The influence of ambient temperature and humidity on the body temperature and water loss from two Australian lizards, Tiliqua rugosa (Gray) (Scincidae) and Amphibolurus barbatus cuvier (Agamidae)

Abstract

Tiliqua rugosa and Amphibolurus barbatus are capable of living in arid habitats; they display modified behaviour and corresponding physiological adaptations. The activity pattern of T. rugosa changes during the year with activity restricted during midsummer to short periods in the early morning and late afternoon. The body temperature of T. rugosa under natural conditions indicates that 41°C is the highest temperature tolerated naturally. In the controlled temperature cabinet a lizard of this species survived for 2 hr at a body temperature of 41.7°C, whilst the lethal temperature was 45.5°C. For A. barbatus the lethal temperature was 46.0°C, and one specimen survived for 2 hr at 43.5°C. The thermoregulation temperature (T.T.) of T. rugosa as calculated from field data was 37.5°C; above this temperature the body temperature of this lizard was below that of the air. Temperature regulation in this species was also studied in the laboratory under controlled conditions. Water loss by evaporation was remarkably low in both lizards even when compared with better adapted, desert lizards. The rate of water loss is directly related to temperature and inversely related to humidity. T. rugosa loses most water during the first period of exposure (about 2 hr) to temperatures between 30-37.5°C, whilst A. barbatus loses water more slowly. At high temperatures (i.e. over 40°C) the rate of water loss decreases. Even in areas where no surface water is available T. rugosa appears to survive because its varied diet supplies adequate water. It is unlikely that food is a limiting factor in its distribution.