The Trophic Cells of Clastostelium Recurvatum, a Third Member of the Myxomycete-Like Protostelids

Molecular phylogenetic analyses support the validity of Ceratiomyxa porioides (Amoebozoa, Eumycetozoa) at species level

The frequently encountered macroscopic slime molds of the genus Ceratiomyxa have long been recognized by mycologists and protistologists for hundreds of years. These organisms are amoebozoan amoebae that live and grow inside and on the surface of decaying wood. When conditions are favorable, they form subaerial sporulating structures called fruiting bodies which take on a variety of forms. These forms are typically some arrangement of column and/or branches, but one is uniquely poroid, forming folds instead. Originally, this poroid morphology was designated as its own species. However, it was not always clear what significance fruiting body morphology held in determining species. Currently, Ceratiomyxa fruticulosa var. porioides, the poroid form, is considered a taxonomic variety of Ceratiomyxa fruticulosa based on morphological designation alone. Despite its long history of observation and study, the genus Ceratiomyxa has been paid little molecular attention to alleviate these morphological issues. We have obtained the first transcriptomes of the taxon C. fruticulosa var. porioides and found single gene phylogenetic and multigene phylogenomic support to separate it from C. fruticulosa. This provides molecular evidence that fruiting body morphology does correspond to species level diversity. Therefore, we formally raise Ceratiomyxa porioides to species level.

Eumycetozoans and molecular systematics

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.