The cellular slime mold Dictyostelium has cell-cell connections similar in structure, function, and underlying molecular mechanisms to animal epithelial cells. These similarities form the basis for the proposal that multicellularity is ancestral to the clade containing animals, fungi, and Amoebozoa (including Dictyostelium): Amorphea (formerly “unikonts”). This hypothesis is intriguing and if true could precipitate a paradigm shift. However, phylogenetic analyses of two key genes reveal patterns inconsistent with a single origin of multicellularity. A single origin in Amorphea would also require loss of multicellularity in each of the many unicellular lineages within this clade. Further, there are numerous other origins of multicellularity within eukaryotes, including three within Amorphea, that are not characterized by these structural and mechanistic similarities. Instead, convergent evolution resulting from similar selective pressures for forming multicellular structures with motile and differentiated cells is the most likely explanation for the observed similarities between animal and dictyostelid cell-cell connections.
All major clades of eukaryotes harbor multicellular taxa that evolved from unicellular ancestors. Similarities in the nature of multicellular cell-cell connections between animals and the slime mold Dictyostelium arose through convergence at the molecular and morphological level, not from common ancestry as was recently proposed. Image credits: David Patterson (starcentral.mbl.edu/microscope) and Alvaro Migotto (cifonauta.cebimar.usp.br).