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1.
横断山地区海仙报春的谱系地理学研究   总被引:2,自引:0,他引:2  
由于横断山地区特殊的地理效应,第四纪冰期气候的反复变化对该地区植物的地理分布和居群遗传结构产生重要影响。为了揭示该地区分布的物种的谱系地理结构,检测了该地区特有的、生于湿地环境的植物海仙报春(Primula poissonii)的叶绿体trnL—F和trnT—L两个序列变异。共对13个居群167个个体的两个叶绿体片段进行测序,共发现11个单倍型。三种单倍型被共享,其他单倍型都只存在于单个居群内。分子变异分析(AMOVA)结果表明分布区内海仙报春的遗传变异主要存在于居群间(99.08%),且居群间的遗传分化很高(GST=0.916,FST=0.99077,NST=0.973),有着极显著的谱系地理学结构(NST〉GST,P〈0.01)和较低的居群间平均基因流(Nm=0.08)。结合嵌套分支分析(NCA),本文的研究结果推测该物种在冰期可能存在多个避难所,并没有表现出大多数温带植物在第四纪冰期所经历过的种群集体扩张和迁移的现象,异域片段化被认为是该物种现有单倍型分布格局形成的主要原因。海仙报春的谱系地理结构是气候的反复波动和横断山特殊的地理环境互相作用的结果。  相似文献   

2.
横断山区作为青藏高原东南部主要的一个冰期避难所,第四纪冰期气候的变化对该地区的植物地理分布和居群遗传结构都产生了重要的影响。为了揭示该地区物种分布的分子系统地理学结构,选取在该地区广泛分布的一种高山灌木-高山绣线菊的叶绿体trnL-trnF序列进行研究。采集了15个居群182个个体进行测序,共发现7个单倍型。总的遗传多样性较高(HT=0.809),但居群内遗传多样性较低(HS=0.236)。分子变异分析(AMOVA)结果表明分布区内高山绣线菊的遗传变异主要存在于居群间(84.48%),且居群间的遗传分化很高(GST=0.708,FST=0.84476,NST=0.863),有着显著的谱系地理学结构(NST>GST,P<0.01)和较低的居群间平均基因流(Nm=0.09)。单倍型的系统进化树和进化分支网络分析得到了相似的拓扑结构,7种单倍型都按照地理分布聚为三支:横断山区西部、横断山区东部以及两者的交接地带。本研究推测该物种在横断山区存在多个冰期避难所,而没有表现出大规模的种群集体扩张和迁移的现象。青藏高原隆升、第四纪气候的反复波动以及横断山区特殊的地理环境使得原来连续的居群片段化,并发生范围扩张,从而塑造了高山绣线菊的现代生物地理分布格局。  相似文献   

3.
由于青藏高原的地貌效应,第四纪冰期气候的反复变化应对现今该地区生物的地理分布及其居群遗传结构产生重大影响。本文对这一地区特有分布物种祁连圆柏Juniperus przewalskii Kom.整个分布区内20居群392个个体的trnT-trnF序列变化进行了研究;共发现3种单倍型(haplotype),构成两种地理区域:高原台面上的居群主要固定Hap A,而Hap A、Hap B和Hap C在高原边缘居群均有分布。所有居群总的遗传多样性HT = 0.511,GST= 0.847。在低海拔的高原边缘,Hap A、Hap B和Hap C高频率固定在不同的居群中,表明可能存在多个不同的避难所,居群反复缩小和扩张的瓶颈效应造成了遗传多样性的丢失。而边缘的一个居群含有两种相似单倍型频率则可能是冰期后迁移融合而成或者该居群在冰期经受的瓶颈作用更弱。高原台面东部间断分布的居群只固定Hap A,表明它们可能经历了冰期后共同的回迁过程和由此产生的奠基者效应。我们的研究结果表明祁连圆柏在冰期可能存在多个避难所,瓶颈效应和奠基者效应造成了这些居群现在的遗传多样性分布式样。  相似文献   

