Circadian rhythms of locomotor activity and temperature selection in sleepy lizards, Tiliqua rugosa

Apr 26, 2007Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology

Daily patterns of movement and temperature choice in sleepy lizards

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Abstract

Lizards displayed robust daily rhythms of locomotor activity and thermoregulation under constant darkness.

Lizards maintained their activity and thermoregulation rhythms when transferred from a light:dark cycle to constant darkness.
Most lizards exhibited free-running circadian rhythms during a 13-day period of constant darkness.
The activity pattern observed in light conditions was unimodal and persisted in darkness.
Mean skin temperature and locomotor activity levels decreased from light:dark to constant darkness, but activity duration remained the same.
A close correlation was found between circadian activity and thermoregulatory rhythms, suggesting they may be regulated by the same internal mechanisms.

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This study examined whether the daily rhythms of locomotor activity and behavioural thermoregulation that have previously been observed in Australian sleepy lizards (Tiliqua rugosa) under field conditions are true circadian rhythms that persist in constant darkness (DD) and whether these rhythms show similar characteristics. Lizards held on laboratory thermal gradients in the Australian spring under the prevailing 12-hour light : dark (LD) cycle for 14 days displayed robust daily rhythms of behavioural thermoregulation and locomotor activity. In the 13-day period of DD that followed LD, most lizards exhibited free-running circadian rhythms of locomotor activity and behavioural thermoregulation. The predominant activity pattern displayed in LD was unimodal and this was retained in DD. While mean levels of skin temperature and locomotor activity were found to decrease from LD to DD, activity duration remained unchanged. The present results demonstrate for the first time that this species' daily rhythm of locomotor activity is an endogenous circadian rhythm. Our results also demonstrate a close correlation between the circadian activity and thermoregulatory rhythms in this species indicating that the two rhythms are controlled by the same master oscillator(s). Future examination of seasonal aspects of these rhythms, may, however, cause this hypothesis to be modified.

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Circadian rhythms of locomotor activity and temperature selection in sleepy lizards, Tiliqua rugosa

Abstract

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