Influence of pregnancy on the thermal biology of the lizard, <i>Sceloporus jarrovi</i>: why do pregnant females exhibit low body temperatures?

1. Selected body temperatures of female lizards, Sceloporus jarrovi , were measured on a photothermal gradient during late pregnancy and again when postpartum, and pregnant females were subjected to one of three fluctuating temperature regimes that simulated body temperatures of (1) pregnant females, (2) postpartum females or (3) allowed normal thermoregulation. 2. Overall, females selected lower body temperatures when pregnant (mean = 32·0°C) than when postpartum (mean = 33·5°C). 3. Females regulated body temperature more precisely when pregnant than when postpartum as judged by their smaller variances in body temperature throughout the day. 4. When pregnant, females selected a lower mean maximum body temperature (mean: pregnant = 32·8°C; postpartum = 34·5°C) than when postpartum, but selected mean minimum body temperatures did not differ. 5. None of the experimental temperature treatments was detrimental to pregnant females. Female body length increased during pregnancy but the rate of increase did not differ among treatments. Moreover, length‐adjusted body mass of postpartum females did not differ among treatments. 6. Pregnant females that experienced postpartum body temperatures produced neonates that were smaller in body mass and length than pregnant females that experienced pregnant body temperatures and females that were allowed to thermoregulate. 7. For neonates resulting from the postpartum body temperature treatment, the disparity in the body length, but not mass, was still observed at 9 days of age, although survival and growth of neonates was high and did not differ among treatments. 8. The results demonstrate that pregnant females could maintain higher postpartum body temperatures without compromising their physical condition, but select relatively low body temperatures, presumably to avoid decrements in offspring fitness.