Elucidation of phylogenetic processes during early evolution of basal Metazoa through the phylogenetic study of both, selected molecular marker genes and EST data

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Phylogenetic relationships of early branching Metazoa and the origin of animal life have been subject to unrelenting controversies since inferences from morphological and molecular analyses are often conflicting. Uncertainty not only surrounds the interrelationships between metazoan phyla (i. e., the relative branchings of Porifera, Cnidaria, Ctenophora, and Bilateria) but also concerns many other systematic levels (e. g., monophyly/paraphyly of Porifera and poriferan classes, evolutionary origin of freshwater sponges, etc.). In addition, the placement of choanoflagellates on the eukaryotic tree remains obscure, even though several studies suggest a close relationship to Metazoa or even consider choanoflagellates as a member of Metazoa. The aim of this renewal proposal is to further address these conflicting hypotheses and also to establish a phylogenetic framework that allows studying metazoan evolution. So far, phylogenetic rDNA analyses have not been able to resolve these conflicts unambiguously. Therefore, we will continue to generate EST data and to sample protein-coding loci of basal Metazoa (including choanoflagellates, sponges, and cnidarians), concentrating on an extensive selection of genes that code for enzymes of metabolic pathways, metazoan specific proteins, and proteins involved in poriferan morphogenesis/spiculogenesis. Since shape and composition of spicules are the basis for sponge classification, it is tempting to consider their genetic background under a phylogenetic point of view. With this combined data we will attempt to extrapolate from gene trees to organismal trees.