KIB OpenIR  > 昆明植物所硕博研究生毕业学位论文
Thesis Advisor龚洵 ; 彭华 
Degree Grantor中国科学院研究生院
Degree Discipline植物学
Abstract叉叶苏铁复合体是一个以羽叶二叉分歧为主要特征的自然类群,由形态相近的叉叶苏铁、越南叉叶苏铁、长柄叉叶苏铁、德保苏铁和多歧苏铁5个类群组成,主要分布于我国西南部以及越南北部、中南部及老挝东南部。本论文基于两个母系遗传的叶绿体基因片段和一个双亲遗传的核糖体基因片段对其谱系地理和遗传结构进行研究,并依据这些结果对叉叶苏铁复合群内各种间的演化关系和种群动态历史进行探讨,主要研究结果如下:1. 叉叶苏铁复合群的叶绿体基因与核基因单倍型的分化均表现出较强的地域性:27个居群的叶绿体单倍型分成三个组与地理分布明显相关,即云南组、广西组和越南组;而核基因单倍型分成两个组也与叉叶苏铁复合群的两大分布地域:中国和越南对应。2. 叉叶苏铁复合群的内部分类关系:支持德保苏铁、多歧苏铁的划分;之前划分的叉叶苏铁与越南叉叶苏铁应归并为同一个种叉叶苏铁(C. micholitzii);长柄叉叶苏铁与云南分布的叉叶苏铁亲缘关系最近。3. 渐新世开始中南半岛与中国大陆南部之间的分离运动,使得原本同域分布的叉叶苏铁分成今天地理上相距甚远的两大类群。两地区居群的叶绿体基因交错分布,主要原因是分化时间不够造成的谱系分选不完全;而核基因谱系结果与地理分布一致,这与同地域较强的花粉流以及ITS较快的进化速率有关。 4. 德保苏铁依靠西南地区河谷有利的生境及气候条件渡过冰期,从而成为第四纪冰期的残遗群落。砂页岩与石灰岩地区的居群间存在的遗传分化主要是对不同生境的一种适应分化。5. 支持以前古植物地理研究观点:“苏铁植物在冰期后没有发生大规模的迁移和长距离的扩散,主要还是在原地生存以至延续至今”。6. 保育建议:由于叉叶苏铁复合群居群间呈现高度的遗传分化,大部分居群含有特有单倍型。因此建议在野生居群比较密集的地方建立保护区,尽量保护更多居群。
Funding ProjectCycas micholitzii complex is composed of 5 species: C. micholitzii Dyer, C. bifida (Dyer) K. D. Hill,C. longipetiolula D. Y. Wang, C. debaoensis Y. C. Zhong et C J. Chen, C. multipinnata C J. Chen et S. Y. Yang,and distributed from southwest China to central Vietnam and eastern Laos. Based on sequence data from two maternally inherited cpDNA and one biparentally nuclear DNA fragments, our study revealed the population genetic structure of C. micholitzii complex and explored the potential causes. The evolutionary and demographic histories were investigated. The genetic relationship among species in the complex was also clarified.The results were summarized as follows: 1. Phylogeographic analysis based on chloroplast sequences,We examined chloroplast sequence variation of the atpB-rbcLand psbA-trnHintergenic spacers in 27 populations of C. micholitzii complex, recovering 26 haplotypes. The average within-population diversity (HS = 0.140) was low while total diversity (HT = 0.911) was high. Population differentiation was also high(GST = 0.846, NST = 0.919), indicating significant phylogeographical structure (NST > GST,p < 0.001) and low levels of seed-based gene flow. C. debaoensis (Cycadaceae) is an endangered species restricted to the border of Guangxi and Yunnan province in southwest China. This species has been classified into two types: sand and karst, according to the soil matrix they grow on. We examined chloroplast sequence variation of the cpDNA sequences from 11 populations of this species. Significant population genetic differentiation was detected (GST= 0.684 and FST = 0.74160). There was marked genetic differentiation between populations in the sand and karst regions and no expansion was detected. Climate changes during glacial periods have had significant effects on the current distribution of cycads. 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 original refugia in southwest China which have favorable habitats in glacial period. These results imply that small refugia were maintained in both sand and karst regions during the LGM (last glacial maximum). This species had no postglacial recolonization and only stayed in these refugia up to now. The low within-population diversity of C. debaoensis suggests that there were strong bottleneck events or founder effects within each separate region during the Quaternary climatic oscillations. Relatively high genetic and haplotype diversities were detected in the newly discovered populations, which located at intermediate locality of sand regions and had morphological variation; this is probably the consequence of the admixture of different haplotypes colonizing the area from separate sources. C. micholitzii occurs in the Annan Highlands in central Vietnam near the Laos border. C. bifida occurs in North