4.
基于叶绿体微卫星研究鄂报春谱系遗传结构   总被引:2,自引:0,他引:2  
鄂报春Primula obconica作为一种广泛栽培的园艺植物,其野生居群的遗传多样性及遗传结构的研究还少见报道。本文通过叶绿体微卫星分析了17个鄂报春野生居群(共278个个体),共发现4个多态性位点(16个等位基因),得到14个单倍型。结果表明鄂报春具有很高的总基因多样性(HT=0.971)和极低的居群内基因多样性(HS=0.028);分子方差分析(AMOVA)显示98%的变异存在于居群间。这些结果说明早期的生境片断化及有限的种子传播能力是造成当前遗传结构的重要原因。Nst值显著大于Gst值,表明关系相近的单倍型会出现在相同的地区内,同时最小生成树(MST)的分析结果证实了这样的结论。我们在最小生成树的两个组中推断出一些古老单倍型,并推测在冰期时湖北和我国的西南地区可能是该物种的避难所。  相似文献   

5.
莛子藨是莛子藨属的一种多年生草本植物,主要分布在青藏高原东北部及邻近高山地区和日本,为东亚特有种。本文基于叶绿体DNA基因间隔区rbcL-accD序列,对莛子藨物种水平的序列特征、分子遗传多样性和谱系地理结构进行研究。分析结果发现该区域莛子藨种群的遗传变异主要来自于居群间(72.28%),优势单倍型(H2)广泛分布,特有单倍型分散在多个居群。居群间遗传分化系数N_(ST)G_(ST),没有检测到显著谱系地理结构,而且居群间基因流较低(N_m=0.096),青藏高原及其邻近地区特殊地形和生态环境造成的地理隔离或者生境异质化可能是现有单倍型分布格局形成的原因。种群动态历史分析显示莛子藨经历过不显著的种群选择或者扩张事件,综合分析推测莛子藨居群应该是在间冰期或者冰期后从不同避难所扩散形成现在的分布格局,具体避难所还需进一步深入研究才能确认。  相似文献   

6.
石甜  莫忠妹  吴敏  赵财 《植物研究》2022,42(4):574-583
对我国14个地区的药食同源植物薤白(Allium macrostemon)的叶绿体基因片段(psbA-trnH、rps16和trnL-F)与核基因片段(ITS)进行测序分析,揭示薤白的遗传变异分布式样、单倍型地理分布格局,并推断其在第四纪冰期的避难所。结果表明:薤白叶绿体基因(cpDNA)遗传多样性低于核基因(nrDNA)遗传多样性(cpDNA:HT=0.868;nrDNA:HT=0.890)。cpDNA和nrDNA的分子变异分析(AMOVA)结果显示:薤白遗传变异主要发生在居群间(cpDNA:92.84%;nrDNA:98.40%),存在遗传分化(cpDNA:Nst=0.918,Gst=0.866,Fst=0.928;nrDNA:Nst=0.984,Gst=0.855,Fst=0.984),且Nst均大于Gst,表明该物种具有明显的谱系地理结构。在薤白居群中,共检测到11个叶绿体单倍型和14个nrDNA基因型;单倍型网络图及地理分布图表明,叶绿体单倍型H3、核DNA基因型H1频率最高,位于网络结构图的中心位置,可能为古老单倍型。此外,冰期避难所假说认为遗传多样性高、拥有古老单倍型和较多特有单倍型的区域可能是该物种的冰期避难所,因此推测薤白在第四纪冰期时可能在大盘山、天水和通化地区存在多个冰期避难所。这些分析可为类似草本植物的进化提供参考,丰富对东亚草本植物分子系统与生物地理学的认识。  相似文献   

