Sexual Dimorphism And Geographic Variations Of Morphological Characteristics Of Phrynocephalus Axillaris

Sexual dimorphism(SD)is common phenomenon among reptiles,which is an adaptive result caused by asymmetric selection pressures on male and female.The comprehensive researches on sexual dimorphism of different reptiles were launched.However,similar research on lizards in arid area,even in desert is relatively limited.The Yarkand toad-headed agama,Phrynocephalus axillaris,is a small-sized lizard of the genus Phrynocephalus in China,which is endemically distributed in the desert and semi-desert areas in Tarim Basin,Turpan-Hami Basin and Dunhuang Basin.In this study,307 adults of P.axillaris(158 males and 149 females)were sampled from five different populations in Tarim Basin.Eight external morphological characteristics,including snout-vent length(SVL),head length(HL),head width(HD),head height(HH),interorbital distance(ID),mouth width(MW),abd?m?n l?ngth(AL),and tail length(TL)were measured.Statistical analysis were employed to explore the possible pattern of sexual dimorphism,geographic variations of morphological characteristics,as well as the relative driving reasons of P.axillaris in five populations.These would enrich our understanding on adaptive changes of widespread reptile,such as P.axillaris yielded from the process of adapting different environments.The main results are summarized as follow:1.There was a marked larger mean snout-vent length in male than in female of P.axillaris among five geographic populations.The pattern of male-biased sexual dimorphism in P.axillaris could be explained by the effect of sexual selection pressure on male.2.Besides the snout-vent length,other morphological characteristics of P.axillaris also showed sexual dimorphism.The number of morphological characteristics with sexual dimorphism in different populations was different,which indicated that P.axillaris distributed in different geographic environments might encounter the different kind and different level of selection pressures.In addition,the different direction shown on the abdomen length in sexual dimorphism among five populations would be yielded from the different intension of the fecundity selection pressure on female in five populations.3.There was allometric growth of morphological characteristics between both sexes of P.axillaris in each geographical population,but the number of morphological characteristics with allometric growth and their degree were variable in different populations.These might be caused by the differences in selection pressure,growth rate and population density of both sexes in different geographic populations.4.There were significant geographical differences in the sexual size dimorphism of P.axillaris among five populations.And the variation characteristics of sexual dimorphism among populations followed Rensch's law,that was,the degree of sexual dimorphism increased with the growth of body size in male.5.There were obvious geographical differences in body size and morphological characteristics of P.axillaris.The sequence of mean snout-vent length in both sexes was as follows: southwestern population > western population > southeast population > northern population > eastern population.The variation trend of body size in five populations showed an inverse Bergmann's law.That was the body size of P.axillaris increased with the decrease of latitude.But the variation of other morphological characteristics among populations did not present some trend regularly.According to the degree of differences in morphological characteristics among different geographical populations,five geographic populations of P.axillaris could be approximately divided into two groups,the western and southwestern populations could be regarded as one group,and the other three populations could be regarded as another group induced by the obvious geographic variations in morphological characteristics.Geographic variations of morphological Characteristics in P.axillaris could be related with the differences in environmental factors,such as latitude,recipitation and temperature,the selection pressure and population density in each local population.