Research article

The evolutionary position of nematodes

Jaime E Blair¹ , Kazuho Ikeo² , Takashi Gojobori² and S Blair Hedges¹

¹Astrobiology Research Center and Department of Biology, The Pennsylvania State University, University Park, PA 16802, USA

²Center for Information Biology, National Institute of Genetics, Mishima, Shizuoka-ken 411-8540, Japan

author email corresponding author email

BMC Evolutionary Biology 2002, 2:7doi:10.1186/1471-2148-2-7

Published:	8 April 2002

Abstract

Background

The complete genomes of three animals have been sequenced by global research efforts: a nematode worm (Caenorhabditis elegans), an insect (Drosophila melanogaster), and a vertebrate (Homo sapiens). Remarkably, their relationships have yet to be clarified. The confusion concerns the enigmatic position of nematodes. Traditionally, nematodes have occupied a basal position, in part because they lack a true body cavity. However, the leading hypothesis now joins nematodes with arthropods in a molting clade, Ecdysozoa, based on data from several genes.

Results

We tested the Ecdysozoa hypothesis with analyses of more than 100 nuclear protein alignments, under conditions that would expose biases, and found that it was not supported. Instead, we found significant support for the traditional hypothesis, Coelomata. Our result is robust to different rates of sequence change among genes and lineages, different numbers of taxa, and different species of nematodes.

Conclusion

We conclude that insects (arthropods) are genetically and evolutionarily closer to humans than to nematode worms.