7.
利用叶绿体基因(rbcL和trnS-G)及核糖体DNA内转录间隔区(ITS),对祁连山区狭域分布的特有物种黑虎耳草8个居群(115个个体)进行遗传多样性研究,旨在揭示黑虎耳草的居群遗传结构及其历史进化过程。结果表明:(1)所有取样个体共检测到4个cpDNA单倍型和9个ITS单倍型,其中祁连山东南部的居群固定较多的单倍型和特有单倍型,而西北部居群只固定少数几个广泛分布的单倍型,且遗传多样性普遍较低。(2)基于cpDNA数据和ITS数据的分子变异分析(AMOVA)显示,遗传变异主要来源于居群内。(3)基于cpDNA数据的中性检验表明,Tajima’s D(-1.012 30,P 0.05)和FuLi’s D*(-2.066 77,P 0.05)均为负值,均不显著;歧点分布分析结果显示,黑虎耳草居群经历过近期的扩张事件。根据物种现有遗传分布格局推测,黑虎耳草在第四纪冰期时退缩到祁连山东南部的边缘避难所,间冰期或冰期后回迁到祁连山西北部地区,在回迁过程中由于奠基者效应导致祁连山西北部的居群仅固定少数广泛分布的单倍型,并呈现出较低的遗传多样性;由于居群较小且相互隔离,该物种经历了严重的瓶颈效应和遗传漂变,导致该物种总遗传多样性(H_T)和居群平均遗传多样性(H_S)远低于虎耳草属其他青藏高原-喜马拉雅广域分布的物种。  相似文献   

8.
利用叶绿体DNA非基因编码区rpl20-rps12和trn L-trn F作为分子标记,对喜马拉雅—横断山区优越虎耳草13个居群151个个体进行谱系地理学研究,旨在揭示优越虎耳草现有的遗传结构及其演化历程。共检测到19个单倍型,其中63%的单倍型为居群特有单倍型。研究还发现,优越虎耳草居群总的遗传多样性较高(H_t=0. 868),居群内平均遗传多样性较低(H_s=0. 466)。分子变异分析(AMOVA)表明,优越虎耳草居群57. 37%的遗传变异来自居群内,居群间遗传变异为42. 63%。居群遗传分化系数N_(st)大于G_(st)(N_(st)=0. 463,G_(st)=0. 438,P0. 05),但不显著,表明优越虎耳草在其整个分布范围内没有明显的谱系地理结构。中性检验结果表明,Tajima’s D为负值(-1. 348 32,P 0. 05)而Fu’s F_s*为正值(18. 915 72,P 0. 05),但均不显著,结合歧点分布分析发现该物种在整个分布范围内未经历过居群扩张。此外,在本研究中优越虎耳草遗传多样性和核苷酸多样性较高的居群及大量特有单倍型在整个分布范围内随机分布,符合"微型避难所"假说。优越虎耳草居群在冰期可能随气候波动而发生分布范围的不断变化,最终在相互隔离的"高山岛屿"中发生异域分化,导致大量特有单倍型产生。因此,推测优越虎耳草与其生境中的乔木和灌木可能具有相似的谱系地理历史,它们可为优越虎耳草提供微型避难所而使之在冰期时保留下来。  相似文献   

9.
南方红豆杉谱系地理学研究   总被引:2,自引:0,他引:2  
通过对南方红豆杉18个居群499个个体叶绿体基因组的trnL-F片段进行RFLP分析,共检测到6个叶绿体DNA单倍型,其中除台湾居群外的17个居群都包含有单倍型H1和H2;黄山及临安居群除单倍型H1、H2外,还分别各有1个特有单倍型。谱系关系分析显示,单倍型H1、H2为较古老的祖先单倍型。AMOVA分析显示,变异主要存在于居群内,居群间的遗传分化程度较低(26.39%)。嵌套分支分析(NCA)显示,单倍型分布与地理分布存在轻度的地理相关性,南方红豆杉现在的遗传结构可能源于居群的片段化效应,台湾居群可能是由于曾经的居群片段化而隔离或长距离扩散所致;在第四纪冰期,中国东、南部地区可能存在2个以上南方红豆杉的避难所。  相似文献   

