The evolutionary position of nematodes.
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.


CONCLUSIONS
We conclude that insects (arthropods) are genetically and evolutionarily closer to humans than to nematode worms.
Blair
Jaime E
JE
Astrobiology Research Center and Department of Biology, The Pennsylvania State University, University Park, PA 16802, USA. jeb322@psu.edu
Ikeo
Kazuho
K
Gojobori
Takashi
T
Hedges
S Blair
SB
D000818:Animals; D015982:Bias; D017173:Caenorhabditis elegans / Q000145:classification* / Q000235:genetics*; D004331:Drosophila melanogaster / Q000145:classification / Q000235:genetics; D019143:Evolution, Molecular; D006801:Humans; D008954:Models, Biological; D009154:Mutation; D009687:Nuclear Proteins / Q000235:genetics; D010802:Phylogeny
D009687:Nuclear Proteins