INTERACTION OF PHOTOPERIOD, TEMPERATURE, SEASON, AND DIEL CYCLES ON THE THERMOREGULATION OF WATER SNAKES (NERODIA-RHOMBIFERA)

Diamondback water snakes (Nerodia rhombifera) were acclimatized with d ifferent photoperiods and temperatures during different seasons. Body temperatures (T-b) were measured at 10-min intervals for two days. In summer, shortened photoperiod alone did not influence the grand mean T -b but reduced the amplitude of the diel cycle. When we decreased accl imation temperature only, a lower mean T-b was selected but the amplit ude of daily rhythm remained unchanged. Paradoxical combinations of ph otoperiod and temperature (e.g., short day length and low temperature in summer season) did not alter overall T-b but did influence the ampl itude of the daily cycle. Snakes selected significant higher T-b in su mmer than in winter. More precise thermoregulation was observed during scotophase than during photophase in summer with normal acclimatizati on (longer day length, higher temperature). Photoperiod had no effect on thermoregulatory precision, but lower temperature reduced precision .