10.
高山植物条纹狭蕊龙胆的分子亲缘地理学研究   总被引:1,自引:0,他引:1  
草本植物由于较短的生活周期以及对环境变化的敏感性,可能会更好地揭示第四纪冰期以来植物居群变化的历史过程.分子亲缘地理学研究是揭示动植物居群历史的有力工具,但到目前为止对青藏高原草本植物的分子亲缘地理学研究几乎是空白.因此,本文选择在青藏高原及邻近地区生长的一年生高山草本植物条纹狭蕊龙胆为研究对象,进行了13个居群155个个体的叶绿体基因组(cpDNA)非编码片段trnH(GuG)-psbA基因间区序列变异检测,共发现7种单倍型,其中单倍型H印A是分布最广的,而单倍型Hap E、Hap F和Hap G是拥有的居群所特有的.青藏高原东北部、东部及邻近地区的每个居群拥有的单倍型非常单一,而高原东南部横断山区的单倍型分布很集中,遗传多样性也相对较高.分子变异分析(AMOVA)结果表明整个分布区条纹狭蕊龙胆的遗传变异主要存在于居群间(73.05%),且居群问的遗传分化很高(GsT=0.805,FsT=0.731,NsT=0.859),有着显著的亲缘地理学结构(NsT>Gsr,P<0.05)和较低的居群间的平均基因流(Nm=0.184).结合巢式支系法分析(NCA),根据本文的研究结果推测青藏高原东南部横断山区是该植物第四纪冰期时可能的避难所,而且在间冰期或冰期后.伴随着异域片段化和过去片段化从避难所发生范围扩张而形成当前单倍型及居群的分布格局.  相似文献   

11.
To date, little is still known about how alpine species occurring in the Qinghai-Tibetan Plateau (QTP) responded to past climatic oscillations. Here, by using variations of the chloroplast trnJ-L, we examined the genetic distribution pattern of 101 individuals of Potentilla glabra, comprising both the interior QTP and the plateau edge. Phylogenetic and network analyses of 31 recovered haplotypes identified three tentative clades (A, B and C). Analysis of molecular variance (amova) revealed that most of the genetic variability was found within populations (0.693), while differentiations between populations were obviously distinct (Fst = 0.307). Two independent range expansions within clades A and B occurring at approximately 316 and 201 thousand years ago (kya) were recovered from the hierarchical mismatch analysis, and these two expansions were also confirmed by Fu's Fs values and 'g' tests. However, distant distributions of clade C and private haplotypes from clades A and B suggest that they had survived the Last Glacial Maximum (LGM) and previous glaciers in situ since their origins. Our findings based on available limited samples support that multiple refugia of a few cold-enduring species had been maintained in the QTP platform during LGM and/or previous glacial stages.  相似文献   

12.
Aim Palaeontologial data suggest that all temperate forest species in northern China migrated southwards during the Last Glacial Maximum (LGM) and recolonized post‐glacially within the Holocene. We tested this assumption using phylogeographical studies of a temperate deciduous shrub species (Ostryopsis davidiana Decne., Betulaceae), which has a wide distribution in northern China. Location Northern China. Methods We sequenced two chloroplast DNA (cpDNA) fragments (trnL–trnF and psbA–trnH, together about 1300 bp in length) of 294 plants from 21 populations across the total distribution range of this species. We used maximum parsimony and haplotype network methods to construct phylogenetic relationships among haplotypes. Results The analysis of cpDNA variation identified eight haplotypes. A single haplotype was fixed in all populations except for one population that was polymorphic, having two haplotypes. The population subdivisions were extremely high (GST = 0.972 and NST = 0.974), suggesting very low gene flow between populations. Haplotypes clustered into two tentative clades, both of which occur in the southern region of the species’ range but only one of which occurs in the northern region. Across the sampled populations, the haplotype distributions were differentiated geographically. Main conclusions Our analyses suggest that multiple refugia were maintained across the range of O. davidiana in both northern (north of the Qing Mountains) and southern (south of the Qing Mountains) regions during the LGM rather than that the species survived only in the south and subsequently colonized northwards. The extremely low within‐population diversity of this species suggests strong bottleneck or founder effects within each fragmented region during the Quaternary climatic oscillations. These findings provide important clues for understanding range shifts and changes in within‐ and/or between‐population genetic diversity of temperate forests in response to past climatic oscillations in northern China.  相似文献   

