Eumycetozoans and molecular systematics F.W. Spiegel, S.B. Lee, and S.A. Rusk Abstract: Eumycetozoans, the myxomycetes, protostelids, and dictyostelids, were first hypothesized to be a monophyletic group by L.S. Olive, who suggested that the primitive members of the group were similar to some of the extant protostelids. A review of morphological evidence supporting some aspects of this hypothesis is presented along with explicit explanations of the shortcomings of morphological data as tests of other aspects. For the hypothesis to be supported, modified, or rejected, data from other areas such as the sequences of the nuclear ribosomal small subunit genes (SSrDNA) will have to be used. Presently, sequences for this gene are known only from Physarum polycephalum and Dictyostelium discoideum. These two slime molds are treated as separate, deep clades in the grand eukaryote phylogenies derived from the sequences of SSrDNA. That is, each species represents an independent lineage that diverged early in the history of the eukaryotes. Insufficient taxon sampling may account for the molecular trees which suggest that the dictyostelids and myxomycetes are not members of a monophyletic group. We have begun to examine the SSrDNA sequence in the protostelid Protostelium mycophaga. Preliminary phylogenetic reconstructions using 11 eukaryotic outgroups suggest that the protostelids, myxomycetes, and dictyostelids are members of a single monophyletic group which may be most closely related to the Chromista. It is interesting that these results coincide with earlier phylogenetic hypotheses based on the morphological characters of these slime molds. Key words: dictyostelids, myxomycetes, protostelids, ribosomal DNA, slime molds. Resume : Les eumycCtozoens, les myxomycbtes, les prostClides et les dictyostClides ont CtC, dans une premibre hypothbse, considCrCs comme un groupe monophylCtique par L.S. Olive, qui a suggCrC que les membres primitifs de ce groupe seraient semblables ii certains protostClides actuels. L'auteur prCsente une revue des preuves morphologiques qui supportent certains aspects de cette hypothbse, ainsi que des explications des insuffisances de donnCes morphologiques pour en Cvaluer d'autres aspects. Pour supporter, modifier ou rejeter l'hypothbse, des donnCes provenant d'autres sources, telles que les sCquences des gtnes de la petite sous-unit6 de 1'ADN ribosomal nuclCique (SSrADN) devront Ctre utilistes. PrCsentement, les sCquences de ces gbnes ne sont connues que chez le Physarum polycephalum et le Dictyostelium discoideum. Ces deux myxomycbtes sont traitts comme des clades profonds et distincts dans la grande phylogCnie des eucaryotes, dCrivCe des sequences du SSrADN. Ceci signifie que chaque espbce constitue une IignCe indkpendante qui a tres t6t divergC au cours de I'histoire des eucaryotes. Un Cchantillonage insuffisant des taxons peut expliquer les dendrogrammes molCculaires qui suggtrent que les dictyostClides et les myxomycttes seraient des membres d'un m&megroupe phylogCnCtique. L'auteur a commencC ii examiner la sCquence du SSrADN du protostClide Protostelium mycophaga. Des reconstructions phylogCnCtiques prkliminaires utilisant 11 groupes d'eucaryotes distincts suggbrent que les protostClides, les myxomycbtes et les dictyostClides seraient des membres d'un seul groupe phylogCnCtique qui serait peut Stre Ctroitement liC aux chromista. I1 est intCressant que ces rCsultats coincident avec les premibres hypothbses basCes sur les caractbres morphologiques des champignons visqueux. Mots cl&s : dictyostClides, myxomycbtes, protostClides, ADN ribosomal, champignons visqueux. [Traduit par la rCdaction] Received August 15, 1994. F.W. Spiegel.' Department of Biological Sciences, University of Arkansas, Fayetteville, AR 72701, U.S.A. S.B. LeeZ and S.A. Rusk. Department of Biological Sciences, University of Northern Colorado, Greeley, CO 80639, U.S.A. ' Author to whom all correspondence should be addressed. Present address: DNA Laboratory, Bureau of Forensic Services, California Department of Justice, 626 Bancrofi Way, Berkeley, CA 94701, U.S.A. Introduction When an evolutionary lineage splits, the daughter lineages subsequently follow their own, independent histories. Hen- nig (1966), among others, has pointed out this fundamental but often underappreciated principle of phylogenetic sys- tematics. When we try to determine the phylogenetic rela- tionships between groups of organisms, we are looking for clues to their shared history prior to their divergence. HOW- ever, it can be the case that these clues are hidden or lost because of events in their lineages' independent histories. Can. J. Bot. 73(Suppl. 1): S738-S746 (1995). Printed in Canada I ImprimC au Canada Can. J. Bot. Downloaded from www.nrcresearchpress.com by Renmin University of China on 06/04/13 For personal use only.