Altitudinal variation in life-history features of a Qinghai-Tibetan Plateau lizard

Environmental changes along an altitudinal gradient can facilitate the differentiation of life-history features in ectothermic species,but little attention has been devoted to the reciprocal influence of altitude and alpine slope directionality on life-history variation.According to life-history theory,increased environmental stress causes a change in reproductive allocation from number to quality of offspring,as well as a stronger trade-off between size and number of offspring.To clarify the influence of environmental pressures on the life-history features of the Qinghai toad-headed lizard Phrynocephalus vlangalii along an altitudinal cline,we surveyed late pregnant females from 3 populations of low(2,600 m),middle(3,400 m),and high(3,600 m)elevations in the Dangjin Mountain of Gansu,China from July to October 2019,and compared their inter-population differences in maternal body size,reproductive characteristics,offspring growth,and locomotor performance.Because of lower temperatures,higher humidity,and lower light intensity caused by slope aspect and altitude,the middle-altitude region experienced stronger environmental stress than the high-and low-altitude regions.Our results showed that females were larger at middle-and high-altitude sites and smaller at the low-altitude site,following Bergmann’s rule.We also found that females from low-altitude population gave birth earlier than those from the middle and high altitudes.Our results showed a shift in the offspring size-number trade-off of P.vlangalii in response to colder and harsher environments,with lizards from the alpine steppe(i.e.the middle-and high-altitude habitats)producing fewer but larger offspring than those from the warm steppe(i.e.the low-altitude habitat).Low-altitude juveniles grew faster than high-altitude ones,but at the same rates as middle-altitude juveniles.This result demonstrates that the growth of P.vlangalii was associated with temperature and light intensity.Our findings contribute to enhancing our understanding of the altitudinal variation in life-history features of plateau ectotherms and their phenotypic plasticity or local adaptation.