First Genome-Scale Evidence Supporting Ecdysozoa

DOPAZO H. AND J. DOPAZO

Marseilles, Francia

Jornada; 8th Evolutionary Biology Meeting at Marseilles; 2004

There are many reasons to consider the coelomata-ecdysozoa problem the most astonishing issue in animal systematics and one of the major open ended subjects in evolutionary biology. Previous single gene and genome scale analyses designed to define the issue contradicted each other. The recently completed sequences of several eukaryotic genomes provide an enormous amount of comparative data to address conflicting evolutionary hypothesis. Here, we present the first evidence obtained from a genome scale analysis supporting the ecdysozoa hypothesis. Through the most extensive phylogenomic analysis carried out to date complete genomes of 11 eukaryotic species have been scanned in order to find homologous sequences derived from 18 human chromosomes. More than 140,000 amino acid sequences corresponding to the exons of more than 14,000 genes were scanned. Finaly, only a carefully selected number of sequences ranged from ~1,000 to ~400 were concatenated in 8 different data sets showing a gradual decrement of the nematode - arthropods mean distance. Distance and maximum-likelihood methods of phylogenetic reconstruction were assayed. Relative rate test using a phylogenetic weighted scheme of outgroups was used to define data sets fitting clock-like behaviour. By gradualy decreasing the relative branch length of the nematode species, the bootstrap support and the statistical tree likelihood confidence changed from coelomata to ecdysozoa. The reliability of the ecdysozoa, grouping arthropods and nematodes in a single clade was unequivocally accepted in data sets where traces of long branch attraction effect were removed.We demostrate that using a genome wide approach the new animal phylogeny can be statistically supported.