Arthropod Molecular Evolution
Here we have investigated the evolutionary relationship among the major groups of invertebrates by comparing the DNA sequences of several genes and morphological characters. In our study we have representative animals from the following arthropod groups: Chelicerata (eg. spiders, ticks and mites), Crustacea (crabs), Myriapoda (millipedes and centipedes) and Hexapoda (insects).
The aim of this project is to integrate molecular and morphological investigations of the relationships of the major arthropod lineages, the Chelicerata, Crustacea, Myriapoda, and Hexapoda using a comprehensive set of sample taxa spanning the phylum's diversity. These relationships are still widely debated. Several recent publications support the traditional hypothesis that the Mandibulata (Crustacea + Myriapoda + Hexapoda) are the sister group to the Chelicerata, with Crustacea being the sister group to the Atelocerata (Myriapoda + Hexapoda). Others support the view that crustaceans are more closely related to chelicerates (and fossil groups such as trilobites). Yet others propose that the Hexapoda + Crustacea forms a monophyletic group or that some major lineages are not monophyletic.
We have published (Colgan et al, 1998) analyses based on two genes not previously employed in arthropod phylogenetics: Histone H3 and the small nuclear ribonucleic acid U2 (Download
). Dr Gowrie Thampapillai has collected data for cytochrome oxidase I for almost all of the critical taxa. These will be published in the near future.
The H3 and U2 data are not by themselves sufficient to clarify major arthropod group relationships. The best molecular trees, based on combined analyses of all taxa differ substantially from morphology based trees, although anomalous groupings are usually only weakly supported. Combined analyses of both genes improves congruence with morphological groupings over either gene by itself. A paper reporting combined analyses of morphological and the H3 and U2 molecular data is in press in the journal Cladistics. Once the Cox I data are published, we will combine our three data sets with all available genetic and morphology data sets for a synthetic analysis of arthropod relationships.
Acknowledgements
Funding for this project has been provided by the Australian Museum and the Ken Myer bequest to the Evolutionary Biology Unit.
Participants
Don Colgan
Anne McLauchlan
Buz Wilson
Greg Edgecombe
Gowrie Thampapillai
Julie Macaranas
Sue Livingston
Gerry Cassis
Mike Gray
Selected references
- Aguinaldo, A. M. A., Turbeville, J. M., Linford, L. S., Rivera, M. C., Garey, J. R., Raff, R. A., and Lake, J. A. (1997). Evidence for a clade of nematodes, arthropods and other moulting animals. Nature 387, 489-492.
- Boore, J. L., Collins, T. M., Stanton, D., Daehler, L. L., and Brown, W. M. (1995). Deducing the pattern of arthropod phylogeny from mitochondrial DNA rearrangements. Nature 376, 163-165.
- Edgecombe, G.D. (ed.) (1998). 'Arthropod Fossils and Phylogeny' (Columbia University Press: New York.)
- Fortey, R. A., and Thomas, R. H. (Eds.) (1997). 'Arthropod Relationships'. Systematics Association Special Volume Series 55. (Chapman and Hall: London.)
- Giribet, G., Carranza, S., Baguñà, J., Ruitort, M., and Ribera, C. (1996). First molecular evidence for the existence of a Tardigrada + Arthropoda clade. Molecular Biology and Evolution 13, 76-84.
- Regier, J. C., and Shultz, J. W. (1997). Molecular phylogeny of the major arthropod groups indicates polyphyly of crustaceans and a new hypothesis for the origin of hexapods. Molecular Biology and Evolution 14, 902-913.
- Wheeler, W. C., Cartwright, P., and Hayashi, C. Y. (1993). Arthropod phylogeny: A combined approach. Cladistics 9, 1-39.
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