Elaphe bimaculata (Colubridae) is a small rat snake (60-80 cm) found in China. We collected adult E. bimaculata from a population in Jiangsu, Eastern China, to study the effect of incubation temperature on hatchlings' metabolism and behavior. We incubated the eggs at their constant temperatures (24, 27 and 30 ℃). All hatchlings were used to evaluate the response to chemical cues, respiration metabolism and sex determination. Because physiological and behavioral performances are highly sensitive to variation in body temperature in reptiles, we conducted all trials at the body temperature of 28 ℃. This was achieved by placing hatchlings in an incubator at the test temperature for approximately 1h prior to the test. We presented a cotton-tipped applicator soaked with cologne water to the lip of hatchlings and recorded tongue flicks for 1 min. Tongue flicking was measured because many reptiles flick their tongues frequently to detect both predators and prey and to gather information about other members of their own species. This behavioral character is therefore a potentially important indicator of fitness.
Selected body temperature was examined in a 100 cm × 60 cm × 60 cm terrarium covered with sand, sward and pieces of clay tiles. The terrarium was placed in constant temperature rooms where the temperature was set at 24 ℃. One light bulb (200 W) suspended above one end created a thermal gradient ranging from room temperature to 50 ℃ for 12h daily, and lights were switched on at 07:00 h. Snakes were moved from the cool side into the terrarium at 10:00 h and, 24 h later, they were measured for body temperature (cloacal temperature, Tb) at 13:00 h using a UT-325 electronic thermometer (made in Taiwan) individually, which had an external thermal probe and was previously calibrated with a standard thermometer. Great care was taken to avoid heat transfer occurring between hands and the measuring snake. Hereafter, we continuously measured the temperature of hatchling snakes for three days.
Our results reveal that there were no significant differences in the effects of incubation temperature (24-30 ℃) on hatchlings' tongue flicks, selected body temperature, respiration metabolism and the initial feeding in E. bimaculata. The amount of carbon dioxide was decreased with the increase of age from nativity to residual yolk, and the amount of carbon dioxide decreased to minimum value when the hatchlings' residual yolk was absolutely exhausted. The amount of carbon dioxide breathed out by hatchlings incubated at 24, 27 and 30 ℃ was 10.58、12.06 and 10.88 μL/min respectively. Influences of incubation temperatures on hatchling initial feeding was negligible; the weight of preys were 4.92, 4.34 and 3.60 g and the proportion of predation was 46.2%, 56.3% and 40% by hatchlings incubated at 24, 27 and 30 ℃ respectively. Our results reveal that the effects of incubation temperature (24-30 ℃) on hatchlings behavior and feeding are not significant in E. bimaculata. E. bimaculata fit to live in this temperature range.