Eumycetozoans and molecular systematics

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.

The Revised Classification of Eukaryotes

“…), consisting of a long, anteriorly directed cilium, extending from BB2 (terminology of Andersen et al. , Spiegel , Spiegel et al , and Wright et al ), a reflexed cilium extending from BB1 and lying in a ventral groove, microtubular rootlets 3 and 4 associated with BB2 – rootlet 3 forming an open cloak of microtubules that is arranged in a left‐handed spiral in cross section and rootlet 4 as a band of microtubules that arises orthogonally to rootlet 3 and extends along the left side of the groove, microtubular rootlets 1 and 2 associated with BB1 – rootlet 1 as a band of microtubules associated with a nonmicrotubular posterior parakinetosomal structure (Wright et al ) and rootlet 2 as a band of microtubules parallel to BB1, with rootlets1 and 2 extending along the right side of the groove, MTOC with a cone array extending from a stalk associated with the basal end of BB2 (many taxa have cells with some of these elements missing); several nonmicrotubular elements may also be present. Although most members of the supergroup have stages of the life cycle that exhibit amoeboid motion and feeding, the morphology of the amoeboid cells is so variable that it is impossible to determine if all amoebae in the group are homologues of each other.…”

“…Although most members of the supergroup have stages of the life cycle that exhibit amoeboid motion and feeding, the morphology of the amoeboid cells is so variable that it is impossible to determine if all amoebae in the group are homologues of each other. It is unlikely that they are not (Spiegel et al ). Many taxa have more than one amoeboid state in the life cycle.…”

Origin and evolution of the slime molds (Mycetozoa)

“…Thus, inclusion of additional rRNA sequences from all three classes of Mycetozoa, especially protostelids, might help to resolve some of these questions. This is suggested by the results of Spiegel et al (41), who analyzed the first protostelid molecular sequence, a 310-nucleotide portion of the SSU rRNA gene of Protostelium mycophaga. Analyses of this sequence with a limited set of taxa showed strong support for a monophyletic Mycetozoa, although the method of sequence alignment may have biased the results in this direction (41).…”

Check-list of microscopic protosteloid amoebae from the Southwest of Europe

“…2004), where they take part as predators feeding also upon other decomposers such as yeasts, and filamentous fungi (Olive, 1975;Whitney & Bennett, 1984). These organisms were traditionally classified as occupying a primitive position within the group of slime molds termed Eumycetozoa, that also includes the myxomycetes and the dictyostelids (Olive, 1975;Spiegel, 1986;Spiegel Lee & Rusk, 1995;Baldauf & Doolittle, 1997), but recent molecular data suggest that protosteloid amoebae are polyphyletic and they belong to different groups of Amoebozoa (Shadwick & al., 2009b;Fiore-Donno & al., 2010;Lahr & al., 2011;Adl & al., 2012), not necessarily directly related to other eumycetozoans.…”