ALBERT

Beschreibung: Body size is directly linked to key life history traits such as growth, fecundity, and survivorship. Identifying the causes of body size variation is a critical task in ecological and evolutionary research. Body size variation along altitudinal gradients has received considerable attention; however, the underlying mechanisms are poorly understood. Here, we compared the growth rate and age structure of toad-headed lizards ( Phrynocephalus vlangalii ) from two populations found at different elevations in the Qinghai-Tibetan Plateau. We used mark-recapture and skeletochronological analysis to identify the potential proximate causes of altitudinal variation in body size. Lizards from the high-elevation site had higher growth rates and attained slightly larger adult body sizes than lizards from the low-elevation site. However, newborns produced by high-elevation females were smaller than those by low-elevation females. Von Bertalanffy growth estimates predicted high-elevation individuals would reach sexual maturity at an earlier age and have a lower mean age than low-elevation individuals. Relatively lower mean age for the high-elevation population was confirmed using the skeletochronological analysis. These results support the prediction that a larger adult body size of high-elevation P. vlangalii results from higher growth rates, associated with higher resource availability. The proximate causes of altitudinal variation in body size in a Qinghai-Tibetan agamid lizard ( Phrynocephalus vlangalii ) were identified in this work. We found that slightly larger adult size of high-elevation lizards results from higher growth rates, associated with higher resource availability, rather than differences in newborn size, growth duration, and longevity.