中国枫香树遗传多样性及谱系地理研究

发布时间：2018-08-27 07:38

【摘要】：枫香树(Liquidambar formosana Hance)作为亚热带分布较广的第三纪孑遗树种,进化历史久远。在全球气候变化背景下,孑遗树种成为生物多样性保护研究的热点之一。开展枫香树群体遗传学与谱系地理学的研究对于解析其遗传结构,阐明其起源演化规律,探讨其现今分布格局特点与成因具有重要意义,研究结果不仅可以为枫香树遗传资源保护策略的制定提供科学依据,而且有利于枫香树遗传资源的科学管理与可持续利用和开发。本研究利用SSR分子标记、cpDNA非编码序列研究了枫香树在天然分布范围内的遗传多样性和谱系地理结构以及种群历史动态,同时,基于现有地理分布数据与气候数据,利用Biomod2物种分布模型重建不同时期的分布地理格局。取得的主要结果如下:(1)本研究从枫香树80 482条Unigenes中挖掘出10 645个潜在的SSR标记位点,平均每5.28 kb就能发现1个SSR位点,发生频率为13.22%,转录组中SSR的主要重复类型为二核苷酸重复。基于转录组数据共开发了14对多态性SSR引物;随后,利用这些引物对湖北红安(HA)群体进行群体取样策略研究,结果表明枫香树群体遗传分析的最小取样数量应为17-26个单株,单株采样间距需大于50 m。(2)从14个SSR位点中筛选了11个位点,对枫香树的25个群体691个个体进行遗传多样性研究。11个位点共检测到67个等位基因,平均观测等位基因数(Na)为6.0909,平均有效等位基因(Ne)的数量为1.9266,平均Shannon信息指数(I)为0.8178,平均观测杂合度(Ho)和期望杂合度(He)分别为0.4090和0.4322。枫香树具有中等水平的遗传多样性(He=0.399),其中贵州兴义(XY)群体具有最高的遗传多样性(He=0.469)。通过地区水平的遗传多样性对比,西南地区的秦巴和贵州群体表现出最高的遗传多样性(He=0.435),其次是大别山以及周围的丘陵地区和沿海地区,然而,中部地区表现出最低的遗传多样性和杂合子缺失。结果表明中国西南地区是枫香树遗传多样性丰富的热点地区,边缘群体较低的遗传多样性可能由于地理隔离或者奠基者效应引起的。枫香树群体有中等水平的遗传分化(Fst=0.0757),而且Mantel检验表明群体遗传变异与群体地理距离不存在显著相关性(P0.05),这表明地理隔离不是造成枫香树中等遗传分化的主要原因。群体遗传分析表明枫香树的遗传变异主要存在于群体内部的个体之间,因此优树选择将成为利用天然变异进行遗传改良的有效方法之一。UPGMA聚类结果表明25个群体被分成三大类群,与主成分分析(PCoA)和Structure结果完全一致。(3)采用4个叶绿体间隔区片段(cpDNA)对枫香树25个群体的251个个体进行测序,基于整合的2 732 bp比对数据,一共检测到20个多态性位点,得到20种单倍型,其中10个单倍型为某一群体所特有,18个群体具有1种以上的单倍型。枫香树物种具有较高的叶绿体遗传变异(Ht=0.909±0.0192),然而群体内的平均遗传多样性较低(Hs=0.323±0.0553)。单倍型的变异主要发生在群体间(Fst=0.73012),群体内遗传多样性低或许是由于受限制的基因流(Nm=0.18)造成的。总的单倍型多态性Hd为0.88762,总的核苷酸多态性π为0.00144,其中广西凭祥(PX)群体具有最高的单倍型多态性(Hd=0.75556),具有5种单倍型;福建建瓯(JO)群体具有最高的核苷酸多态性(π=0.00120)。群体遗传分化系数(Nst(0.730)Gst(0.645),P0.05),表明枫香树群体存在显著的谱系地理结构。分子方差分析(AMOVA)结果显示,大部分叶绿体遗传变异存在于枫香树群体间(75.34%),明显高于群体内的遗传变异(24.66%)。Mantel检验表明枫香树群体间不存在地理隔离现象(P0.05),中性检验和失配分析表明枫香树群体在历史上经历过扩张事件。单倍型H4出现的频率最高(50/251),其次为H1(42/251)和H5(32/251),具有这三种单倍型的个体占总数的49.4%(124/251),H4和H1是分布最广泛的单倍型。H5单倍型位于网络图的中心位置,是最古老的单倍型。基于群体遗传与单倍型分析结果,表明枫香树可能存在多个避难所,如西南地区的广西凭祥(PX)、贵州兴义(XY),东部地区的安徽黄山(HSAH)、福建建瓯(JO)很可能是枫香树的比较重要的避难所。采用宽松分子钟计算的枫香树现存群体的共祖时间是在10.30 MYA百万年前(95%HPD:9.74-15.28),属于第三纪的中晚期,分化的原因是第三纪的地质和气候事件。(4)利用Biomod2集合10个物种分布模型重建了枫香树不同历史时期的地理分布格局,结果显示枫香树的最适分布区与其现有分布区相吻合,表明枫香树的分布已经达到其最大的分布范围。对过去历史时期(LIG、LGM)的潜在地理分布进行重建,说明枫香树存在“盛冰期扩张,间冰期收缩”的现象。通过预测气候变化对未来物种分布区及其面积变化的比较,未来80年内,气候变化对枫香树的分布并没有显著影响,呈现相对稳定的状态。平均日较差和最冷季度平均温度是影响枫香树分布最重要的环境因子,表明限制其向北扩张的最重要的环境因素就是温度。
[Abstract]:Liquidambar formosana Hance has a long evolutionary history as a tertiary relic tree species widely distributed in subtropics. Under the background of global climate change, Liquidambar formosana Hance has become one of the hotspots in biodiversity conservation. It is of great significance to study the characteristics and causes of distribution pattern of Liquidambar formosana. The results not only provide a scientific basis for the formulation of conservation strategy of genetic resources of Liquidambar formosana, but also benefit for the scientific management and sustainable utilization and development of genetic resources of Liquidambar formosana. The genetic diversity, pedigree geographic structure and population dynamics of Liquidambar formosana in natural distribution were studied. Based on the existing geographic and climatic data, the distribution patterns of Liquidambar formosana in different periods were reconstructed by using Biomod2 species distribution model. The main results were as follows: (1) This study was conducted from 802 Unigenes of Liquidambar formosana. A total of 10 645 potential SSR marker loci were identified, with an average frequency of 13.22% per 5.28 kb. The main type of SSR duplication in transcriptome was dinucleotide duplication. A total of 14 pairs of polymorphic SSR primers were developed based on transcriptome data. The results showed that the minimum sampling number of Liquidambar formosana population should be 17-26 individuals, and the sampling interval should be more than 50 m. (2) 11 loci were selected from 14 SSR loci, and genetic diversity of 25 populations of Liquidambar formosana was studied. A total of 67 alleles were detected at 11 loci, and the average number of alleles (Na) was observed. The average number of effective alleles (Ne) was 1.9266, the average Shannon information index (I) was 0.8178, and the average observed heterozygosity (Ho) and expected heterozygosity (He) were 0.4090 and 0.4322, respectively. Liquidambar formosana had moderate level of genetic diversity (He = 