Thermal Biology of Nocturnal Ectotherms: Is Sprint Performance of Geckos Maximal at Low Body Temperatures?

Nocturnal geckos are active with body temperatures Tb that are low and variable relative to those of diurnal lizards. If the physiology of geckos is evolutionarily adapted to these low and variable Tb's, then the physiology of geckos should function best at relatively low and variable temperatures. We tested a specific prediction of this hypothesis by comparing the thermal dependence of sprint speed of nocturnal geckos versus diurnal lizards. In fact, optimal temperatures and performance breadths for sprinting of several geckos (Coleonyx brevis, C. variegatus, Hemidactylus frenatus, H. turcicus, Lepidodactylus lugubris) do not differ substantially from those of diurnal lizards from other families. As a result geckos normally forage at night at Tb that should be suboptimal for sprinting. Potential evolutionary explanations (e.g., evolutionary inertia of thermal physiology, possible selection pressures favoring high optimal temperatures) for the similarity of the thermal dependence of sprinting of geckos and diurnal lizards are evaluated.