Behavioral Thermoregulation Increases Growth Rate in a Nocturnal Lizard

We tested the hypothesis that thermoregulation increases growth rate in nocturnal lizards. Leopard geckos (Eublepharis macularius) maintained from hatching at 25 C grew at a rate of 0.11 g/day, while geckos allowed to thermoregulate at preferred body temperatures (30 C for 13.5 h per day) grew 1.5 times as fast (0.16 g/day). Long-term thermal treatment had a significant reverse acclimation effect on preferred body temperature (Tp): Tp was 1.2 C lower in thermoregulatory individuals than in those kept at 25 C. Feeding and time of day also had significant but minor effects on Tp. Despite their nocturnal ecology, leopard geckos seem to be typical among lizards in requiring a diurnal heat source for maximal growth. This result provides a physiological explanation for the observation that some nocturnal lizards thermoregulate in burrows during the day, and may have implications for the biogeography of nocturnal ectotherms.