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The evolutionary position of nematodes.

Blair JE, Ikeo K, Gojobori T, Hedges SB - BMC Evol. Biol. (2002)

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

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Affiliation: Astrobiology Research Center and Department of Biology, The Pennsylvania State University, University Park, PA 16802, USA. jeb322@psu.edu

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.

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Test of mutational saturation in the four-taxon data set. (A) The mean number of variants per variable site was averaged for ten groups often according to evolutionary rate (vertebrate-arthropod distance = diamonds, nematode branch length = squares). (B) The minimum number of nucleotide changes required for unique nematode variants were also averaged according to evolutionary rate. Trend lines are indicated (solid for vertebrate-arthropod distance, dashed for nematode branch length).
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Figure 4: Test of mutational saturation in the four-taxon data set. (A) The mean number of variants per variable site was averaged for ten groups often according to evolutionary rate (vertebrate-arthropod distance = diamonds, nematode branch length = squares). (B) The minimum number of nucleotide changes required for unique nematode variants were also averaged according to evolutionary rate. Trend lines are indicated (solid for vertebrate-arthropod distance, dashed for nematode branch length).

Mentions: To ensure that this result was not affected by mutational saturation in our data set, the mean number of variants per variable site was determined for each protein and averaged for ten groups of proteins ordered by evolutionary rate (Fig 4A). As predicted, variable sites in the faster evolving proteins showed a higher number of variants than those in slow-evolving proteins. We also examined the minimum number of nucleotide changes required for sites where only the nematode sequence varied (Fig 4B). Slow-evolving proteins showed a smaller number of nucleotide changes required to alter amino acid identity, while faster evolving proteins required more changes. Thus, the nematode sequences in the slow-evolving proteins do not appear to be mutationally saturated.


The evolutionary position of nematodes.

Blair JE, Ikeo K, Gojobori T, Hedges SB - BMC Evol. Biol. (2002)

Test of mutational saturation in the four-taxon data set. (A) The mean number of variants per variable site was averaged for ten groups often according to evolutionary rate (vertebrate-arthropod distance = diamonds, nematode branch length = squares). (B) The minimum number of nucleotide changes required for unique nematode variants were also averaged according to evolutionary rate. Trend lines are indicated (solid for vertebrate-arthropod distance, dashed for nematode branch length).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC102755&req=5

Figure 4: Test of mutational saturation in the four-taxon data set. (A) The mean number of variants per variable site was averaged for ten groups often according to evolutionary rate (vertebrate-arthropod distance = diamonds, nematode branch length = squares). (B) The minimum number of nucleotide changes required for unique nematode variants were also averaged according to evolutionary rate. Trend lines are indicated (solid for vertebrate-arthropod distance, dashed for nematode branch length).
Mentions: To ensure that this result was not affected by mutational saturation in our data set, the mean number of variants per variable site was determined for each protein and averaged for ten groups of proteins ordered by evolutionary rate (Fig 4A). As predicted, variable sites in the faster evolving proteins showed a higher number of variants than those in slow-evolving proteins. We also examined the minimum number of nucleotide changes required for sites where only the nematode sequence varied (Fig 4B). Slow-evolving proteins showed a smaller number of nucleotide changes required to alter amino acid identity, while faster evolving proteins required more changes. Thus, the nematode sequences in the slow-evolving proteins do not appear to be mutationally saturated.

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

View Article: PubMed Central - HTML - PubMed

Affiliation: Astrobiology Research Center and Department of Biology, The Pennsylvania State University, University Park, PA 16802, USA. jeb322@psu.edu

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.

Show MeSH
Related in: MedlinePlus