13.
Nothofagus pumilio is the dominant and almost ubiquitous tree species in mountainous environments of temperate South America. We used two types of molecular markers (cpDNA and isozymes) to evaluate the effects of the Paleogene paleogeography of Patagonia and more recent climatic oscillations of the Neogene on such cold‐tolerant species’ genetic makeup. Phylogeographic analysis on sequences of three cpDNA non‐coding regions at 85 populations yielded two latitudinally disjunct monophyletic clades north and south of c. 42°S containing 11 and three haplotypes, respectively. This indicates a long‐lasting vicariant event due to the presence of an extended open paleobasin at mid latitudes of Patagonia. Also distribution patterns of cpDNA haplotypes suggest regional spread following stepping‐stone models using pre‐Cenozoic mountains as corridors. Comparable genetic diversity measured along 41 sampled populations using seven polymorphic isozyme loci provides evidence of local persistence and spread from multiple ice‐free locations. In addition, significantly higher heterozygosity and allelic richness at high latitudes, i.e. in areas of larger glacial extent, suggest survival in large and isolated refugia. While, higher cpDNA diversity in lower latitudes reflects the complex orogeny that historically isolated northern populations, lower isozyme diversity and reduced FST values provide evidence of local glacial survival in numerous small locales. Therefore, current genetic structure of N. pumilio is the result of regional processes which took place during the Tertiary that were enhanced by contemporary local effects of drift and isolation in response to Quaternary climatic cycles.  相似文献   

14.
It has been suggested that the eastern Asian temperate flora have responded to Quaternary climatic changes in a different way compared with temperate plants in Europe and Northern America. However, knowledge about their phylogeographic structure and evolutionary history is still limited. In this study we investigated mitochondrial DNA variation in 17 populations of Pinus kwangtungensis, a five-needled pine inhabiting in isolated mountains of southern China and northern Vietnam. A total of ten mitochondrial haplotypes (mitotypes) were characterized by the polymorphisms of two fragments (cox-1-2 and nad7 intron1), and total genetic diversity was high (h T = 0.847). The construction of phylogenetic relationships of the ten mitotypes detected three major, well-distinct clades, largely corresponding to four population groups identified by SAMOVA analysis. SAMOVA also indicated that most genetic variance should be attributed to among-group differentiation (F CT = 0.868), consistent with the substantial genetic structure found within P. kwangtungensis (G ST = 0.751). The genetic distances of P. kwangtungensis weakly but significantly correlated with geographical distances (R = 0.228, P = 0.03), revealing a pattern of isolation-by-distance. Demographic analysis did not detect any bottleneck events in the recent history of P. kwangtungensis. These results clearly suggested that there were three major refugia for this montane temperate conifer during warm stages (along with other minor refugia), and that the species would have tracked Quaternary climatic changes by expanding to nearby lowlands in the glacial periods, and by retreating to mountaintops (the refugia) during interglacial warmer stages, experiencing fragmentation and isolation among refugia.  相似文献   

15.
Mediterranean mountain ranges harbour highly endemic biota in islandlike habitats. Their topographic diversity offered the opportunity for mountain species to persist in refugial areas during episodes of major climatic change. We investigate the role of Quaternary climatic oscillations in shaping the demographic history and distribution ranges in the spider Harpactocrates ravastellus, endemic to the Pyrenees. Gene trees and multispecies coalescent analyses on mitochondrial and nuclear DNA sequences unveiled two distinct lineages with a hybrid zone around the northwestern area of the Catalan Pyrenees. The lineages were further supported by morphological differences. Climatic niche‐based species distribution models (SDMs) identified two lowland refugia at the western and eastern extremes of the mountain range, which would suggest secondary contact following postglacial expansion of populations from both refugia. Neutrality test and approximate Bayesian computation (ABC) analyses indicated that several local populations underwent severe bottlenecks followed by population expansions, which in combination with the deep population differentiation provided evidence for population survival during glacial periods in microrefugia across the mountain range, in addition to the main Atlantic and Mediterranean (western and eastern) refugia. This study sheds light on the complexities of Quaternary climatic oscillations in building up genetic diversity and local endemicity in the southern Europe mountain ranges.  相似文献   

