【作者】 俞英；

【导师】 朱瑞良； Harald Schneider；

【作者基本信息】 华东师范大学 ， 植物学， 2013， 博士

【摘要】 虽然分子数据提供的丰富证据极大地促进了我们对于苔藓植物分类学和系统学的了解,然而在当前的苔藓植物分类学中还是主要依靠形态性状来进行新物种的界定。越来越多的分子系统发育研究已表明在苔类植物支系中单独的形态证据已经不能够很好地用来揭示支系间的系统关系和界定物种。关于分子与形态数据之间的矛盾,系统和分类学家也提出了诸多的假设,例如形态性状的平行进化或者趋同进化和隐种的存在。特别是生长在极端环境中的植物支系,由于受到极端环境的稳定性选择压力,频繁地出现形态性状的异源同形或者隐种现象。疣鳞苔属植物是衍生苔类植物中的大属之一,偏好叶附生环境。由于疣鳞苔属植物体个体小,这意味着这类支系有限的形态空间及极端的生长环境,我们推测当前的疣鳞苔属植物的分类学采用形态物种的定义已不能真正揭示该属内的真正物种。在本项研究中,我们主要通过三个途径来支持我们对于疣鳞苔属植物性状进化的假设。首先利用DNA序列建立可靠的疣鳞苔属植物的系统发育树,在此基础上寻找早期认为具有分类学价值的形态性状的异源同型证据；其次推断疣鳞苔属植物的遗传分化和形态多样性的相关性；最后我们采用DNA分类学方法去比较建立在形态证据和建立在分子证据上的分类学对于物种界定的差异。我们得到以下结果：(1)我们利用132个样本和三个基因片段(rbcL, trnL-F, nrITS)首次建立疣鳞苔属及邻近属的系统发育关系。分子证据证实了内组群中共有三大支系Colura, Myriocoleopsis和Cololejeunea。Myricoleopsis与疣鳞苔属的Cololejeunea minutissima形成了一个支持率高的支系。Aphanolejeunea和Chondriolejeunea被归入到Cololejeunea支系中。Cololejeunea angustiflora和Cololejeunea magnilobula形成的支系与由剩余疣鳞苔属植物组成的支系形成姐妹支系群。当前形态定义的亚属分类单元在系统树上出现双系或者多系起源。其中在31个含2个或者多个样本的形态物种中,有7个证实是非自然分类单位。研究结果证实了经常用于疣鳞苔属植物分类学的形态性状具有较高水平的异源同型或者趋同进化水平,而这些现象的存在正可以解释在该属植物形态分类学中存在的大量的争论。本次研究并没有在主要支系或者相关的跨州分布物种中找到早期地理隔离的证据,反而找到了近期远距离传播的证据。(2)我们在进行系统发育和形态距离矩阵的相关性分析中,形态距离矩阵主要采用了70个疣鳞苔属植物MTSs (Morphological-typological specie)和13个配子体及生活史相关的形态特征。而系统发育距离矩阵则建立在三个基因片段(rbcL,trnL-F, nrITS)的和两种不同距离方法上：Patristic和Hamming。两类矩阵的Mantel测试结果显示疣鳞苔属的9个配子体的性状分化与遗传分化具有相关性,而生活史相关特征则可能由于性状频繁的趋同进化或者随机漂变导致与遗传多样性的相关性的丧失。推测疣鳞苔属植物的性状分化程度随性状和支系的不同而不同。因此在不同支系选择形态性状进行分类学研究时需要更加谨慎。(3)我们采用了DNA分类学中的统计学物种界定标准,测量疣鳞苔属植物中单系群Cololejeunea lanciloba组群中的遗传差异,探索该组群内的隐种现象。我们采用了两个基因片段(trnL-F, nrITS)和62个样本。结果显示在C. lanciloba组群内的4个MTSs中检测到了13个具有显著遗传差异的分子分类单元,证实了该组群中隐种的存在。个别MTSs中样本不仅出现在多个支系中,而且个别支系中出现了不同的表现型,说明了疣鳞苔属不同支系性状分化具有一定的限制性或者可塑性。此项研究中我们比较了采用传统的支系起源判断物种的方法和P(AB)和P(BD)的物种界定的方法,证实了新引入的统计学物种界定标准在遗传差异的检测中更加敏感。这也是在苔藓植物支系中首次运用此类物种界定标准。该项研究同时也支持了Boykin "tip-to-root"的方法在植物物种界定中的可行性。总之,我们建立了可靠的疣鳞苔属植物及其相邻支系的系统发育关系,构建了该属植物的分类学框架,解决了几个长期困扰的属间和亚属分类学问题。通过构建疣鳞苔属系统发育树进而研究其性状进化,揭示了该属植物的性状进化存在频繁的异源同形现象。该现象可能是该类群受到叶附生环境的稳定选择压力及本身有限的发育选择而导致的。而这种现象的存在也可以用来解释只在部分的疣鳞苔属植物支系中检测到了形态多样性和遗传分化之间的相关性。隐种是疣鳞苔属植物分类学面临的一种重要挑战之一。为了鉴定某些形态相同但遗传早已分化的分类单元,我们引入了在其它生物支系的物种界定上已经取得成功的的P(AB)和P(RD)标准。此项对疣鳞苔属植物的系统发育和性状进化的研究为我们进一步研究衍生苔类植物的分类学特别是生活在极端环境的苔类植物的遗传和表型分化,提供了一个很好的范例。更多还原

