A Revisit To The Population Genetic Structure And Phylogeography Of The Plant Genus Dipteronia Oliv. (Aceraceae)

The genus Dipteronia Oliv.(Aceraceae),endemic to China,consists of two species, D.sinensis Oliv.and D.dyerana Henry.Both species are rare and endangered,are only found in the Qinling Mountains,Hengduan Mountains and Yunnan-Kweichow Plateau in China,and have only small and sparsely distributed populations with limited individual numbers.Therefore,they have been listed as Chinese Rare and Endangered Plant Species.Dipteronia is one of the woody relic genera in the floristic region of the northern temperate zone.The fossil record shows that species of this genus were once distributed in China(late Eocene)and North America(from the late Paleocene to the early Oligocene)in the Tertiary(Amy and Steven 2001;WGCPC 1978;Manchester 1999).Based on AFLP markers,cpSSR markers,and the sequences of several chloroplast non-coding regions(trnL-trnF,trnD-trnT,rps12-rpL20,rps16 intron),the aims of this study are:to characterize genetic structure and intra-species genetic diversity of 17 populations within D.sinensis and 4 populations within D.dyerana,as well as the relationship of genetic structure and geographical distribution among populations;to propose the corresponding protect strategies;to examine the type and diversity of chloroplast haplotypes within species and populations;to analyze the distribution of chloroplast haplotype and presume the possible ice age refuge of this genus;and to discuss the species evolution history and the inter-species differentiation.The main results of this study are as follows:1.The genetic diversity analysis found that both species had a high level of genetic diversity,and there were higher level of genetic diversity in species D.sinensis (AFLP:H=0.3319,Hsh=0.4880;cpSSR:H_T=0.9676)than in D.dyerana(AFLP: H=0.3047,Hsh=0.4450;cpSSR:H_T=0.9144).2.The genetic differentiation showed that there occurred a significantly high level of genetic differentiation between D.sinensis and D.dyerana(AFLP:F_ST=0.3904, p＜0.001;cpSSR:F_ST=0.4424,p＜0.001),Significantly high differentiation was also detected among populations within D.sinensis(AFLP:G_ST=0.3678,cpSSR: G_ST=0.8120)and within D.dyerana(AFLP:G_ST=0.3266,cpSSR:G_ST=0.7067), the gene flow between populations was limited,The Mantel test between the genetic distances and geographical distances suggested that high genetic differentiation among populations within D.sinensis and D.dyerana might be caused by geographical isolation.3.Based on the former study of molecular phylogenetic,Dipteronia species did not always form a clade,species D.dyerana was sometimes embedded within Acer species.It shows that there occurred a significantly high level of genetic differentiation between D.sinensis and D.dyerana,and D.dyerana was considered to evolve faster than D.sinensis.4.The comparative result of nuclear AFLP markers and chloroplast SSR markers generated in the present study are interpreted under the assumption of maternal inheritance of the chloroplast genome in Dipteronia.The gene flow ratios found low ratios of pollen flow to seed flow(5.4:1 in D.sinensis vs 3.0:1 in D.dyerana), thus,indicating that the gene flow in both D.sinensis and D.dyerana was mainly contributed by pollen rather than by seeds.5.No common chloroplast haplotype was observed between the species.The combined analysis with cpSSR and chloroplast non-coding gene sequences found that there were several disperse glacial refugia within species of Dipteronia,the main glacial refugia for species D.dyerana was its recent distribution southeastern-yunnan province,and with abroad distribution,the main glacial refugia of D.sinensis were Qinling mountains,Daba mountains,Funiu mountains, Wuling mountains and Shennongjia mountains.6.The population history dynamic analysis(Tajima's D=-1.045,P＞0.01,Fu and Li's D^*=-1.175,P＞0.01,Fu and Li's F^*=-1.316,P＞0.01)and chloroplast haplotype network(not like star)suggested that Dipteronia might not have obvious expansion during its evolutionary history,and inferred that the recent geographical distribution of this genus might be the distribution conservation of which in the last ice age.7.The main reason to make the Dipteronia plant endangered was destroying of its habitats.Because of cpSSR revealed that each population has its own haplotypes, and Dipteronia might not have obvious expansion during its evolutionary history, the main protect strategies are as follows:①To protect the habitat of each population to the greatest extent;②To protect the population which have high genetic diversity in order to maintain the high genetic variance;③To transplant individuals to the population with low genetic diversity from other natural populations in order to increase the genetic variance;④The in situ conservation as well as the ex situ conservation were all necessary for this genus protection.⑤The sampling strategies for ex situ conservation was sampling individuals from natural populations as much as possible,and by enlargement the exchange of seeds and young plants among populations,to make big population,great space,and create the chance for gene flow and gene recombine in order to preserve the most genetic variance to the greatest extent.