16.
The geographical distribution of chloroplast DNA (cpDNA) haplotypes and nuclear ribosomal internal transcribed spacer (nrITS) genotypes of Japanese Corylopsis (Hamamelidaceae), which consists of four species, was investigated. Two hundred and five individuals belonging to four species from 30 populations, covering the entire geographical range, were studied. Based on approximately 1108 bp of the three non-coding regions of cpDNA, nine haplotypes were detected, and each was distinguished from adjacent haplotypes by one substitution. Based on approximately 507-bp nrITS sequences, 47 genotypes were detected, for which three clades were identified in the phylogenetic analysis. There was inconsistency between the cpDNA haplotypes, nrITS genotypes, and classification of Corylopsis taxa, possibly because of incomplete lineage sorting or introgressive hybridization. The distribution of the haplotypes was highly structured geographically, and N ST (0.893) was significantly greater than G ST (0.819), implying that the current distribution of Corylopsis species was structured phylogeographically during Quaternary climatic oscillations. The haplotype composition and results of analysis of molecular variance showed that the populations in Hokuriku were highly divergent, suggesting that they are long-term persistent populations arising from refugia during the Quaternary climatic oscillations. Refugial populations in Chugoku and Shikoku may have lost genetic diversity because of a bottleneck resulting from a small population size, followed by post-glacial range expansion. Pre-existing refugia may have been so small that the subsequent range expansion replaced the pre-existing genetic structure.  © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society , 2008, 157 , 501–518.  相似文献   

17.
基于叶绿体DNA trnL-F序列研究肋果沙棘的谱系地理学   总被引:1,自引:0,他引:1  
由于青藏高原的地理效应,第四纪冰期气候的反复变化应对现今该地区生物的地理分布及其居群遗传结构产生重大影响。肋果沙棘Hippophae neurocarpa是青藏高原地区的一个特有种,根据叶上的附属物(星状鳞毛或者鳞片状鳞毛)分为两个亚种:肋果沙棘亚种subsp.neurocarpa和密毛肋果沙棘亚种subsp.stellatopilosa。依据母系遗传的叶绿体DNA片段对该物种谱系地理学进行研究不仅能阐明该物种冰期避难所,而且对于理解两个亚种的母系分化也具有重要意义。共对两个亚种14居群的70个个体的trnL-F序列进行了测序,共发现8种单倍型,其中5种单倍型出现在肋果沙棘亚种中,4种出现在密毛肋果沙棘亚种中,两个亚种共享一种单倍型。种内谱系分化与两个亚种形态上的分化不一致。嵌套进化分支把8种单倍型分为三支:一支为肋果沙棘亚种,其他两支中两个亚种单倍型嵌套组成,且肋果沙棘亚种处于进化末端。我们的研究结果还表明肋果沙棘在冰期可能在高海拔地区存在多个避难所,并且存在来自避难所的邻域扩张。  相似文献   

