Diel variation in body temperature, thermal tolerance, and thermal dependence of locomotor performance in hatchling Chinese striped-necked turtles (Ocadia sinensis)
PAN Zhi-Chong ①② ZHANG Yong-Pu ①③ JI Xiang ①** (① School of Life Sciences, Hangzhou Normal College, Hangzhou 310036, China) (② School of Life Sciences, Ningbo University, Ningbo 315211, China) (③ Department of Biological and Environmental Sciences, Wenzhou Normal College, Wenzhou 325027, China)
We studied thermal tolerance and thermal dependence of locomotor performance of Chinese striped-necked turtle (Ocadia sinensis) hatchling, and designed two thermal environments, one with and one without thermal gradients, to study diel variation in body temperature (Tb). Body (cloacal temperature), water (Tw, where Tb was measured) and air (Ta, 1 cm above where Tb was measured) temperatures were taken with the same RC-95 electronic thermometer (Shanghai Jinghua Instruments, China). The upper (CTMax) and lower (CTMin) limits of thermal tolerance were 41.9 ℃ and 1.8 ℃, respectively. In the environment with thermal gradients, there was significant diel variation in body, water and air temperatures, and daily means of body and water temperatures were nearly the same, both exceeding the daily mean of air temperature. Significant variation in body, water and air temperatures were also found in the environment without thermal gradients, but there were no significant differences in daily means of body, water and air temperatures. The existence of thermal gradients was a necessary condition for turtles to behaviorally regulate body temperatures within their voluntary range. Selected body temperature (Tsel) varied from 25.4 ℃ to 29.2 ℃, with turtles exhibiting lower Tsel between 02:00 to 06:00 h than than at other times. Body temperatures were positively correlated with both water and air temperatures. ANCOVA showed that turtles in different thermal environments did not differ in Tw-specific body temperature, but Ta-specific body temperatures of turtles that were in the thermal gradients were on average 3.7 ℃ higher than those not in the thermal gradients. The locomotor performance of turtles was highly dependent on their body temperatures. Sprint speed increased with body temperature within the range of 18 to 39 ℃, decreasing at a body temperature of 41 ℃. Overall, turtles at relatively higher body temperatures had better locomotor performance than those at lower or extremely high body temperatures. A partial correlation analysis showed that sprint speed was positively correlated with both maximum length of continuous locomotion and the numbers of stops made by turtles on a racetrack. The maximum length of continuous locomotion was negatively correlated with the number of stops[Acta Zoologica Sinica 49(1):45-52,2003].