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 (T-p): T-p was 1.2 C lower in thermoregulatory individuals than in Chose kept at 25 C. Feeding and time of day also had significant but minor effects on T-p. 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.