18.
How Quaternary climatic oscillations affected range distributions and intraspecific divergence of alpine plants on the Qinghai‐Tibetan Plateau (QTP) remains largely unknown. Here, we report a survey of chloroplast DNA (cpDNA) and nuclear ribosomal internal transcribed spacer (ITS) DNA variation aimed at exploring the phylogeographical history of the QTP alpine endemic Aconitum gymnandrum. We sequenced three cpDNA fragments (rpl20–rps12 intergenic spacer, the trnV intron and psbA‐trnH spacer) and also the nuclear (ITS) region in 245 individuals from 23 populations sampled throughout the species’ range. Two distinct lineages, with eastern and western geographical distributions respectively, were identified from a phylogenetic analysis of ITS sequence variation. Based on a fast substitution rate, these were estimated to have diverged from each other in the early Pleistocene approximately 1.45 Ma. The analysis of cpDNA variation identified nine chlorotypes that clustered into two major clades that were broadly congruent in geographical distribution with the two ITS lineages. The east–west split of cpDNA divergence was supported by an amova which partitioned approximately half of the total variance between these two groups of populations. Analysis of the spatial distribution of chlorotypes showed that each clade was subdivided into two groups of populations such that a total of four population groups existed in the species. It is suggested that these different groups derive from four independent glacial refugia that existed during the Last Glacial Maximum (LGM), and that three of these refugia were located at high altitude on the QTP platform itself at that time. Coalescent simulation of chlorotype genealogies supported both an early Pleistocene origin of the two main cpDNA clades and also the ‘four‐refugia’ hypothesis during the LGM. Two previous phylogeographical studies of QTP alpine plants indicated that such plants retreated to refugia at the eastern/south‐eastern plateau edge during the LGM and/or previous glacial maxima. However, the results for A. gymnandrum suggest that at least some of these cold‐tolerant species may have also survived centrally on the QTP platform throughout the Quaternary.  相似文献   

19.
The evolution and current distribution of the Sino-Tibetan flora have been greatly affected by historical geological events, such as the uplift of the Qinghai-Tibetan Plateau (QTP), and Quaternary climatic oscillations. Rhodiola kirilowii, a perennial herb with its distribution ranging from the southeastern QTP and the Hengduan Mountains (HM) to adjacent northern China and central Asia, provides an excellent model to examine and disentangle the effect of both geological orogeny and climatic oscillation on the evolutionary history of species with such distribution patterns. We here conducted a phylogeographic study using sequences of two chloroplast fragments (trnL-F and trnS-G) and internal transcribed spacers in 29 populations of R. kirilowii. A total of 25 plastid haplotypes and 12 ITS ribotypes were found. Molecular clock estimation revealed deep divergence between the central Asian populations and other populations from the HM and northern China; this split occurred ca. 2.84 million year ago. The majority of populations from the mountains of northern China were dominated by a single haplotype or ribotype, while populations of the HM harbored both high genetic diversity and high haplotype diversity. This distribution pattern indicates that HM was either a diversification center or a refugium for R. kirilowii during the Quaternary climatic oscillations. The present distribution of this species on mountains in northern China may have resulted from a rapid glacial population expansion from the HM. This expansion was confirmed by the mismatch distribution analysis and negative Tajima''s D and Fu''s F S values, and was dated to ca. 168 thousand years ago. High genetic diversity and population differentiation in both plastid and ITS sequences were revealed; these imply restricted gene flow between populations. A distinct isolation-by-distance pattern was suggested by the Mantel test. Our results show that in old lineages, populations may harbour divergent genetic forms that are sufficient to maintain or even increase overall genetic diversity despite fragmentation and low within-population variation.  相似文献   

20.
Climate changes during glacial periods have had significant effects on the current distribution of plant species. Palaeontologial data suggest that modern cycads originated in southwest China. Cycas debaoensis (Cycadaceae) is an endangered species restricted to a small area of southwest China. This species has been classified into two types: sand and karst, according to the soil matrix they grow on. To determine the locations of its glacial refugia and its genetic structure, we examined chloroplast sequence variation of the atpB-rbcL and psbA-trnH intergenic spacers. Four chloroplast DNA haplotypes were obtained from 120 individuals collected from 11 populations covering the entire extant distribution range of the species. Significant population subdivision was detected (G ST = 0.684 and F ST = 0.74160), suggesting low levels of gene flow between regions and populations. There was marked haplotype differentiation between populations in the sand and karst regions, with only one haplotype being present in both. The molecular phylogenetic data, together with the geographic distribution of the haplotypes, suggest that C. debaoensis experienced range contraction during glacial periods, and that the current populations are still confined to the areas of the original refugia. These results implied that isolated refugia might have maintained in both sand and karst regions during the last glacial maximum and even earlier glaciations. The low within-population diversity of C. debaoensis suggested that there were strong bottleneck events or founder effects within each separate region during the Quaternary climatic oscillations. These findings are important for the conservation of this endangered species.  相似文献   

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