Phylogeography Of Hippophae Rhamnoides Ssp.Sinensis

Phylogeography, a field of study concerned with the principles and processesgoverning the geographic distributions of genealogical lineages. The uplift of theQinghai-Tibetan Plateau （QTP） and Quaternary climate changes are crucial aspectsaffecting the distribution of the plateau biota. QTP is the center of origin of the H.rhamnoides. Hippophae rhamnoides ssp. sinensis, a subspcies of H. rhamnoidesendemic to China, is a dioecious, outcrossing plant. it is the most widely distributedseabukthurn in China. The mainly distributions of this taxon’s location in28。-44。N,93。-122。E and at the elevation between550-3000m. At present, the formation patternof H. rhamnoides ssp. sinensis’ s modern geographical distribution and its glacialrefuge remains unclear. In this thesis, the phylogeography of H. rhamnoides ssp.sinensiswe was studied based on the population genetic marker of the DNA sequence,arming to clarify its possible refuge and migration routes in the Quaternary glacialand analyze the causes of modern geographical distribution of H. rhamnoides ssp.sinensis. The main results and conclusions are as follows:1)322individuals from20populations of the H. rhamnoides ssp. sinensis as wellas individuals from the out-group species H. rhamnoides subsp. yunnanensisand H. neurocarpa （one individual respectively）were collected, and thematernally inherited chloroplast （cp） DNA fragments （trnT-trnL） weresequenced. The length of trnT-trnL fragment of H. rhamnoides ssp. sinensis is1208bp, containing six polymorphic sites, of which five were parsimony-informative sites, with38insertion-deletion. We identified a total of21haplotypes. For its highest frequency and widest distribution among thesehaplotypes, the Hap4is the ancient haplotype and mainly distributed in thenortheastern margin of the Qinghai-Tibet Plateau in S25, S27and S28and theLoess Plateau in S3, S5, S8, S16, S17, S18and S20populations. There are15private haplotypes distributed at the northeast edge part of the Tibetan Plateaupopulations. H. rhamnoides ssp. sinensis have high level of haplotype diversity（HE=0.87） and nucleotide diversity （π=0.0029）;2) The populations at the northeast edge of the Qinghai-Tibet Plateau is mainlycomposed of15private haplotypes, significantly different from the composition of haplotype of the Loess Plateau populations, which caused high geneticdifferentiation of H. rhamnoides ssp. sinensis（GST=0.612）. That means geneticvariation mainly exists among populations. Analysis of the phylogeographicstructure of H. rhamnoides ssp. sinensis showed that Nst=GST, which meansthere is no significant phylogeographic structure in the distribution range of H.rhamnoides ssp. sinensis, meanwhile there are extensive genetic exchangesamong populations.3) In this paper, two different mutation rates, i.e.4.87×10^-10s/s/y and2.0×10^-9s/s/y were used to estimate the haplotypes divergence time of H. rhamnoidesssp. sinensis. The results were3.87×10⁵years and0.941×10⁵years,respectively. Both these dates across the Pliocene and Quaternary medium term,indicating that H. rhamnoides ssp. sinensis has experienced dramatic globalclimate changes at the Quaternary Ice Age, and the time of haplotypesdifferentiation was about38.7-9.41thousand yr ago.4) According to the location of the ancient haplotypes and private haplotypes, weidentified Weiyuan, Lintan of Gansu, Menyuan, Guide of Qinghai or theneighborhood areas as the refugice of H. rhamnoides ssp. sinensis at theQuaternary Ice Age. The results of mismatch distribution analysis and neutralitytest analysis （Tajima’s D and Fu’s FS） all supported that large-scale expansionoccurred among the populations of H. rhamnoides ssp. sinensis after theQuaternary Ice Age. And constrained by the limiting factors such as light,temperature and precipitation, H. rhamnoides ssp.sinensis were gradually alongthe eastern and northeastern fringes of Qinghai-Tibet Plateau, arossing theLoess Plateau, arriving southwest corner of the Great Khingan, forming themodern distribution pattern of H. rhamnoides ssp. sinensis.