【Abstract】 Despite substantial evidence based on molecular data greatly improved our understanding of plant taxonomy and systematics, the species of bryophyte were defined mainly on morphological evidence in current bryophyte taxonomy. Recent molecular studies have indicated that the phylogenetic relationship of derived liverworts lineages can’t be recovered based only on morphology as well as species delimitation. Some hypotheses have been suggested, e.g. the conflict between morphological and molecular evidence might result from parallel evolution and/or convergence and occurrence of cryptic species. Particularly for plant lineages growing in extreme habitats, rampant homoplasy of morphological characters have been frequently recovered in context of the stabilizing selection imposing by extreme habitats. Cololejeunea is one of the largest genera in derived liverworts, with preferrablely growing in epiphyllous habitats. Thus, we hypothesized that morphological-typological species (MTSs) concept could not be used to identify the real extent species in context of limited mophorspace and extreme habitat. Here we used three approaches to explore evidence of phenotypic evolution of Cololejeunea. Firstly, we explored evidences of rampnt homoplasy of morphological characters commonly used in Cololejeunea taxonomy using phylogenetic trees reconstructed based on DNA sequences. Secondly, we inferred the correlation of genetic diversity and morphological disparity. Thirdly, we used DNA taxonomy to compare the number of species defined either by morphology or by genetic distinctiveness based on chloroplast and nuclear markers. The results are as follow:(1) We firstly constructed a comprehensive phylogeny of Cololejeunea and relative genera based on132accessions and three gene regions (rbcL, trnL-F, and nrITS). The molecular data support three major lineages: Colura, Myriocoleopsis, and Cololejeunea. Myriocoleopsis species were resolved in a clade with Cololejeunea minutissima. Aphanolejeunea and Chondriolejeunea were both resolved as putative monophyletic groups, and nested in the Cololejeunea clade. The clade comprising of Cololejeunea angustiflora and Cololejeunea magnilobula was found to be sister to the clade comprising the remaining Cololejeunea species. Currently accepted subgenera of Cololejeunea were paraphyletic or polyphyletic. Seven out of31morphological-based species with two or multiple accessions were not supported as natural taxa. The results found evidence to support the rampant homoplasy of morphological characters used in Cololejeunea taxonomy, which could be used to explain a sum of arguments on Cololejeunea classification based on morphology only. Our data did not provide evidence for ancient vicariance events where major clades and continents were associated, instead some evidence was recovered for recent intercontinental species range expansion.(2) To infer the correlation between phylogenetic and phenotypic distance matrix, the morphological characters/traits distance matrix was generated based on70Cololejeunea MTSs and13gametophyte and life history characters/traits. Whereas, the phylogenetic relatedness were qualified by Patristic and Hamming distance based on three gene markers (rbcL, trnL-F, and nrITS). The result of Mantel test indicated that there was strong correlation between9gametophyte characters and phylogenetic distance matrices, while no phylogenetic signals were discovered in life history relevant traits might resulting from rampant convergence of this characters morphological characters or random phenotypic drift. It is assumed that the degree of phenotypic disparity of characters varies within characters as well as clades. Thus special attentions should be paid on the selection of morpholoigal characters for taxonomy.(3) We studied the occurrence of cryptic species in Cololejeunea lanciloba complex. The DNA taxonomy was applied to calculate the genetic distinctness using the statistic measures of species delimitation. We used two variable region markers(trnL-F and nrITS) and62accessions.We found evidence of13molecular operational taxonomy units with genetic differentiation rather than four MTSs in C. lanciloba complex of interest, suggesting the occurrence of cryptic species in this complex. The accessions of one MTS were nested in more than one clade, while some clades included multiple phenotypes, supporting the limited morphological disparity in some clades whereas occurrence of plasticity in other clades. In this study we compared the approaches of species delimitation based on long-stand monophly and paraphyly and P (AB) and P (BD). The P (AB) and P (BD) measures were proved to be more sensitive to genetic differentiation. As we knew, this was the first time to apply statistic measures in species delimitation. Furthermore, the feasibility of Boykin "tip-to-root" iterative methods in species identification was proved.In total, we constructed a comprehesively phylogeny of Cololejeunea and its closely relatives, outlined the taxonomic frame of this genus, solved several problems of genera and subgenera classification. In the study of phenotypic evolution of morphological characters incorporated with phylogenetic trees, we found the evidence of rampant homoplasy might as a result of stabilizing selection exporting by epiphyllous habitat and limited development options. Rampant homoplasy of morphological characters could be used to explain the occurance of observed correlation between phenotypic and phylogenetic divergences in several clades of Cololejeunea. Cryptic species is one of important challenges for Cololejeunea taxonomy. We used P (AB) and P (RD) measures successfully worked in the species delineation of other organism lineages to delimitate species with genetic distinctiveness and morphological uniformity in Cololejeunea. This study of phenotypic evolution and phylogeny of Cololejeunea was a good model to evoke the future taxonomic work on other derived liverworts particularly for lineages in extreme habitats.更多还原