Dictyostelium Discoideum - Classification and Phylogeny

Classification and Phylogeny

In older classifications, Dictyostelium was placed in the defunct polyphyletic class Acrasiomycetes. This was a class of cellular slime molds, which was characterized by the aggregation of individual amoebae into a multicellular fruiting body, making it an important factor that related the acrasids to the dictyostelids.

More recent genomic studies have shown that Dictyostelium has maintained more of its ancestral genome diversity than plants and animals, although proteome-based phylogeny confirms that amoebozoa diverged from the animal–fungal lineage after the plant–animal split. Subclass Dictyosteliidae, order Dictyosteliales is a monophyletic assemblage within the Mycetozoa, a group that includes the protostelid, dictyostelid, and myxogastrid slime molds. Elongation factor-1α (EF-1α) data analyses support Mycetozoa as a monophyletic group even though rRNA trees place it as a polyphyletic group. Further, these data support the idea that the dictyostelid and myxogastrid are more closely related to each other than they are the protostelid. EF-1α analysis also placed the Mycetozoa as the immediate outgroup for the “animal-fungal clade. Though not strongly supported, there is evidence that Mycetozoa are crown eukaryotes, more closely related to animals and fungi than are the green plants. The multicellularity of the dictyostelid evidences its relationship to animals. Comparing specific amino acid sequences of eight proteins from D. discoideum to those of their homologs in bacteria, yeast, and other eukaryotes indicates that Dictyostelium diverged from the line leading to mammals about the same time as the plant and animal divergence. Therefore, the comparison of these eight proteins shows evidence that mammals are more closely related to Dictyostelium than to yeast. The experiment that was conducted by Loomis and Smith in 1990 suggested that yeast diverged much earlier.