DAILY AND SEASONAL RHYTHMS IN SELECTED BODY TEMPERATURES IN THE AUSTRALIAN LIZARD TILIQUA-RUGOSA (SCINCIDAE) - FIELD AND LABORATORY OBSERVATIONS

This study examined daily and seasonal activity and thermoregulatory b ehaviour of the sleepy lizard, Tiliqua rugosa, a large, diurnally acti ve temperate-dwelling Australian lizard, in the field and laboratory. Activity temperatures in the field were compared with those selected b y lizards in laboratory thermal gradients in order to assess the exten t to which endogenous versus exogenous factors contribute to seasonal variations in thermoregulatory behaviour. In the field, lizards are mo st active in late winter-spring (August-November), during which their activity varies from mostly unimodal on days of mild temperature to bi modal on hot days. In late spring-summer (November-January), activity is largely restricted to early morning, and at all other seasons sleep y lizards are rarely active. The winter-spring activity of sleepy liza rds is constrained by low environmental temperatures, as lizards at th ese seasons have low body temperatures in the field but higher tempera tures in laboratory thermal gradients. The lower temperatures selected in the laboratory in the summer-autumn months suggest the avoidance o f high ambient temperatures and general inactivity in the field at the se times. Thermal selection in the laboratory at the eight times of ye ar tested showed that the phase of the minimum and maximum temperature selected and the amplitude of the rhythm of temperature selected vari ed continuously with the time of year. These daily and seasonal shifts in thermoregulatory behaviour may be regulated by endogenous physiolo gical mechanisms coupled with seasonal ecological constraints such as food availability.