Effects of incubation temperature on embryonic development rate, sex ratio and post-hatching growth in the Chinese three-keeled pond turtle, Chinemys reevesii

Understanding the effects of incubation temperature on embryos and hatchlings may have important implications for husbandry and conservation in turtles. Unfortunately, such knowledge is deficient for most Asian turtles. We incubated eggs of the Chinese three-keeled pond turtle (Chinemys reevesii) at 6 constant temperatures (24, 26, 28, 30, 32 and 34 °C) to test for the effects of embryonic thermal environment on incubation duration, hatching success, hatchling size and mass, sex ratio and post-hatching growth. Incubation duration (ID) decreased nonlinearly as the temperature (T) increased, and could be estimated by the equation: ID = 42.74 exp (4.30 / (T - 17.28). Eggs incubated at 32 °C and 34 °C had lower hatching success than those at 24 °C, 26 °C and 28 °C. The turtle showed a Male-Female pattern of temperature-dependent sex determination (MF or TSDIa), with male bias at low temperatures (24 °C and 26 °C), and female bias at high temperatures (30 °C, 32 °C, and 34 °C). The relationship between sex ratio (SR) and temperature (T) could be estimated by a nonlinear equation, SR = 0.025 + 0.923 / (1 + exp (- (T - 30.03) / 0.009))^ 0.006. Hatchlings from eggs incubated at 24, 26 and 28 °C were larger and heavier than their counterparts at 30 °C, 32 °C and 34 °C. However, the temperature influence on hatchling size disappeared when the turtles were 3 months old, while most hatchlings from eggs incubated at 34 °C did not survive. After 3 months, female turtles from 30 °C and 32 °C grew faster than did male turtles from 24 °C and 26 °C; females from 28 °C grew significantly faster than males from the same temperature. In contrast, there was no difference in growth rate either within females or within males from different temperatures. The dichotomy of growth rate between turtles from high vs low temperatures are thus largely attributed to between-sex difference rather than temperature effects. Taken together, our results indicate that the temperatures ranging from 28 to 30 °C are most suitable for egg incubation in C. reevesii, because of the high hatchability and post-hatching survival, and the fastest growth of hatchlings in these thermal regimes. Small hatchling turtles may catch up in the subsequent post-hatching growth if provided with a suitable husbandry environment, given that turtle size at hatching is not a determinant of growth in this species.