Phylogeography Of Iris Potaninii Maxim.

Dramatic changes in climate and environmental conditions during the Quaternary ice age have had profound and lasting effect on the current species distribution.Phylogeography provides new means to uncover the mechanism of biodiversity,genetic structure of population,spatial distribution pattern of current species,and stimulated a new line of life science.Iris potaninii Maxim.,belonging to genus Iris Linnaeus,Iridaceae,is a perennial herbaceous plant distributing in Gansu,Qinghai,Sichuan,Tibet,Inner Mongolia,and also occurring in Mongolia and Russia.I.potaninii is an important component of alpine grassland and alpine meadow on the Qinghai-Tibetan Plateau and its adjacent areas.In order to reveal the genetic diversity,phylogeographical pattern and population dynamic history of I.potaninii,we sequenced the chloroplast DNA region,and analyzed SSR loci of a total of 128 individuals from 15 populations collecting throughout the main distribution area of I.potaninii.In the cpDNA sequence matrix,there were 68 polymorphic information sites,and 19 haplotypes were detected.The haplotype diversity was 0.875 and the nucleotide diversity was 0.00417.At the species level,the genetic differentiation index was 0.92915,indicating that the genetic differentiation among populations was significant.The NJ tree constructed basing on the chloroplast sequence shows that,all I.potaninii individuals could be divided into 4 large branches: the population MZ from Hulun Buir Plateau constituted an independent branch;the population XJ from Hengduan Mountain,and the population KH from Southern Qinghai Plateau,constituted the second branch;and other I.potaninii populations distributing in Qinghai Tibet Plateau constituted the third and fourth branches.The haplotype networks indicated that the haplotypes between the population MZ and other populations distributing in Qinghai-Tibet Plateau showed obvious genetic differentiation.Except the population KH,all the other I.potaninii populations distributing in Qinghai-Tibet Plateau were closely related.Based on the Structure analysis,all populations of I.potaninii were divided into 4 clusters.AMOVA analysis result indicated that genetic differentiation of I.potaninii were found mainly among populations.In population dynamic historical analysis,the Tajima'D values of the populations DZ showed significant negative values,indicating that these populations may have occurred expansion events through the evolution history.The mismatch analysis of species levels showed that there could have not been any significant expansions through the evolution history of I.potaninii.9 SSR loci obtain 175 alleles in total.Each loci contained 19.4 alleles,the percentage of polymorphic loci(PPL)was 98.86%,and the genetic diversity value was 0.304,the average expected heterozygosity of population was 0.698,the average observed heterozygosity was 0.627,and the average inbreeding coefficient was 0.177,all the indexes above indicated that the I.potaninii had a high genetic diversity.The average index of genetic differentiation between paired populations was 0.17,which indicated no significant genetic differentiation among populations.Structure and PCA analysis were used to cluster 15 populations of I.potaninii,which can be divided into 4 groups.The results of AMOVA analysis showed that genetic differentiation of I.potaninii were found mainly within populations.The NJ tree based on SSR loci also supports 15 populations to be divided into 4 large branches.Based on all analysis results,this study indicated that the population MZ from Hulun Buir Plateau is an ancestral population;The Yushu area of Qingnan Plateau is the center of genetic diversity distribution.The changes of paleoclimatic conditions and the complex terrain of the Qinghai-Tibet Plateau and its adjacent regions shaped the current distribution pattern of I.potaninii,this paper explored this shaping effect to reveal the historical dynamics of the population of I.potaninii,identify its glacial refugia and possible post-ice period diffusion route.This study provides new scientific materials for the phylogeography studies of other plant in the Qinghai-Tibet Plateau and its adjacent areas,provides a scientific basis and reference for an in-depth understanding of the evolutionary history of genus Iris.