2.1 Study system, sites and collection of lizards
The Mongolian racerunner (E. argus ), a relatively small (up to 70mm snout-vent length [SVL]) oviparous lacertid lizard, is widely distributed across China and its environs (Zhao, 1999). the Mongolian racerunner has been reported across the north‐northeast to the south (Jiangsu) and the west (Qinghai) of China (Zhao, 1999). Across the Chinese borders, the Mongolian racerunner has also been reported around the region of Lake Baikal in Russia, Mongolia, and Korea (Zhao et al., 2011) within grassland and farmland habitats and arid and semiarid regions (Zhao, 1999). Mongolian racerunners are widely distributed across altitude in China (Fig. 1), ranging from sea level to ca. 3000 m asl (Zhao et al., 1999). The Mongolian racerunner lizard populations across China are relatively homogeneous in their genetic structure (Zhao et al., 2011) but show significant variation in morphology, physiology, life histories, and feeding habits across geographic gradients (Wang et al., 2020).
We collected 432 female E. argus lizards between 2011 through 2021 from nine field locations across China, varying in altitude and environmental conditions (Fig. 1). During our field studies from May to July each year, we collected only non-gravid female E. arguslizards and transported them to field stations in the study areas. We measured the snout-vent length (SVL; ±0.01 mm) of collected female lizards in the field station laboratory, after which we released them at the site from where they were captured. We collected and measured the body sizes of E. argus female lizards across populations with altitudinal gradients ranging from 30 – 2979m above sea level (asl), with 60 records from Shidu, 26 from Xingtai, 14 from Jingtai, 36 from Harbin, 31 from Hebei, 25 from Liaoyang, 44 from Chuzhou, 106 from Erdos, and 90 from Gonghe (Table S1).