西川红景天分子系统地理学研究

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	西川红景天分子系统地理学研究
其他题名	Molecular Phylogeography of Rhodiola alsia (Crassulaceae)
	高庆波
学位类型	博士
导师	陈世龙
	2009-05-25
学位授予单位	中国科学院西北高原生物研究所
学位授予地点	西北高原生物研究所
关键词	西川红景天叶绿体dna片段冰期避难所分子系统地理学青藏高原
摘要	第四纪气候波动如何影响青藏高原地区植物的分布范围和居群遗传结构仍然不是很清楚。多数研究认为，第四纪冰期时高原台面上的居群退缩到高原东南部边缘的避难所内，间冰期或冰后期居群从避难所内重新扩散到高原台面地区。重扩散过程中的奠基者效应使得高原台面上的居群具有较低的遗传多样性。另外一些研究认为，某些耐寒的植物在第四纪冰期时并没有退缩到高原东南部边缘地区，而是在高原台面上的一个或几个避难所内保留下来。西川红景天Rhodiola alsia (Fröderström) S. H. Fu 隶属于景天科Crassulaceae红景天属Rhodiola L.，为青藏高原特有的多年生草本植物。该物种在青藏高原东南部边缘地区和高原台面均有分布，生于海拔3400-4800米的河漫滩、山坡石隙及流石坡地。本研究以西川红景天为研究对象，利用叶绿体DNA两个基因间隔区（trnS-trnG和rpl20-rps12）的序列数据，对西川红景天整个分布区内的18个居群（354个个体）进行分子系统地理学研究，揭示遗传变异在居群内和居群间的分布式样，并探讨该物种的冰期避难所及进化历史。主要结果如下： 1) 西川红景天cpDNA trnS-trnG基因间隔区共扩增成功239个个体，对位排列后序列长度为652bp，其中变异位点85处，变异位点百分率为13.04%，18个居群的平均核苷酸多样性为0.026453；rpl20-rps12基因间隔区共扩增成功315个个体，对位排列后序列长度为844bp，其中变异位点38处，变异位点百分率为4.50%，平均核苷酸多样性为0.005233。西川红景天trnS-trnG基因间隔区的变异位点百分率和平均核苷酸多样性均远高于rpl20-rps12基因间隔区，表明前者的进化速率快于后者。由于进化速率较快，trnS-trnG基因间隔区可以提供更多的信息位点，能更好的重建单倍型之间的系统发育关系。 2) 对西川红景天cpDNA trnS-trnG、rpl20-rps12基因间隔区及两套序列联合分析分别检测到23、31及45个单倍型。只有少数古老的单倍型（如trnS-trnG序列检测到的单倍型A2、A6、A7；rpl20-rps12序列检测到的单倍型H3、H5、H9及联合序列检测到的单倍型3和8）在居群中广泛分布，多数单倍型仅局限于一个居群或邻近的居群。青藏高原东南部边缘的居群（P12-P18）普遍具有较高的单倍型多样性（h）和（或）核苷酸多样性（π）并固定较多的特有单倍型，推测青藏高原东南部边缘地区是西川红景天在第四纪冰期重要的避难所。位于青藏高原台面最北部的居群（P1和P6）及最西部的居群（P8和P9）具有较高的单倍型多样性（h）和（或）核苷酸多样性（π），并被唐古拉山显著隔开，结合歧点分布分析和中性检验，推测第四纪冰期时西川红景天在高原台面上存在几个相互隔离的避难所。 3) 对西川红景天两个cpDNA基因间隔区序列联合分析发现，总的遗传多样性很高（HT = 0.956），居群内平均遗传多样性较低（HS = 0.568）；整个分布区居群间遗传分化程度很低（GST = 0.406，NST = 0.364），并且没有分子系统地理学结构出现（NST < GST）；分子变异分析（AMOVA）也表明，大部分遗传变异（51.75%）存在于居群内部，居群间分化水平较低（FST = 0.483），居群间平均基因流也较低（Nm = 0.535）。 4) 巢式支系法分析表明，就整个支系而言，其历史成因是限制性基因流并伴随着距离隔离。结合单倍型多样性（h）和核苷酸多样性（π）分布格局、歧点分布分析、中性检验及巢式支系法分析推测西川红景天居群可能经历了如下的进化历史：青藏高原隆升和第四纪冰期之前，西川红景天居群的分布范围可能是连续的，基因流频繁，某些古老的单倍型在居群间广泛分布；随着青藏高原的隆升和第四纪冰期气候的反复波动，原来连续的居群片段化，并在青藏高原东南部边缘和高原台面的几个相互隔离的避难所单独保存下来；高原台面占据了西川红景天分布范围的大部分面积，但固定的单倍型较少，并且很多单倍型在高原台面上的居群中没有检测到，表明该地区的居群经历了更严重的瓶颈效应；相互隔离的居群由于缺乏基因流而单独进化，产生大量特有的、遗传分歧很小的单倍型，居群在间冰期或冰期后经历了局部的扩张，扩张过程中的奠基者效应使得某些居群只固定单一的单倍型。
其他摘要	How Quaternary climatic oscillations affected species’ distributions and population genetic structure of alpine plants on the Qinghai-Tibetan Plateau (QTP) is still largely unknown. Most studies conducted on the QTP have argued that populations retreated from the platform to the refugium located at the southeastern margin of the QTP during the Quaternary glaciation, and current populations on the QTP platform expanded from the southeastern refugium during interglacial and/or postglacial periods. Founder effect during population expansion decreased the genetic diversity of populations on the QTP platform. However, other studies thought that some cold-tolerant herbs have survived in refugium which was on the central plateau platform itself during the Quaternary glaciation. Rhodiola alsia (Fröderström) S. H. Fu, belonging to the genus Rhodiola L. of family Crassulaceae, is a perennial herbaceous plant endemic to the Qinghai-Tibetan Plateau. This species is widespread on the QTP from the southeastern margin to the QTP platform at altitudes between 3,400 and 4,800 m above sea level. In this study, phylogeographical analyses have been performed by sequencing two chloroplast DNA (cpDNA) intergenic spacers (trnS-trnG and rpl20-rps12) from 18 R. alsia populations (315 individuals). Genetic variations within and among populations was revealed, and glacial refugia and evolutionary history of R. alsia were also discussed. The main results are as follows: 1) 239 individuals were successfully amplified for the trnS-trnG intergenic spacer. After alignment, the sequence length was 652bp, 85 of which were variable sites with an percentage of 13.04%. The average nucleotide diversity of the trnS-trnG intergenic spacer among the 18 Rhodiola alsia populations was 0.026453. 