Thermal effects on embryogenesis and hatchlings of the grass lizard Takydromus stejnegeri (Squamata: Lacertidae) and implications of their potential for limiting its altitudinal distribution in Taiwan

Among the life stages of oviparous reptiles, embryo and hatchling are particularly susceptible to temperatures. Since temperature decreases with altitude, the upper altitudinal limit of some lowland species could be related to the temperature requirement for embryogenesis. The endemic grass lizard Takydromus stejnegeri is widely distributed at altitudes below 1000 m in Taiwan. In this study, we examined the thermal effects on embryogenesis of this species and evaluated its potential influence on current altitudinal distribution of T. stejnegeri. We measured some indices of embryogenesis and hatchling after incubation at 5 constant temperatures (15, 20, 25, 30, and 33°C). The results revealed that (1) hatching success increased with temperatures from 15°C to 20°C, reached 100% at 25°C and 30°C, and then declined at 33°C; and (2) the incubation duration increased with decreasing temperatures. Based on polynomial regression analysis, we predicted the development of embryos would cease at 16°C. Comparing the monthly average temperature at 3 different altitudes, we found that the T. stejnegeri would have an incubation success <100 % at areas higher than 1000 m (monthly average soil temperature < 25°C), and its eggs would not have enough time to hatch in the areas above 1600 m. We assumed that the temperature requirement for embryogenesis could be a limiting factor for the current altitudinal distribution of T. stejnegeri.