SGER: A Multi-Gene Approach to Understanding Relationships Among Ciliates in the Class Spirotrichea

Laura a . Katz博士获得了一项资助，研究一种被称为纤毛虫的迷人微生物的进化。纤毛虫是一种多样化的原生动物，其特征是每个细胞中存在两种核，并且它们的染色体具有不同寻常的分子加工过程。与许多植物和动物不同，我们目前只有一个基本的框架来解释这些生物的进化史。例如，在过去的20年里，随着物种鉴定技术的进步，纤毛虫的种类已经从基于显微镜分析的只有3个，到基于电子显微镜的8个，再到基于DNA序列数据的至少9个。螺旋体类代表了一个特别有争议的纤毛虫集合，因为之前的分析提供了不同的图像，哪些纤毛虫属于这个类，以及这些纤毛虫是如何相关的。被认为属于螺旋体纲的纤毛虫可以在淡水和海洋生态系统中找到，它们的特点是纤毛虫的排列多样，有时甚至是戏剧性的。我们目前的分类系统是基于少数分类群的有限数据。要准确地重建这些生物之间的关系，需要对来自纤毛虫全面调查的多个基因进行分析。本研究的总体目标是：(1)确定螺旋体纲纤毛虫的种类，(2)重建这些物种之间的关系。为了实现这些目标，将确定来自螺旋体类潜在成员的三个基因的DNA序列（小亚基rRNA， α -微管蛋白和DNA聚合酶II的最大亚基）。此外，序列将从适当的外群物种（非螺旋体）中进行表征。所得到的DNA序列将使用至少两种比对方法进行比对，物种关系的估计将使用几种系统发育方法（例如最大简约和最大似然）对单个基因和组合数据集进行比对。由此产生的系谱将回答有关螺旋体进化史的问题，同时也为未来研究纤毛虫之间的关系指明了方向。

DEB-0079325Laura A. Katz Dr. Laura A. Katz has been awarded a grant to study the evolution of a fascinating type of microorganisms known as ciliates, a diverse group of protozoa characterized by the presence of two types of nuclei in each cell and by unusual molecular processing of their chromosomes. Unlike many plants and animals, we currently have only a basic framework for interpreting the evolutionary history of these organisms. For example, in the past twenty years, as techniques for identifying species have improved, the number of classes of ciliates has risen from only three based on microscopic analyses, to eight based on electron microscopy, to at least nine based on DNA sequence data. The class Spirotrichea represents a particularly contentious assemblage of ciliates as previous analyses provide varying pictures of which ciliates belong within this class and how these ciliates are related. Ciliates thought to belong to the class Spirotrichea can be found in both freshwater and marine ecosystems, and are characterized by diverse, and sometimes dramatic, arrangements of their ciliature. Our current classification system is based on limited data from only a handful of taxa. Analysis of multiple genes from a comprehensive survey of ciliates is needed to accurately reconstruction relationships among these organisms. The overall goals of this study are (1) to identify species of ciliates that belong to the class Spirotrichea, and (2) to reconstruct relationships among these species. To achieve these goals, DNA sequences will be determined for three genes (small subunit rRNA, alpha-tubulin and the largest subunit of the DNA polymerase II) from potential members of the class Spirotrichea. In addition, sequences will be characterized from appropriate outgroup species (non-spirotrichs). The resulting DNA sequences will be aligned using at least two alignment methods and estimates of species relationships will be made using several phylogenetic methods (e.g. maximum parsimony and maximum likelihood) on both individual genes and a combined data set. The resulting genealogies will answer questions about the evolutionary history of spirotrichs, while also indicating areas for future research on the relationships among ciliates.