Ontogenetic Shifts of Sexual Dimorphism in Phrynocephalus grumgrzimailoi(Agamidae)

Males and females of Phrynocephalus grumgrzimailoi from a population in Urumchi,Xinjiang,western China,differ in head size at the juvenile stage,with males having larger heads than females but females having larger venters. This sexual dimorphism is more pronounced in adults than in juveniles. Adults do not show a sexual dimorphism in snout-vent length(SVL) ,but males attain longer tails and shorter venters than females with the same SVL. An allometric growth pattern with SVL's increase is shown in the head size,tail length and venter size of both sexes. The growth rate of the head size becomes increasingly fast and the growth rate of tail length slower and slower with ontogeny. However,the venter grows increasingly faster in females but slower in males.