摘要：

We studied thermal tolerance, body temperature, and thermal dependence of locomotor performance of hatchling red eared slider turtles ( Trachemys scripta elegans ). Two thermal environments, one with and the other without thermal gradients, were designed to study diel variation in body temperature (Tb) . Turtles were obtained from a pet shop in Hangzhou, with body mass, carapace length and carapace width being 9 5 ± 0 2 (7 7~11 1) g, 35 6 ± 0 2 (32 7~37 4) mm and 35 3 ± 0 2 (33 6~36 9) mm, respectively. Turtles were marked individually by toe clipping for future identification, and then were housed, 7~8 of them, in individual 50×30×30 cm 3 (length × width × height) glass cages, of which the bottom was filled with an oblique layer of sand (the maximum depth = 5 cm), water (the average depth = 2 5 cm) and debris to mimic natural conditions to some extent. The thermal gradients ranging from 18 °C to 60 °C were established by suspending two 250 W light bulbs at one end and approximately 20 cm above the bottom of the cage. Turtles in the environments either with or without thermal gradients were exposed to a natural light cycle, but those in the thermal gradients could regulate body temperatures within their voluntary range when the light bulbs were turned on. Body (cloacal temperature), water ( Tw, where turtles were measured for Tb ) and air ( Ta , 1 cm above the turtle measured for Tb ) temperatures were taken to nearest 0 1 °C, using a RC(95 electronic thermometer (Shanghai Jinghua Instruments, China), at intervals of 4 h in two consecutive days. The mean body temperature of active turtles in the thermal gradients was considered as the selected (or preferred) body temperature ( T sel) at the time. The upper ( CT Max, critical thermal maximum) and lower ( CT Min, critical thermal minimum) limits of thermal tolerance were determined in a LRH 250G incubator (Guangdong Medical Instruments, China), where turtles were cooled or heated from 28 °C at the rate 0 1 °C per min. During the experiments, we observed the behavior of the experimental turtles through a window on the door of the incubator. Body temperatures associated with a transient loss of righting response (the animals did not respond to intense mechanical stimulation and could not turn back when being turned over) at lower and upper thermal limits were used as endpoints for CT Min and CT Max. Locomotor performance was tested at 8 constant body temperatures (18, 22, 25, 30, 33, 36, 39 and 41 ℃), the sequence being randomized. Prior to each trial, turtles were placed in an incubator for a minimum of 4 h, thereby controlling their body temperatures at the expected level. Locomotor performance was assessed by chasing the turtles down a 200×10×15 cm 3 racetrack with one side transparent, which allow lateral filmation with a digital video camera (Panasonic NV DS77). It was always the same person (the second author) who chased the turtles, thereby standardizing the stimulus. The video tapes were later examined using the MGI VideoWave III software for sprint speed in the fastest 25 cm interval, number of stops in the racetrack and the maximum length of continuous locomotion. CT Max and CT Min were 41 9℃ and 1 8℃, respectively. Diel variation in body, water and air temperatures were found in the environments both with and without thermal gradients. In the environment with thermal gradients, the daily means of body and water temperatures were nearly the same, both being greater than the daily mean air temperature. In the environment without thermal gradients, body, water and air temperatures did not differ from each other in the daily mean value. The existence of thermal gradients is a necessary for turtles to regulate body temperatures within their voluntary range. T sel varied from 26 6 ℃ to 30 4 ℃, and it was lower during the period of 00:00 ～ 10:00 and higher at the other time phase in a 24 h cycle. Body temperatures were positively correlated with both water and air temperatures. An ANCO

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