1. Institute of Cell, Animal and Population Biology, King's Buildings, University of Edinburgh, Edinburgh EH9 3JT, UK
2. Department of Morphology, Systematics and Ecology, University of Gent, B-9000 Gent, Belgium
3. International Institute of Parasitology, St Albans AL4 0XU, UK
4. Department of Biological Sciences, University of South Florida, Tampa, Florida 33620, USA
5. Harvard-Thorndike Laboratory, Department of Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts 02215, USA
6. NemaPharm, Inc, 26 Landsdowne Street, Cambridge, Massachusetts 02139, USA
7. Department of Molecular Physiology and Biophysics, Baylor College of Medicine, Houston, Texas 77030, USA
8. Division of Molecular Biology and Biochemistry, School of Biological Sciences, University of Missouri, Kansas City, Missouri 64110, USA

Correspondence to: Mark L. Blaxter¹ Correspondence and requests for materials should be addressed to M.L.B. (e-mail: Email: mark.blaxter@ed.ac.uk).

Abstract

Nematodes are important: parasitic nematodes threaten the health of plants, animals and humans on a global scale¹,²; interstitial nematodes pervade sediment and soil ecosystems in overwhelming numbers³; and Caenorhabditis elegans is a favourite experimental model system⁴. A lack of clearly homologous characters and the absence of an informative fossil record have prevented us from deriving a consistent evolutionary framework for the phylum. Here we present a phylogenetic analysis, using 53 small subunit ribosomal DNA sequences from a wide range of nematodes. With this analysis, we can compare animal-parasitic, plant-parasitic and free-living taxa using a common measurement. Our results indicate that convergent morphological evolution may be extensive and that present higher-level classification of the Nematoda will need revision. We identify five major clades within the phylum, all of which include parasitic species. We suggest that animal parasitism arose independently at least four times, and plant parasitism three times. We clarify the relationship of C. elegans to major parasitic groups; this will allow more effective exploitation of our genetic and biological knowledge of this model species.

1. Institute of Cell, Animal and Population Biology, King's Buildings, University of Edinburgh, Edinburgh EH9 3JT, UK
2. Department of Morphology, Systematics and Ecology, University of Gent, B-9000 Gent, Belgium
3. International Institute of Parasitology, St Albans AL4 0XU, UK
4. Department of Biological Sciences, University of South Florida, Tampa, Florida 33620, USA
5. Harvard-Thorndike Laboratory, Department of Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts 02215, USA
6. NemaPharm, Inc, 26 Landsdowne Street, Cambridge, Massachusetts 02139, USA
7. Department of Molecular Physiology and Biophysics, Baylor College of Medicine, Houston, Texas 77030, USA
8. Division of Molecular Biology and Biochemistry, School of Biological Sciences, University of Missouri, Kansas City, Missouri 64110, USA

Correspondence to: Mark L. Blaxter¹ Correspondence and requests for materials should be addressed to M.L.B. (e-mail: Email: mark.blaxter@ed.ac.uk).