315 individuals were successfully amplified for the rpl20-rps12 intergenic spacer with an aligned sequence length of 844bp, of which 38 were variable sites with an percentage of 4.50%. The average nucleotide diversity of the rpl20-rps12 intergenic spacer was 0.005233. The percentage of variable sites and average nucleotide diversity of the trnS-trnG intergenic spacer were much higher than that of the rpl20-rps12 intergenic spacer, which indicated a relatively fast evolutionary rate in the trnS-trnG fragment in Rhodiola alsia. Due to fast evolutionary rate, the trnS-trnG intergenic spacer can provide more informative sites with which an relatively accurate phylogenetic relationship among haplotypes can be reconstructed. 2) The amount of haplotypes detected in the trnS-trnG, rpl20-rps12 intergenic spacers and the combined sequences was 23, 31 and 45, respectively. Only a few ancenstral haplotypes (e.g. A2, A6, A7 detected in the trnS-trnG intergenic spacer; H3, H5, H9 in the rpl20-rps12; haplotypes 3 and 8 in the combined sequences) were common and widespread throughout the distributional range of Rhodiola alsia. Most haplotypes were restricted to single sites or to neighbouring populations. Populations (P12-P18) from the southeastern margin of the QTP owned high haplotype diversity and/or nucleotide diversity and fixed more private haplotypes, which suggested that the southeastern margin of the QTP was an important R. alsia refugium during the Quaternary glaciation. Two northernmost (P1 and P6) and westernmost (P8 and P9) populations with high haplotype diversity and/or nucleotide diversity fixed relatively more private haplotypes and were well geographically isolated by the Tanggula Mountains. This distribution pattern of genetic diversity, together with mismatch distribution analysis and neutrality test indicated that two or more R. alsia refugia might exist on the central plateau platform itself during the Quaternary glaciation. 3) Analyses based on the combined sequences of the trnS-trnG and rpl20-rps12 intergenic spacers showed that total gene diversity was especially high (HT = 0.956) and average gene diversity within populations was relatively low (HS = 0.568). The estimates of interpopulation differentiation were low (GST = 0.406，NST = 0.364) with an absence of phylogeographical structure across the distribution range of Rhodiola alsia (NST < GST). Analysis of molecular variance (AMOVA) showed that the genetic variation mainly resided within populations (51.75%) and the FST was 0.483. The average gene flow among populations was 0.535. 4) Nested clade analysis (NCA) indicated that the main historical event acted on the total cladogram was restricted gene flow with isolation by distance. Combined the genetic distribution pattern, mismatch distribution analysis, neutrality test and nested clade alalysis, our results suggested an evolutionary history of R. alsia populations as follows: Before the recent uplift of the Qinghai-Tibetan Plateau and the Quaternary glaciation, populations of R. alsia were continuous, with recurrent gene flow among them. Some ancient haplotypes was distributed across the entire former range of this species. During glaciation, continuous populations of R. alsia were fragmented into several geographically isolated populations which survived in isolated refugia located at the southeastern margin and platform of the QTP. Fewer haplotypes were fixed in the large areas of the plateau platform compared to that in the southeastern margin and some haplotypes were not detected on the plateau platform. This suggests that populations on the plateau platform might have experienced a more serious bottleneck effect and genetic drift than those in the southeastern margin of the plateau during the Quaternary glaciation. Due to very restriced, even entirely absent gene flow, geographically isolated populations evolved independently which formed large amount of private, but not well diverged haplotypes. During interglacial and postglacial periods, population experienced local expansion. Fouder effect occurred during the population expansion should responsible for the low level of haplotype and nucleotide diversity in some populations such as P2, P4, P7 and P10.
页数	104
语种	中文
文献类型	学位论文
条目标识符	http://210.75.249.4/handle/363003/3024
专题	中国科学院西北高原生物研究所
推荐引用方式 GB/T 7714	高庆波. 西川红景天分子系统地理学研究[D]. 西北高原生物研究所. 中国科学院西北高原生物研究所,2009.

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