Temperature and light effects on the circadian rhythm and locomotory activity of the plains garter snake(Thamnophis radix hayendi)

Abstract

The Locomotory activity of the Plains Garter snake was determined under L/D: 12/12 conditions at five constant temperatures and three light intensities during the light period. The snakes were diurnal at low temperatures with nocturnal activity increasing in various amounts at higher temperatures. The different light intensities had relatively small effects on the activity rhythm. Activity was recorded under four constant light conditions at five constant temperatures and the characteristics of the free‐running rhythm measured. A comparison of the characteristics of the free‐running rhythm to Aschoff's circadian rule indicates that this snake is an exception to this rule. Increase light intensity decreased total activity under all conditions. Under a L/D: 12/12 cycle the decrease in activity was more pronounced during the dark period than the light period. It is suggested that crepuscular or nocturnal activity shown by snakes at high temperatures may be an effect the temperature level has on the biological clock and activity controlling mechanisms rather than temperature selection by the snake.