0.399), among which the Xingyi (XY) population in Guizhou had the highest genetic diversity (He = 0.469). The genetic diversity of Qinba and Guizhou populations in southwest China was the highest (He=0.435), followed by the Dabie Mountains and surrounding hilly and coastal areas. However, the genetic diversity and heterozygote deletion were the lowest in central China. In hot spots with abundant diversity, low genetic diversity of marginal populations may be caused by geographic isolation or founder effect. There was moderate genetic differentiation in Liquidambar formosana population (Fst = 0.0757), and Mantel test showed that there was no significant correlation between population genetic variation and population geographic distance (P 0.05), indicating that geographic isolation did not exist. Population genetic analysis showed that genetic variation of Liquidambar formosana mainly existed among individuals within the population. Therefore, tree selection would be one of the effective methods for genetic improvement by natural variation. UPGMA clustering results showed that 25 populations were divided into three groups with principal components. The results of PCoA and Structurure were identical. (3) Two hundred and fifty-one individuals from 25 populations of Liquidambar formosana were sequenced by using four chloroplast spacer fragments (cpDNA). Based on the integrated 2 732 BP data, 20 polymorphic loci were detected and 20 haplotypes were obtained, 10 of which were specific to a certain population, and 18 populations had one of them. The haplotype of L. formosana was higher than that of L. formosana (Ht = 0.909 + 0.0192), but the average genetic diversity within the population was lower (Hs = 0.323 + 0.0553). The variation of haplotype mainly occurred among populations (Fst = 0.73012), and the low genetic diversity within populations was probably due to the limited gene flow (Nm = 0.18). The haplotype polymorphism Hd was 0.88762, and the total nucleotide polymorphism was 0.00144. Among them, Pingxiang (PX) population in Guangxi had the highest haplotype polymorphism (Hd = 0.75556) with five haplotypes, and Jian'ou (JO) population in Fujian had the highest nucleotide polymorphism (pi = 0.00120). Molecular analysis of variance (AMOVA) showed that most of the chloroplast genetic variations existed among Liquidambar formosana populations (75.34%) and were significantly higher than those within the population (24.66%). Mantel test showed that there was no geographic isolation among Liquidambar formosana populations (P 0.05), and neutral test and mismatch analysis showed that there was no geographic isolation among Liquidambar formosana populations. Haplotype H4 (50/251), followed by H1 (42/251) and H5 (32/251), accounted for 49.4% (124/251) of the total number of individuals with these three haplotypes, and H4 and H1 were the most widely distributed haplotypes. The results of haplotype analysis showed that there might be many refuges for Liquidambar formosana, such as Pingxiang in Guangxi (PX), Xingyi in Guizhou (XY), Huangshan in Anhui (HSAH) in the southwest, and Jian'ou in Fujian (JO) in the east. The common ancestor time of Liquidambar formosana population calculated by loose molecular clock was 10.30 MY. A million years ago (95% HPD: 9.74-15.28), it belonged to the middle and late Tertiary, and the reason of differentiation was the Tertiary geological and climatic events. (4) The geographical distribution pattern of Liquidambar formosana in different historical periods was reconstructed by using 10 species distribution models of Biomod2. The results showed that the optimal distribution area of Liquidambar formosana was consistent with its existing distribution area. The potential geographic distribution of Liquidambar formosana in the past (LIG, LGM) was reconstructed. The phenomenon of "full glacial expansion, interglacial contraction" was found in Liquidambar formosana. The average daily range and the average temperature in the coldest quarter are the most important environmental factors affecting the distribution of Liquidambar formosana, indicating that the most important environmental factor limiting its northward expansion is temperature.
【学位授予单位】：中国林业科学研究院
【学位级别】：博士
【学位授予年份】：2017
【分类号】：S792.99

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