中国西南地区膜叶铁角蕨属的多倍体起源和网状进化研究

Hymenasplenium was recognized as a genus in the present generic delimitation of the family Aspleniaceae. It is a well-defined group with unusual dorsiventral vascular system in long creeping rhizomes and chromosome base numbers differing from typical of Asplenium of x=36. Members of Hymenasplenium are widely distributed in the tropic zones of the world. Southwestern China is the place with the highest diversity of Hymenasplenium species. Moreover, cytologically and reproductively abundant basal forms of Hymenasplenium exist in Southwestern China supporting the assumption that this region is a diversity center of the genus. The Asian members of Hymenasplenium have been extensively investigated particularly in cytology. Polyploidy is common in Hymenasplenium and reticulate evolution is suggested, making this fern group a good model for study of plant systematics and evolutionary biology. Besides, Hymenasplenium can be one of the best materials for studying the evolutionary and ecological significance of sexual reproduction because several pairs of sexual and apogamous races are known. The species classification and evolution of Hymenasplenium, however, is still poorly known. To know the polyploidy origin and reticulation of Hymenasplenium have a major importance when studying the complex evolution of this genus which is well known of its great variation in cytology, morphology and ecology. In our previous studies, phylogeny and reticulation of the Asplenium normale complex were successfully revealed by using four regions of the maternally inherited chloroplast genome and one biparentally inherited marker, the single-copy nuclear gene pgiC, and determining ploidy levels of samples by measuring spore size and determining DNA C-values by flow-cytometric analysis of selected specimens. Therefore, we hypothesized that ploidy levels and DNA sequencing studies, particularly comparisons of phylogenetic analyses of nuclear and chloroplast sequences among polyploids and their proposed progenitors, can reveal reticulate evolutionary patterns and resolve taxonomic challenges in Hymenasplenium. In this study, we plan to focus on the polyploidy origin and reticulation of Hymenasplenium in Southwestern China. We will infer ploidy level from spore measurements, flow-cytometric analysis and chromosome observation. We will assess reproductive mode by counting spore numbers per sporangium. Then we will use sequences from plastid regions and two single copy genes to infer polyploidy origin and reticulation from incongruence between gene trees and from cloning and sequencing duplicated loci in polyploidies. The results of this research will provide insight into the evolutionary strategies and causes of variations in Hymenasplenium in Southwestern China. Finally, our study will help to understand speciation processes and evolution of Hymenasplenium and contribute to the debate about the taxonomy of this genus.

膜叶铁角蕨属约30余种，具有丰富的细胞倍性和多样的繁殖方式，是进化生物学研究中不可多得的模式类群。中国西南地区是膜叶铁角蕨属的物种多样化中心及可能的起源和分化中心。本研究拟重点以中国西南地区分布的膜叶铁角蕨属植物为研究对象，应用多学科研究手段，综合形态学、细胞学和遗传学数据，并结合地理分布格局和生境特征，全面深入地研究中国西南地区膜叶铁角蕨属多倍体类群的起源及可能的网状进化模式。本项目的研究结果最终将可能揭示该类群植物在染色体数目、繁殖方式、生境适应及形态特征等方面进化适应上采取的不同分子进化策略，并解释其丰富的多样性形成的原因。本研究还将为探讨膜叶铁角蕨属的系统演化和物种分类提供新的线索和较完全的信息，并为铁角蕨类植物物种形成和进化机制的研究提供重要证据。

膜叶铁角蕨属约50余种，具有丰富的细胞倍性和多样的繁殖方式，是研究进化生物学不可多得的模式类群。而我国的西南地区是该属植物的物种多样化及物种起源分化中心。本项目主要以分布中国西南地区的膜叶铁角蕨属及相关类群为研究材料，并获得了部分我国台湾、日本和非洲等地区的关键研究材料，应用多学科研究手段，综合形态学、细胞学和遗传学数据，并结合地理分布格局和生境特征，对中国西南地区分布的膜叶铁角蕨属的物种多样性及其多倍体类群可能的起源及网状进化模式进行了研究。研究结果如下：.1，.形态学研究结果表明，叶片、羽片及根状茎的形态特征是区别膜叶铁角蕨属中大部分物种的关键特征，而根状茎上的鳞片及孢子形态在大部分物种中并没有太大的区别。.2，.细胞学研究结果表明，在大部分的复合群类群中可能存在着不同的细胞倍性，如荫湿膜叶铁角蕨类群、切边膜叶铁角蕨类群及与半边铁角蕨相关的几个类群等等。孢子囊内孢子计数的方式初步验证了无配膜叶铁角蕨、齿果膜叶铁角蕨等类群中存在的无融合生殖的类群，但是要验证其生殖方式和细胞倍性还需要进一步详细的研究。.3，.分子生物学研究结果表明，中国以前被鉴定为半边铁角蕨的类群内至少存在四个分类群，其中三个为英文版中国植物志承认的物种，即单边膜叶铁角蕨、东亚膜叶铁角蕨和无配膜叶铁角蕨，另一个为我们新发表的H. laterepens。这些分类群与非洲产的半边膜叶铁角蕨是不同的类群。核基因分析结果还表明在中国西南地区产的膜叶铁角蕨属的荫湿膜叶铁角蕨蕨类群及与半边膜叶铁角蕨相关的几个类群中可能存在比较复杂的网状进化关系。.通过本项目对中国西南地区产的膜叶铁角蕨属类群的研究发现，在该类群中，物种起源和物种分化与多倍化及杂交现象有密切的关系。彻底阐明该类群的物种分类和物种多样性形成需要对该类群的细胞倍性及生殖模式，及其在生态适应上的分子策略做进一步深入的研究。