【作者】 龚迎春；

【导师】 余育和；

【作者基本信息】 中国科学院研究生院（水生生物研究所） ， 水生生物学， 2007， 博士

【摘要】 车轮虫是一类具有独特附着盘结构,且可自由运动的寄生性原生动物。目前,有关该类群的研究仍集中于形态学与区系方面,而关于它们的系统发育研究却相对滞后。本文结合形态学和分子生物学两种技术手段,探究了车轮虫种属间的相互关系及其在寡膜纲中的系统分类地位,并比较分析了基于形态特征和分子标记所构建系统树拓扑结构的差异。1.车轮虫形态特征的系统发育学研究。首次提出齿体特征量化法,并应用于车轮虫属间亲缘关系研究。结果显示,车轮虫科内各属的进化路线为:壶形虫属→两分虫属→小车轮虫属和三分虫属→高纤虫属、纤车轮虫属、旋带虫属、半车轮虫属、拟车轮虫属和车轮虫属→偏车轮虫属。我们还讨论了齿体的进化趋势,并认为齿体是车轮虫的衍征,齿体的变化可以反映车轮虫的进化趋势。2.车轮虫分子标记的系统发育学研究。测定了6种车轮虫的SSUrRNA基因序列和3种车轮虫的αTubulin基因序列,分别构建邻接树、最大简约树、最大似然树和贝叶斯树,并探讨了以车轮虫为代表的游走类纤毛虫在寡膜纲中的系统发育地位。所构建分子系统发育树都显示游走类纤毛虫没有和固着类纤毛虫聚在一起,从而证明缘毛类纤毛虫不是单系类群。我们认为缘毛类纤毛虫的两大类群——游走类纤毛虫和固着类纤毛虫,形态上的相似可能是由于趋同进化引起的。不过缘毛类纤毛虫也有可能是一个单系类群,由于“长枝吸引”或者采样不足,使得我们所构建的分子系统树不能真实反映两个类群间的关系。由于目前还不能排除长枝吸引和采样不足的影响,缘毛类纤毛虫作为寡膜纲的一个亚纲的分类地位需要进一步的验证。3.车轮虫形态特征和分子标记的系统发育研究比较。我们测定了4种车轮虫的ITS1基因序列,并采用齿体特征量化法得到这4种车轮虫的特征量化值。通过比较基于分子数据与形态数据构建的亲缘关系树的异同,发现基因树和形态树可以较好地吻合,说明在本论文中提出的齿体特征量化法,对于研究车轮虫内部的亲缘关系是可行的。更多还原

【Abstract】 Trichodinids (Ciliophora: Peritrichida) are one of the most common parasiticprotozoan,which have special structure of adhesive disc, and can swim freely. At thepresent time, studies on trichodinids still concern mainly with their taxonomyespecially with re-investigating or re-describing the old species using moderntechniques, and very little attention has been given to the phylogenetic relationshipsof these ciliates. In this dissertation, we studied the phylogeny of trichodinids withboth morphological and molecular markers, and compared the topologies of the twokindsoftrees.1. Phylogenetic relationships among trichodinids derived from the characteristicvalues of denticles. A quantitative method to illustrate denticlating characters werefirstly introduced and applied to the phylogenetic studies among genera ofTrichodinidae.Theresultsshowedthatthetrichodinidsevolvedasthefollowingtrend:Urceolaria→Dipartiella→(Trichodinella, Tripartiella)→(TrichdoxaPallitrichodina, Vauchomia, Semitrichodina, Paratrichodina, Trichodina)→Hemitrichodina. We also discussed the evolutionary trend of the denticles andconcluded that the denticles of the adhesive disc should be an apomorphic feature ofthe trichodinids and their changes could reflect the evolutionary tendencies of these ciliates.2. Molecular phlogenetic studies among trichodinids. SSU rRNA complete genesequences of 6 species of trichodinids, andαTubulin partial gene sequences of 3species of trichodinids, were sequenced. Then, the neighbor joining, maximumparsimony, maximum likelihood,and Bayesiantrees for thetwo gene sequences wereconstructed separately. All the trees showed that the mobilines represented bytrichodinids did not cluster with their related species, sessilines. Therefore, theperitrichs were proved to be not a monophyletic group. We considered that thesimilarity of morphology of mobilines and sessilineswere the results of evolutionaryconvergence. However, maybe the peritrichs are really monophyly, and either/bothlong-branchattractionor under-samplingmadean artifactual recoveryofmobilines inthe phylogenetic trees. Because we could not exclude the disturbance of thelong-branch attraction or under-sampling in the present study, the position of theperitrichsintheclassOligohymenophoreaneedstobestudiedfurther.3. Comparative study between morphological and molecular phylogeny oftrichodinids. ITS1 gene sequences of four species of trichodinids were sequenced toconstruct phylogenetic tree, and the characteristic values of denticles werecalculated to generate dendrogram. By comparison the two trees, their topologieswerefoundtobesimilar.Therefore,the quantitativemethodtoillustratedenticlatingcharacters was proved to be feasible to study the phylogenetic relationship amongtrichodinids.更多还原