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. Ifthe physiology ofgeckos is evolutionarily adapted to these low and variable Tb 's, then thephysiology ofgeckos shouldfunction best at relatively low and variable temperatures. We tested a specific prediction of this hypothesis by comparing the thermal dependence ofsprint speed of nocturnal geckos versus diurnal lizards. In fact, optimal temperatures andperformance breadthsfor sprinting ofseveral geckos (Coleonyx brevis, C. variegatus, Hemidactylus frenatus, H. turcicus, Lepidodactylus lugubris) do not differ substantiallyfrom those of diurnal lizardsfrom otherfamilies. As a result geckos normally forage at night atTb 's that should be suboptimalfor sprinting. Potential evolutionary explanations (e.g., evolutionary inertia of thermalphysiology, possible selection pressures favoring high optimal temperatures)for the similarity of the thermal dependence of sprinting ofgeckos and diurnal lizards are evaluated.