Parietalectomy and thermal selection in the lizard Sceloporus magister

Lizards were acclimatized to various regimes of temperature (15°, 35°C) and photoperiod (LD 08:16, 16:8). Parietalectomized, sham operated, and control animals were placed in thermal gradients and their body temperatures monitored for periods of up to 15 days. Daily rhythms of thermal selection were evident with higher temperatures selected in late photophase and lower temperatures selected in scotophase. Thermal selection was more variable in scotophase than in photophase. Parietalectomized lizards chose significantly higher body temperatures than did shams or controls. Acclimatization to temperature and photoperiod had little or no effect on the thermal preferendum. The preferred body temperature of controls was 33.2°C ± 3.59. Length of time in the gradient tended to change thermal preference, especially in lizards acclimated to 15°C. Through interactions with the pineal gland the parietal eye is probably important in synchronizing many bodily functions with photoperiod.