Elevational variation in body size of Phrynocephalus vlangalii in the North Qinghai-Xizang (Tibetan) Plateau

We examined elevational and environmental aspects of body size variation in the Qinghai toad-headed lizard, Phrynocephalus vlangalii, using principal component analysis (PCA) of 9 morphological traits taken from 565 lizards from 17 populations. The first principal component (PCI) accounted for 67\% of the size variation in males and 62\% in females. For both males and females, PCI decreased with increasing elevation. When analyzed in relation with respect to environmental variables, body size showed positive relationship with temperature, air pressure, and activity season length, but showed weaker or inconsistent relationships with rainfall and humidity. The described pattern is the converse of Bergmann's rule for this lizard species and suggests that this body size pattern is driven by temperature, air pressure or length of the activity season.