The Variation And Phylogeography Of Cerasus Serrulata Mill.Populations

Cerasus serrulata(Lindley)Loudon,is an important germplasm resource of flowering cherry for ornamental purpose.It has widely distributed in central-western regions and eastern part of China,as well as the Korean peninsula and Japan perhaps.Population variations and the phylogenetic relationships with the sibling species'definition of C.serrulata were still controversial,due to its broad distribution,huge variability and disagreement in taxonomic view.This article took wild populations of C.serrulata and sibling species(complex)as the research objects,combining methods of both morphological and molecular markers for systematic study.The degree of population variation and differentiation of C.serrulata,and the relationship with sibling species were then both discussed and redefined,an sufficient evidence of classification were therefore formed.The evolutionary relationships of phylogeography in different regions of C.serrulata's populations were also integrated,in order to further discuss its spatial and temporal pattern in genetic variations,clarifying affects to genetic variation,differentiation,evolution and distribution by genetic drift and differentiation as well as natural environmental factors.The main results of this study are listed as follows:(1)Variation of C.serrulata and taxonomic treatmentC.serrulata distinguishes with other groups of Cerasus from the characters of synchronous in blooming and leaf unfolding,margin acuminately serrate or biserrate,hypanthium long-tubular,sepal erect as well as drupe purplish black,etc.Different populations of C.serrulata showed much complicated variance in phenotypic character,including obvious traits in tree form,bud,young leaf color,flower color,speal and indumentum,etc,as its extensive geographical distribution and strong adaptability.According to the results of morphological markers,the taxonomic viewpoint that Subgenus Microcerasus and Subgenus Cerasus were divided from the genus Cerasus based on tree form and three buds remains controversial.Populations of Subgenus Cerasus in alpine habitats are similar to Subgenus Microcerasus from phenotypic traits.In the character observation and statistical analysis of C.serrulata and sibling species(complex),various populations of C.serrulata were able to distinguish from complex groups according to important identifying traits.Meanwhile,there were some important traits also co-exist among a similar groups,which was consistent with existing classification dispute of C.serrulata complex.The results combined both morphological and molecular markers showed that The Indumentum characteristics from different populations were continuous variation in complex of C.serrulata.We therefore support C.serrulata var.pubescens should mingled with C.serrulata;Combining multiple traits of continuously variation,support C.laoshanensis mingled with C.serrulata;The C.xueluoensis is much closer to C.serrulata than Subgenus Microcerasus,hence support the establishment of the new species of C.xueluoensis,which is belong to Subgenus Cerasus in taxonomy system;The population HGS is consequently treated as a new variety C.serrulata var.huanggangensis;The C.jamasakura,C.sargentiia,C.speciosa and C.lannesiana should treated as distinct species in taxonomic treatment are also supported.(2)Population genetic diversity and genetic structureGenetic diversity and genetic structure of C.serrulata were analysed from 18 populations and 327 individuals using 17 SSR primers.The results indicated that the populations of C.serrulata have high genetic diversity level at the species level,populations from west and part of the southeast show high genetic diversity.The genetic differentiation analysis showed that high levels of genetic differentiation were existed among the populations and within the populations.According to the STRUCTURE analysis,for K=7,total 18 populations of C.serrulata were divided into three groupings:?cluster(north-west group),consisting of MP,BTM and LIS;?cluster(south-west group),consisting of He S and CPL;TTZ,BHS,NS,HS,HGS,TMS,LS,TS,MS,YTS,Lao S,FHS and K-NS were gathered as?cluster(east group);For K=4,the STRUCTURE analysis indicating genetic material of 18 populations of C.serrulata came from 4 gene pool clusters.Gene communication and introgression among groups were complicated,meanwhile,the north-west group showed similar genetic structure as the north-east group.Sequence analysis of 18 populations of C.serrulata was conducted based on 3 cpDNA fragments(mat K,trn D-E,trn S-G).Total of 19 haplotypes were identified from all populations,the total haplotype diversity(H_T)and nucleotide diversity(?=Pi×10^-3)were 0.828 and 1.490,respectively.The C.serrulata shows high H_T level,which exceed the statistical average 0.67,this might related to the wide geographical distribution of C.serrulata.Whereas within-population diversity(H_S)was detected lower to 0.387,indicating that the genetic diversity occurs mainly among populations;A relative high genetic differentiation(F_ST=0.693),suggesting that genetic differentiation was highly occurred among populations of C.serrulata;A significant phylogeography structure was observed(Nst=0.388>Gst=0.328,P<0.05).Abundant common haplotypes were detected from haplotypes distribution network,infering that haplotype frequencies occurred comparatively even at populations from same geographic group,strong introgression and little differentiation were observed among populations.Genetic diversity and differentiation of ITS was consistent with cpDNA,reflecting that high genetic variation of C.serrulata at species level due to widely distribution and long time evolution.All in all,high genetic variation of C.serrulata at species level due to widely distribution and long time evolution.The genetic diversity from different populations was great difference,but average is lower;There were certain but not strong differentiations occured among populations of C.serrulata,frequent exchange and introgression were also existed?