The Influence of Light and Temperature on Diel Activity Rhythms in the Sand Boa, Eryx conicus

Abstract

ABSTRAcr.-In the nocturnal snake Eryx conicus the light-dark cycle was a more effective synchronizer of activity than were fluctuations in temperature. Under a light-dark cycle and constant temperature, the temperature level influenced the amplitude of the rhythm but did not affect the phasing of activity. Consequently under low constant temperature the rhythm became damped but a mainly nocturnal pattern was retained. There was little evidence that the activity rhythms synchronized by light-dark or temperature cycles persisted under constant conditions. Circadian rhythms in behavioral and physiological functions are generally considered to be a ubiquitous feature of living organisms. Such rhythms are synchronized by environmental time cues, but are endogenous and display their own freerunning periodicity under constant conditions. The term diel refers to those rhythms in which an endogenous component has yet to be demonstrated. In reptiles both temperature fluctuations and the light-dark cycle (LD) may act as time cues, and the influence of these parameters on rhythmic patterns of locomotor activity has been documented for many lizards and some chelonians (Rusak, 1981). However, little attention has been paid to the regulation of activity in snakes. This may be partly due to the fact that these reptiles may display considerable intraspecific variation and imprecision in rhythmic behavior, making them difficult subjects for such studies (Heckrotte, 1975). Daily activity patterns in the vipers Vipera latastei and Apis cerastes have been documented by Saint Girons (1954, 1959). He emphasizes the role of thermoregulation in the activity patterns of