Embryonic thermosensitivity and hatchling morphology differ between two coexisting lizards

We incubated eggs of two coexisting lizards, Phrynocephalus frontalis and Phrynocephalus versicolor, at three constant temperatures (24, 28 and 32 °C) to examine whether they differ in embryonic thermosensitivity and hatchling morphology. Eggs incubated at the three temperatures produced morphologically different hatchlings in P. versicolor but not in P. frontalis. Snout-vent length (SVL), body mass and head width were greater in P. versicolor hatchlings from the 24 °C treatment than those from the 32 °C treatment when accounting for differences in initial egg mass, and tail length was smaller in P. versicolor hatchlings from the 24 °C treatment than those from the 32 °C treatment when accounting for differences in final egg mass. Body mass, head length, head width, tail length, fore-limb length and hind-limb length were greater in P. frontalis hatchlings than in P. versicolor hatchling when accounting for differences in initial or final egg mass. Moreover, P. frontalis females produce larger hatchlings than do P. versicolor females of the same SVL not only by laying larger eggs, but also by investing more dry materials (and thus, more energy) into the egg. Given a link between interspecific competition (and niche restriction) and morphology, it seems likely that morphological differences at hatching may facilitate the coexistence of the two lizards. The two lizards differed in embryonic thermosensitivity and water uptake by eggs during incubation, suggesting that they use different microhabitats in the area of sympatry.