Sexual dimorphism and female reproduction in two sympatric toad-headed lizards, Phrynocephalus frontalis and P. versicolor (Agamidae).

We studied sexual dimorphism and female reproduction in two sympatric species of toad-headed lizards, Phrynocephalus frontalis and P. versicolor, from Inner Mongolia, North China. The smallest reproductive females of P. frontalis and P. versicolor we recorded were 43.5 mm and 44.2 mm SVL, respectively. Females were the larger sex in P. versicolor, whereas female and male adults of P. frontalis did not differ in mean SVL. Females of P. frontalis were on average smaller than females of P. versicolor, so were males of P. frontalis. In both species females were larger in abdomen length (AL) but smaller in head length (HL), head width (HW) and tail length (TL); adults of P. frontalis were larger in HL and TL but smaller in AL and HW than adults of P. versicolor of the same size. Females of both species laid a single clutch of 2-6 eggs per breeding season. The trade-off between size and number of eggs was evident in both species. Of the examined female reproductive traits, only clutch size and egg size differed between the two species, with females of P. frontalis laying fewer but larger eggs than did females of P. versicolor of the same SVL. However, as the observed between-species difference in egg size (and thus, offspring size) was small, any niche divergence resulting from this difference could be less important in reducing competitions between these two sympatric species of lizards. [ABSTRACT FROM AUTHOR]