Molecular Phylogeny of the Arthropoda and the "Ecdysozoa" Hypothesis

我们的项目旨在阐明节肢动物之间的关系及其在后生动物中的系统发育地位。在重点项目1174的框架内，我们已经对五个节肢动物物种的约28,000个EST(表达序列标签)进行了测序。提取了同源基因，并与优先项目的其他小组合作，进行了大规模的节肢动物关系系统学研究(117个物种，129个基因[37,476个位置])。454条蝎子EST的焦磷酸测序(~428,000个读数；~100 Mb)表明，该方法适用于系统发育研究。基于单基因，我们推测海蜘蛛是真丝虫的姊妹群，并发现雷米足纲和六足纲的亲缘关系出乎意料地密切。然而，节肢动物系统发育的基本问题仍然没有解决(例如，多足动物的位置)。我们将继续通过多基因分析来阐明节肢动物的系统发育。454焦磷酸测序将产生来自两个多足类和两个螯合类物种的EST。当cDNA归一化显示有足够质量的单基因增加时，我们将对每个物种进行454次半平板操作，并添加来自迟发性和显性杂交的EST，以增加蜕殖虫的数据覆盖率。在多基因序列比对的基础上，我们将与其他小组合作研究节肢动物和蜕皮动物的系统发育。我们将特别关注多足纲(Mandibuata vs.Myriochelata)的位置以及海龟纲和多足纲之间的关系，考虑外群选择、不同的进化速度和碱基组成等影响。分子钟法将被用来估计选定节肢动物之间的分歧时间。此外，血蓝蛋白和其他选定的基因将被用来推断某些类群之间的关系。

Our project aims at the elucidation of the relationships among arthropods and their phylogenetic position in the Metazoa. Within the framework of the priority project 1174, we have sequenced ~28,000 ESTs (expressed sequence tags) from five arthropod species. Orthologous genes were extracted and a large scale phylogenomic approach (117 species, 129 genes [37,476 positions]) of arthropod relationships was conducted in cooperation with other groups of the priority project. A 454 pyrosequencing approach of scorpion ESTs (~428,000 reads; ~100 Mb) showed that this method is suitable for phylogenomic research. Based on single genes, we inferred that sea spiders (Pycnogonida) are the sister-group of Euchelicerata and found an unexpectedly close relationship of Remipedia and Hexapoda. Nevertheless, essential questions of arthropod phylogeny are still unresolved (e.g., position of Myriapoda). We will continue with the elucidation of arthropod phylogeny by mutigene analyses. ESTs from two myriapod and two chelicerate species will be generated by 454 pyrosequencing. When normalisation of cDNA shows an increase of single genes with sufficient quality, we will perform 454 runs of half plates per species and add ESTs from a tardigrade and a kinorhynchan to increase data coverage in Ecdysozoa. Based on concatenated multigene alignments, we will study arthropod and ecdysozoan phylogeny in cooperation with other groups. We will specifically focus on the position of the Myriapoda (Mandibulata vs. Myriochelata hypotheses) and the relationship among chelicerate and myriapod classes, considering effects like outgroup selection, variable evolution rates and base compositions. Molecular clock methods will be used to estimate divergence times between selected arthropods. In addition, hemocyanin and other selected genes will be used to infer the relationships among certain taxa.