Life-history variation among three populations of the toad-headed lizard Phrynocephalus vlangalii along an elevation gradient on the northeastern Tibetan Plateau

Elevation and related environmental factors is a main factor for life-history variation in ectothermic species. To test if altitude can explain variation in life-history traits in the toad-headed lizard Phrynocephalus vlangalii, we sampled gravid females from three localities (Delingha: elevation 2910m, Daotanghe: 3367m; Maduo: 4257m) and measured parturition time, snout-vent length (SVL) at sexual maturity, female body size and postpartum body condition, litter size, litter mass, relative litter mass (RLM), size and mass of newborn offspring. Females gave birth between 25 July and 28 August, and females from lower elevations were earlier than those from higher elevations. Female SVL at sexual maturity and mean SVL, litter size, litter mass, relative litter mass and offspring size varied among populations, whereas female post-parturition body mass and offspring mass remained invariant. Females from the highest elevation had a greater SVL at sexual maturity, mean SVL and abdominal length. Both litter size and litter mass were positively correlated with female SVL. Females from the higher elevation localities (Maduo and Daotanghe) had a lower RLM than those from the lowest elevation (Delingha). Furthermore, females from the highest elevation produced fewer and larger (SVL but not mass) offspring than those from the other localities. Trade-offs between offspring size and number were detected in Delingha and Daotanghe, respectively, but not in Maduo. At a given level of litter size, offspring size was similar between Delingha and Daotanghe.