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 Yi-Huei Chen, Shu-Ping Huang, Mu-Hsuan Chang, and Ming-Chung Tu* Department of Life Science, National Taiwan Normal University, 88 Ting-Chow Rd., Sec. 4, Taipei 116, Taiwan (Accepted July 29, 2009) Yi-Huei Chen, Shu-Ping Huang, Mu-Hsuan Chang, and Ming-Chung Tu (2010) 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. Zoological Studies 49(3): 374-380. 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 inluence 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. http://zoolstud.sinica.edu.tw/Journals/49.3/374.pdf Key words: Thermal effect, Altitudinal distribution, Takydromus stejnegeri, Incubation temperature. *To whom correspondence and reprint requests should be addressed. Tel: 886-2-77346320. Fax: 886-2-29312904. E-mail:biofv026@ntnu.edu.tw T he distribution pattern of a species is normally related to environmental factors such as temperature, moisture, salinity, and oxygen partial pressure (Brown and Lomolino 1998). The environmental temperature is particularly important for the distribution patterns of ectothermic animals since it greatly influences body temperature and consequently physiological properties (Bennett 1980, Angilletta 2001) such as the metabolic rate, activity levels, and locomotor performance (Huey 1982, Lourdais et al. 2004). Because the thermal environment changes with altitude, it is reasonable to speculate that temperature plays an important role in the altitudinal distribution of reptiles. Temperature may limit the distribution by causing illness or death of animals. Thermal tolerance can be an important index for the altitudinal distribution of species, and this has mostly been tested in adult individuals (Huang et al. 2006 2007, Huang and Tu 2008a b). However, natural selection presumably acts on every stage of an animal’s life cycle (Packard et al. 1977). The thermal environment can influence stages in the life history other than the adult stage, such as the embryo and hatchling stages. Particularly in oviparous animals, the embryo stage is supposed to be a key stage because embryos are passively exposed to external environments for a long period Zoological Studies 49(3): 374-380 (2010) 374