Sexual Dimorphism And Geographic Variation Of The White-lipped Pit Viper(Trimeresurus Albolabris)

Sexual dimorphism refers to the phenomenon of differences between male and female individuals in asexternal morphological characteristics such as body size,body surface color,as well as behavioral characteristics,physiological structure and life history.Geographic variation refers to species with a wide geographical distribution range.Due to selection pressure,the population inhainating in different spatial regions usually has significant variation in physiology,morphological characteristics and population behavior patterns associated with biogeospatial distribution.At present,most studies are focused on lizards and amphibians,but there are relatively few studies on sexual dimorphism and geographic variation of snakes due to their secretive behavior,the venomous nature of most species,and the difficulty in obtaining samples.In order to understand how animals adapt to the environment,it is important to study the widely distributed species.Trimeresurus albolabaris(Gray,1842)is one of the most common venomous snakes belonging to Squamata,Viperidae and Crotalinae.Trimeresurus albolabaris is widely distributed in China,Thailand,Laos,Cambodia,Vietnam,India,Bangladesh,Myanmar and other regions.In China,the distribution of Trimeresurus albolabaris is mainly concentrated in Hong Kong,Guangdong,Guangxi,Guizhou,Yunnan and other places.This species is one of the most widely distributed species in the genus Trimeresurus,and there are great differences in morphology between males and females.Therefore,it is an ideal model species for studying sexual dimorphism and geographical variation.In this research,we tested 99 samples of Trimeresurus albolabaris(female 57,male 42)from Guangdong,Guangxi,Fujian,Yunnan,Guizhou,Hong Kong and Hainan Islands of China to measure the length characteristics and the number of scales.Analysis of variance,analysis of covariance,allometric growth,index of sexual dimorphism,regression analysis,principal component analysis and other methods were used to make comparative studies.The main results in this paper were as follows:Compared with male,female have longer Snout-vent length,wider anal scales and larger head size.The change position of female tail scale is closer to cloaca than that of male.Male have longer tails and more subcaudal scales than female.The morphological characteristics of sexual dimorphism include: Distance between supraocular scales and middle of rostral scales(SUTS,F = 8.79,P = 0.004),Head width(HW,F = 11.38,P = 0.001),Length of mouth(MOTS,F = 21.03,P < 0.001),Width of anal scales(VW,F = 6.92,P = 0.01),Distance between lateral supraocular scales(SUTSU,F = 7.64,P = 0.007),Tail length(TL,F =135.95,P < 0.001),Head length(HL,F = 37.68,P < 0.001)Distance between eyes and nostrils(ETN,F = 8.65,P = 0.004),Snout-vent length(SVL,F = 5.22,P = 0.025),Number of subcaudal scales(VENT,F =209.41,P < 0.001),Left subcaudal scales position of reduction from scale rows 8 to 6(SCL8to6,F = 67.56,P < 0.001),Right subcaudal scales position of reduction from scale rows 8 to 6(SCR8to6,F = 78.14,P <0.001),Left subcaudal scales position of reduction from scale rows 6 to 4(SCL6to4,F = 81.79,P < 0.001),and Right subcaudal scales position of reduction from scale rows 6 to 4(SCR6to4,F = 82.78,P < 0.001).There was no significant geographical variation in the Chinese population morphology of Trimeresurus albolabaris,but the degree of sexual dimorphism difference in the change position of tail scales is related to mean temperature of coldest quarter.Physical barriers,similar climate types,human activities,and other biological factors may lead to the absence of significant geographical variation in its morphology.In addition,the evolution speed of genes is relatively fast,and the differences in morphological characteristics may not be fully displayed in time.Biogeographical studies showed that Chinese populations were distributed in the two most distant genetic relationship geographical population branches,but the results of this paper show that there is no obvious geographical variation in the morphology of the Chinese population,and we speculate that there is no obvious geographical variation in the morphology of Trimeresurus albolabaris in Southeast Asia.