Evolution and classification of protozoa

Following the contemporary logic that classification need not be arbitrary but will be more informative when taxa are monophyletic and holophyletic, we have used ultrastructural studies to erect testable hypotheses (such as those included in the figure below) about relatedness. We have collaborated with the Molecular Evolution Laboratory (Marine Biological Station, Woods Hole) to test these hypotheses, and some elements - especially the basal parts of the tree - have not survived this process.

The skeletal tree of the mid '90s allowed us also to explore styles of classifying taxa. The acceptance of speculation as a criterion to erect taxa has led to considerable instability. The meanings of many taxonomic terms applied to protozoa are not clear. In part this is because little effort has been made to develop a set of rules by which taxa may be defined. Consequently, taxa are erected without a clear sense of what should be included; and secondly the meaning of the term is allowed to meander through conceptual space. As discussed in the '99 paper, much of this uncertaintly can be avoided. We hold that within the domains of classification and evolution, the taxonomic terms must aim to be unambiguous.

• Edgcombe, V.P., Simpson, A. G. B., Amaral Zettler, L., Nerad, T.A., Patterson, D.J., Holder, M. E. and Sogin, M. L. 2002. Pelobionts are degenerate protists: insights from molecules and morphology. Molecular Biology and Evolution, 19:978-982. 127.
• Leipe, D.D, Wainright, P.O., Gunderson, J.H., Porter, D., Patterson, D.J., Valois, F., Himmerich, S. and Sogin, M.L. (1994). The stramenopiles from a molecular perspective: small subunit rDNA sequences from Labyrinthuloides minuta and Cafeteria roenbergensis. Phycologia 33: 369-377
• Patterson, D.J. (1994). Protozoa, Evolution and Classification. Progress in Protozoology, Proceedings of the IX International Congress of Protozoology, Fischer Verlag, Stuttgart, 1-14.
• Patterson, D. J. (1999). The diversity of eukaryotes. American Naturalist 154: S96-S124.
• Patterson, D.J. and Sogin, M. (1992). Eukaryote origins and protistan diversity. In: Hartman, H. and Matsuno, K. The Origin And Evolution of the Cell. pp 13-46. World Scientific Publishers, New Jersey.
• Wainright, P.O., Patterson, D.J. and Sogin, M.L. (1994). Monophyletic origin of animals: a shared ancestry with fungi. pp 39-53 in Farmborough, D.M. (ed) Molecular Evolution of Physiological processes, Society of General Physiologists Series, No. 49; Rockefeller Press, New York.