(3)Phylogeographic structure and population dynamic historyThe results of phylogenetic tree and TCS network based on cpDNA haplotypes showed that 2 major lineages were differentiated(with 4 geographical groups)from populations of C.serrulata:north-west lineage[NW]+((south-east lineage[SE],north-east[NE]),south-west[SW]).The phylogeographic structure basically the same as cluster result of TCS network based on haplotypes.The molecular clock was estimated the phylogeographic differentiation due to geographic isolation in the late Miocene(10.60 mya(PP=1;95%HPD:8.83-12.46mya).Since Miocene was interglacial period between secondary and third glacial period(250-2mya),which was during the period of westward orogeny,with climate mild and humid;The Qinghai-tibet plateau,Yungui plateau and Qinling mountain were intensely uplifted by the influence of the Himalayan movement.Those geological vigorous movements might cause north and south geographic segregation and differentiation in western regions of C.serrulata.Another lineage,namely((south-east lineage[SE],north-east[NE]),south-west[SW])geographical groups,can be speculated originated from the southwest region(SW&SE);SW achieved phylogeographic differention from NE in Pliocene(3.93 mya);Other secondary branches were mainly differentiated in Pliocene and Pleistocene?The results of neutrality test(NT)and mismatch distribution analysis(MDA)were not exactly the same.The MDA revealed4 geographical groups and all populations of C.serrulata fitted the expectation of space expansion model.The results of haplotype distribution,diversity analysis and TCS network all showed the south-western region was most likely to be a refuge for C.serrulata;South-east region might be another refuge after integrated with the analysis of MDA.Based on combination of molecular clock,MDA and TCS network,we can infer that south-west China experienced two independent colonization,including north-westward and eastward in 0.719mya(95%CI:0.022-1.452 mya);The populations of C.serrulata from south-east of China(HS,LS,TMS.etc)experienced northward expansion in the period around 0.665 mya(95%CI:0.000-1.249 mya).As population demographic expansion of C.serrulata mainly occurred in the middle of the Pleistocene,which belong to the geological period of the third glacial period(Quaternary glaciations),we therefore speculate during the quaternary glaciations,climatic variations by multiple interglacial periods the promoted the expansion of C.serrulata.Its natural distributions located in the south-west and south-eastern high mountains as well as cool humid areas in the north-east China,which can be also well explained in terms of habitat and climatic characteristics of the distribution areas.Therefore,C.serrulata formed its distribution center and refuges(SW&SE)before the quaternary glaciations,then during the interglacial period of it,C.serrulata diffused from south-west to north-west(Shanxi Provience)and south-west China(LS,HS,TMS,etc.);After that,it experienced a north-eastward expansion centred on the south-east region(YTS of Jiangsu Provience,TS and LS of Shandong Provience,Liaodong peninsula and the Korean peninsula).The results of ribosomal distribution,TCS network and phylogenetic tree based on analysis of ITS nuclear gene were not consistent with that of cpDNA analyses.The results of SSR were combined and analyzed,we can speculate the north lineage of C.serrulata was existed,where experienced the dispersion and migration from north-west region(NW)to north-east regions(FHS)and Korea(NE).In conclusion.Combining the phenotypic and molecular evidence,the variation and its classification processing with relatives tend to be more reasonable.Certain but not strong differentiations occured among populations of C.serrulata,frequent exchange and introgression were also existed.High genetic diversity and distinct geographical structure were detected at species level.In the late Miocene two major lineages were differentiated due to geographic isolation cause by western orogenic movements.C.serrulata formed its distribution center and refuges before the quaternary glaciations,and then diffused from south-west to north-west and south-west China.After that,it experienced a north-eastward expansion centred on the south-east region;It speculated that C.serrulata experienced the routes of dispersion and migration from north-west region to north-east regions and Korea.In this study,the population variation and phylogeographic structure of C.serrulata has been revealed,these results will contribute to the classification of its populations and sibling species as well as providing an theoretical basis for the protection and utilization of germplasm resources.