The thermal dependence of food assimilation and locomotor performance in southern grass lizards, Takydromus sexlineatus (Lacertidae)

Abstract

We collected southern grass lizards, Takydromus sexlineatus, from a population in Shaoguan (Guangdong, southern China), and used adult males and non-reproductive females to study the thermal dependence of food assimilation and locomotor performance. We did not find sex differences in selected body temperature (Tsel), critical thermal minimum (CTMin) and critical thermal maximum (CTMax). Tsel measured on a laboratory thermal gradient was 31.5°C; CTMin and CTMax averaged 6.4°C and 42.2°C, respectively. Within the range from 24°C to 36°C, food passage time, daily food intake, daily production of faeces, apparent digestive coefficient (ADC) and assimilation efficiency (AE) were affected by body temperature, and daily production of urates was not. Food passage time decreased with increase in body temperature within the range from 24°C to 34°C, and then increased at higher body temperatures. Lizards at 32°C and 34°C took more food than did those at higher or lower body temperatures. When influence of variation in the total food intake was removed by an ANCOVA, lizards at 36°C produced faeces containing significantly higher energy as compared with those at body temperatures lower than 32°C. Energy in urates did not differ among lizards at different body temperatures, when removing the influence of variation in total food intake by an ANCOVA. Lizards at 36°C had apparently lower ADC and AE than did those at body temperatures lower than 34°C, mainly because they produced faeces with higher energy contents. Sprint speed increased with increase in body temperature within the range from 20°C to around 32°C, and then decreased at higher body temperatures. Inter-specific comparison among three species of Takydromus lizards occupying different latitudinal (climatic) ranges reveal that (1) the maximal sprint speed is greater in T. wolteri and T. sexlineatus than in T. septentrionalis, (2) the optimal body temperature for sprint speed decreases with increase in latitude, and (3) the thermal sensitivity of sprint speed is more pronounced in species occupying lower and higher latitudinal ranges.