RUI: Molecular Phylogeny of Gymnolaemate Bryozoans

苔藓虫（外生虫科）是一门广泛分布于全球海洋和淡水底栖动物栖息地的群居动物。很容易看到的群落是由数百或数千种微小的动物组成的，每一种都不到一毫米长。据估计，现存物种有6000种，已描述的化石物种超过15000种。现存苔藓虫种类最多的类群是Gymnolaemata纲，目前分为两目：Ctenostomata和Cheilostomata。栉齿动物有未钙化壁的类动物，而唇齿动物有钙化壁。绝大多数现存的苔藓虫物种都是唇口动物，它们自大约1.45亿年前出现以来经历了巨大的辐射。由于其广泛的化石记录、丰富的多样性和广泛的分布，唇口动物在进化和生态学研究中具有非常重要的意义。然而，对这些研究的正确解释取决于对舌口动物之间进化关系的可靠认识。由于性状之间的高度趋同，利用形态特征重建这种系统发育是非常困难的。为了解决这个问题，本研究将收集苔藓虫的DNA序列数据，并进行分支分析以重建系统发育。利用线粒体大亚基16S rRNA基因的部分序列进行的初步研究表明，掌口动物的系统发育可能是复杂的，并且与更广泛的对裸子动物系统发育的考虑密不可分。本研究的目的是：1)利用核18S rRNA基因序列在更高水平苔藓动物系统发育的背景下确定裸子苔藓动物是否为单系类群，并重建舌口和舌口苔藓动物之间的更高水平关系；2)利用18S rRNA基因和线粒体16S rRNA基因的序列数据重建舌口动物之间的超家族关系。

9806368 Dick The Bryozoa (Ectoprocta) comprise a phylum of colonial animals broadly distributed worldwide in marine and freshwater benthic habitats. Colonies, which are readily visible, are composed of hundreds or thousands of tiny zooids, each less than a millimeter long. There are an estimated 6,000 living species and over 15,000 described fossil species. The largest group containing living bryozoan species is the class Gymnolaemata, currently divided into two orders: Ctenostomata and Cheilostomata. Ctenostomes have zooids with uncalcified walls, whereas cheilostomes have calcified walls. The large majority of living bryozoan species are cheilostomes, which have undergone a great radiation since their appearance approximately 145 million years ago. Because of their extensive fossil record, considerable diversity, and broad distribution, cheilostomes have been very important in evolutionary and ecological studies. However, correct interpretation of these studies depends upon a reliable knowledge of evolutionary relationships among cheilostomes. Reconstructing this phylogeny using morphological characters has been exceedingly difficult, due to high levels of convergence among characters. To begin to remedy this problem, this study will gather DNA sequence data from bryozoans and perform cladistic analyses to reconstruct phylogeny. Preliminary work utilizing a partial sequence of the mitochondrial, large-subunit 16S rRNA gene has suggested that cheilostome phylogeny is likely to be complex, and inseparable from a broader consideration of gymnolaemate phylogeny. The goals of this study are 1) to utilize sequences from the nuclear 18S rRNA gene to determine whether the Gymnolaemata are a monophyletic group in the context of a higher-level bryozoan phylogeny, and to reconstruct higher-level relationships among ctenostome and cheilostome bryozoans, and 2) to utilize sequence data from both the 18S rRNA gene and the mitochondrial 16S rRNA gene to reconstruct superfamily- level relationships among cheilostomes.