Molecular Phylogeny of the Arthropoda and the "Ecdysozoa" Hypothesis

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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.