time that we observed an individual use its (apparently) full locomotor capacities was in a single high-speed, long-distance attempt at escape from a predator. Thus the locomotor capacities of Ameiva festiva may be analogous to the principle of excessive construction (sensu Gans), whereby the phenotypic capacities of animals are not shaped by routine activities but instead by rare events that may be critical to an animal's survival.