Phylogeography Of Three Closely Related Tree Peonies Of Sect. Moutan

Tree peonies belong to Paeonia sect.Moutan?Paeonia.L?,which are characteristic of ornamental and economic value.The wild tree peonies provide important germplasm resources for development and cultivation of new varieties,and promote breeding cultivars with new flower colors,high resistance,and high oil production.Topographical changes and climatic fluctuation contribute profoundly to the distribution of wild species and its genetic structure.The valley derived from geologic changes not only impedes dispersal,but also provide corridors for species migration.Studies on genetic relationship of sect.Moutan have been broadly carried out.However,issues focused on phylogeography and evolutionary history remains still less known,especially for Paeonia decomposita Hand.-Mazz.,Paeonia rotundiloba?D.Y.Hong?D.Y.Hong,Paeonia rockii?S.G.Haw&Lauener?T.Hong&J.J.Li ex D.Y.Hong.Therefore,17 wild populations of three closely related tree peonies which were in all 228 individuals were sampled.Populations are located in dry-hot valleys of western Sichuan province and border area between Sichuan province and Gansu province.We collected the sequence information of ITS and two chlorplast gene?matK and ycf1?and analyzed the genetic structure and historical dynamic of three closely related tree peonies.Then ecological niche modeling will be carried out to predict past?Last Glacial Maximum,LGM?distributions area,the possible migration routes,and further to explore historical mechanism accounting for current distribution pattern.Our findings will provide a scientific basic for putting forward effective protection measures.Main conclusions are as follows:?1?111 haplotypes were identified according to ITS sequence variation?H1-H111?.The Maximun parsimony network,NeighborNet networks and phylogenetic trees based on ITS haplotypes all revealed three lineages?Lineage?-Lineage??.In the SAMOVA analysis,three groups were well defined.AMOVA analysis indicated that most of the variation could be attributed to variation within populations and less was partitioned between populations(F_ST=0.2099).At the overall samples level,h_T was estimated as 0.943,h_S as 0.776.A strong phylogeographical structure was revealed(N_ST=0.365>G_ST=0.178,P<0.01).In contrast,13 chlorotypes were recovered according to two concatenated cpDNA sequences?C1-C13?,and each species occupied private chlorotypes.The network analysis was consistent with the phylogenetic results,and four lineages were supported?Lineage A-Lineage D?.Genetic variation occurred mainly among populations,and at the overall samples level,the grouping level,significant genetic differentiation were observed among populations and among groups(F_ST>0.90).The total haplotypes diversity was higher?h_T=0.835?,while haplotypes diversity within populations was lower?h_S=0.143?.The genetic differentiation index of chloroplasts also revealed significant phylogeographical structure(N_ST=0.927>G_ST=0.829,P<0.01).?2?At the overall level,the data of ITS and cpDNA both did not deviate from neutrality,and the mismatch analysis also rejected the null hypothesis of spatial expansion.The analysis of BSP based on ITS indicated that the effective population size increased slightly from the middle to late Miocene period.The BSP analysis based on cpDNA showed that the population size has remained stable during the mid-Pleistocene.Overall,the population dynamics over history have rejected the occurrence of historical expansion or contraction events.?3?The results of the ecological niche modeling revealed that the three wild species of Sect.Moutan were located in the south of the current distribution area during the LGM period,and the distribution area of the three wild species in the LGM period overlapped greatly.When the major lineages of ITS and cpDNA data began to split,the Hengduan Mountain range had started gradually to uplift.Therefore,we speculated that the mountain uplift promoted the differentiation of the tree peonies ancestry lineage,and then,along with the climate fluctuation during the LGM period,the tree peonies migrated southwards along the valleys.When they migrated to the areas where were in present-day Chengdu Plain,tree peonies encountered,and subsequently hybridization occurred,leading to the lineages fusion.In summary,the results of this study revealed that wild populations of the three closely related tree peonies were rich in genetic resources.Topographical changes and climate fluctuations explained the distribution structure,and climate fluctuations are the main factors that triggered the lineages fusion.This study laid a theoretical foundation for the cultivation of new varieties and the protection of wild genetic resources.