Vietnam; its distribution extends across the border into adjacent localities in Guangxi and Yunnan in China. For the comparability between them,theywere considered as the same species C. micholitzii by many academicians. The cpDNA sequences from 11 populations showed that these very controversial species, C. micholitzii and C. bifida, is paraphyletic and should belong to the same species C. micholitzii. AMOVA analysis showed that the component of among-population within region/species (76.46%) was unexpectedly larger than the among-species/region component (14.97%), which also indicates that there is no justification for recognizing two species as C. micholitzii and C. bifida. This hypothesis was also supported by the geological data, especially the neotectonic history of the indo-china block, which started to move south since Oligocene and cause the geographic isolation of these two groups. Therefore, the most likely explanation to the phenotypic similarities between these two groups may be the retention of ancestral polymorphisms in the paraphyletic group due to incomplete lineage sorting. Furthermore, the similarities may also be ascribed to pollen-mediated gene flow among geographically proximate populations and/or phenotypic convergence under similar selection schemes in the same region. C.micholitzi had the higest genetic diversity (HT = 0.980,) and genetic differentiation (GST = 0.830, NST = 0.915) among the C. micholitzii complex. The high genetic diversity might be attributed to its long evolutionary history, highly diverse habitats. The ineffective mode of seed dispersal and dramatic neotectonic movement in the distribution range of this species could result in the high genetic differentiation. 2. Phylogeographic analysis based on nuclear ribosomal sequences, We sequenced the nrDNA ITS in all 27 populations sampled, 7 haplotypes were identified, among which C. micholitzii had 6, while C. multipinnata, C. longipetiolula and C. debaoensis shared the remaining one. Compared to chloroplast genes, nuclear genes had higher correlation between genetic and geographical distance, but lower interspecies differentiation (54.42% vs 25.24%). Phylogeographical structure of C. micholitzii and C.bifida based on ITS Variation was consistent with the morphology differentiation. This similar in nuclear gene should be ascribed to pollen-mediated gene flow among geographically proximate populations.Long-distance gene flow over the two groups was clearly interrupted, which brought on the nrDNA genetic differenciation between the geographically isolated groups, to a certain extent affected the morphological variation. 3. Interspecies relationships among Cycas micholitzii complex, We analysed chloroplast sequence variation of the atpB-rbcL and psbA-trnH intergenic spacers in 27 populations sampled of C. micholitzii complex, AMOVA analysis showed that the component of among-species/region component (59.21%). However, phylogenic analysis showed that the haplotypes of C. micholitzii complex couldn`t grouped into four clusters closely corresponding to the narrowly defined C. micholitzi, C. multipinnata, C. debaoensis and C. longipetiolula. We concluded that the conflict may result from several factors: firstly incomplete lineage sorting of C. micholitzii; secondly hybridization/introgression of sympatrically cycads, which would be supported by evidence base on nrDNA ITS sequences; thirdly intramolecular recombination in cpDNA of cycads; eventually the neotectonic movement in the distribution range of this species.
Document Type学位论文
Recommended Citation
GB/T 7714
湛青青 . 叉叶苏铁复合群的谱系地理学研究 [D]. 中国科学院研究生院,2010.
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