Phylogeography And Genetic Diversity Of Quercus Baronii And Quercus Dolicholepis Populations

Quercus baronii and Quercus dolicholepis,are two deciduous trees and belong to Fagaceae.Quercus and Section Echinolepides.Both species are endemic to China and mainly distributed in the Qinling-Daba mountains area with important economic and irreplaceable ecological values.These two species are located in sympatric or parapatric areas,which are ideal experimental materials for studying the sympatric or parapatric speciation and comparative phylogeography.In this study,33 natural populations of of Q.baronii and Q.dolicholepis were collected by using chloroplast DNA(cpDNA)and microsatellite(nSSR)for the first time(20 populations for Q.baronii and 13 populations for Q.dolicholepis).By comparing the phylogeographic structure and genetic diversity of the two closely related species lineages will help us to infer whether the biodiversity in Qinba region was effected by the environmental changes or the climate oscillations in the evolutionary.The main findings are as follows:(1)Q.baronii and Q.dolicholepis(33 wild populations)with 314 individuals were analysed based on four cpDNA(matK,ycfl,rps16-trnQ,psbA-trnH).The results showed that the genetic diversity of chloroplast DNA was relatively high at the population level,and the haplotype polymorphism(Hd)of Q.baronii was 0.914 lower than that of Q.dolicholepis(Hd=0.987),while the nucleotide polymorphism of Q.baronii(Pi = 0.0021)was lower than that of Q.dolicholepis(Pi = 0.0031).Total of 24 haplotypes(H1-H24)were detected by DnaSP 5.1 software.Among them,H1 was shared by Q.baronii and Q.dolicholepis as the most abundant haplotype.Additionally,a total of six haplotypes(H5-7,H9,H11 H13)is unique for Q.baronii group and 6 haplotypes(H12,H17,H20,H22,H23 and H24)were unique to the populations of Q.dolicholepis.The results of molecular variation analysis of variance(AMOVA)showed that there was a high genetic difference between the two species FST=0.969,and the genetic differentiation among the populations was also significant,including FST= 0.995 and FST=0.953.The results of Mantel test showed that there was no correlation between geographical distance and genetic distance between Q.baronii and Q.dolicholepis(R =-0.890,P = 0.490,Group:R =-0.084,P = 0.270,R<0 and P>0.05).Gene flow between populations was not significantly affected by geographical distance.NETWORK analysis and haplotype geographic distribution showed that high genetic diversity and unique haplotype was detected from the Qinling-Bashan populations.we speculated these regions might be glacial refuge for these two species.After the glacial period,there was no large-scale expansion for the two closely related species.(2)Based on ten nSSR molecular markers,the genetic diversity and genetic structure of 565 individuals of 33 wild populations of Q.baronii and Q.dolicholepis were analyzed.The results showed high genetic diversity for Q.baronii and Q.dolicholepis(P = 96.5%,PPL =89.5%),but it is lower than that of widely distributed Quercus.The results of molecular variation analysis showed that the genetic variation of Q.baronii and Q.dolicholepis were mainly detected in the populations,accounting for 78.37%,and the genetic differentiation coefficient FST was 0.216.(Including 87.22%variation in population,12.78%in population,90.80%in group and 9.20%in population).In addition,based on the results of Bayesian clustering analysis,the optimal grouping was 2,and the populations of Q.baronii and Q.dolicholepis were clustered into two groups:one of which was mainly distributed along the Qinling Mountains and the other was mainly distributed along the Daba Mountain.The Rich genetic diversity and low level of genetic differentiation may be associated with the complex life history characteristics and evolution of dynamic history,also with the Qinba mountain special geographical environment.