Molecular Phylogeny of the Arthropoda and the "Ecdysozoa" Hypothesis

本研究旨在阐明节肢动物之间的亲缘关系及其在后生动物中的系统发育位置。在优先项目1174的框架内，我们对来自五种节肢动物的约28，000个EST（表达序列标签）进行了测序。与优先项目的其他小组合作，提取了节肢动物关系的直系亲属基因，并进行了大规模的直系亲属基因组方法（117个物种，129个基因[37，476个位点]）。蝎EST的454焦磷酸测序方法（~ 428，000 reads; ~100 Mb）表明该方法适用于蝎基因组研究。基于单基因的研究，我们推测密子目蜘蛛是真螯角类的姐妹类群，并发现了六足类与残足类的亲缘关系。然而，节肢动物生殖的基本问题仍然没有解决（例如，（Myriapoda）。我们将继续通过多基因分析阐明节肢动物的生殖发育。将通过454焦磷酸测序产生来自两种多足动物和两种螯合动物物种的EST。当cDNA的归一化显示具有足够质量的单个基因的增加时，我们将对每个物种进行454次半板运行，并添加来自缓步动物和动喙动物的EST以增加蜕皮动物的数据覆盖率。基于串联多基因比对，我们将与其他群体合作研究节肢动物和蜕皮动物的生殖发育。我们将特别关注的位置的多足类（Mandibulata与Myriochelata假说）和螯形类和多足类之间的关系，考虑外群选择，变量的进化速率和基础成分的影响。分子钟方法将用于估计选定的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.