Do Desert Geckos Conserve Energy and Water by Being Nocturnal?

Abstract

Body temperature has a very large effect on the rate of energy metabolism of ectothermic animals. Nocturnal lizards, which have low body temperatures when they are active at night, may have lower daily energy requirements than do diurnal lizards, which maintain high body temperatures while active during daylight hours. We tested the hypothesis that the nocturnal desert gecko Ptyodactylus hasselquistii has lower energy and water needs than do diurnal desert lizards by comparing doubly labeled water measurements of field metabolic rates (FMRs) and water fluxes for both groups. The FMRs and water influx rates of the geckos were statistically indistinguishable from those of diurnal iguanid lizards. We suggest that field observations of daily time and activity budgets, and thermal regimes, be made to permit evaluation of this surprising finding.