Phylogeography Of Rhododendron Subg. Rhodorastrum

The study of phylogeography was of great significance to explain the present geographical distribution pattern of species,population genetic structure and the formation of diversity.In this study,four species（Rhododendron ledebourii Pojark.,R.dauricum L.,R.sichotense Pojark.,R.mucronulatum Turcz）which belonged to Rhododendron subg.Rhodorastrum（Maxim.）C.B.Clarke,Ericaceae were focused to analyze the population dynamics history of genetic structure,genetic diversity and genetic relationship based on 69 populations,total 401individuals.Meanwhile,the Maximum Entropy Model was used to simulate the geographical distribution patterns of R.ledebourii and R.sihotense under the last interglacial,last glacial maximum,current and future scenarios,and explore the dominant factors restricting the geographical distribution pattern.The main findings were as follows:（1）Based on four chloroplast gene fragments（Tab AB,Tab CD,mat K,psb C-trn S）,a total of 27 haplotypes were detected in 69 populations of this subgenus and showed a high genetic diversity（H_T=0.856）.Three branchs were divided by the phylogenetic tree based on chloroplast fragments.The first branch included 6 kinds of haplotypes belonged to R.ledebourii（Group1）;The second branch included four haplotypes which located from central Siberian plateau to the Greater Khingan Mountains and Lesser Khingan Mountains region belonged to R.dauricum（Group2）;The third branch included 17 kinds of haplotypes belonged to R.sichotense,R.mucronulatum and R.dauricum located in Changbai Mountains（Group3）.The result of STRUCTURE analysis and the result of TCS haplotypes network graph were consistent with the result of phylogenetic tree.（2）Rhododendron subg.Rhodorastrum had a significant geographical structure(N_ST>G_ST,p<0.05);The geographical isolation（IBD）analysis showed that the genetic distance was correlated with geographyical distance in this subgenus.The neutrality test and mismatch distribution analysis at the subgenus level showed the subgenus did not experience large-scale expansion events in history.Genetic differentiation of the four species mainly occured between populations.BEAST estimated the common ancestor of the Rhododendron subg.Rhodorastrum divergenced around 18.96 Mya.The common ancestor was distributed in North Asia-Sikhoite Mountains.（3）The Maximum Entropy Models was used to simulate the geographical distribution patterns of Rhododendron subg.Rhodorastrum.The results showed that R.ledebourii showed a trend of interglacial contraction and glacial expansion,and the dominant factors were altitude and average temperature in the driest season.R.sihotense showed a trend of expansion in interglacial period and contraction in maximum glacial period.The dominant factor was precipitation in the warmest season.In three future scenarios,the geographical distribution of R.ledebourii was likely to be further reduced,and the reduction would increase with the increasing of greenhouse gas emission;The geographical distribution of R.sichotense would shrink slightly under RCP2.6 and increase under the other two scenarios.In this study,the genetic structure,genetic diversity,biological geographical structure,group dynamic history,geographical distribution pattern of the Rhododendron subg.Rhodorastrum were revealed.This study provided reference and scientific basis for in-depth understanding of the evolutionary history of Rhododendron subg.Rhodorastrum,theoretical basis for further study of the succession process of the distribution patterns of modern plant groups in East and North of Asia,and reference for the conservation of germplasm resources of this subgenus..