Interaction of Photoperiod, Temperature, Season, and Diel Cycles on the Thermoregulation of Water Snakes (Nerodia rhombifera)

Abstract

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