An expanded phylogeny of social amoebas (Dictyostelia) shows increasing diversity and new morphological patterns

Abstract

BackgroundSocial Amoebae or Dictyostelia are eukaryotic microbes with a unique life cycle consisting of both uni- and multicellular stages. They have long fascinated molecular, developmental and evolutionary biologists, and Dictyostelium discoideum is now one of the most widely studied eukaryotic microbial models. The first molecular phylogeny of Dictyostelia included most of the species known at the time and suggested an extremely deep taxon with a molecular depth roughly equivalent to Metazoa. The group was also shown to consist of four major clades, none of which correspond to traditional genera. Potential morphological justification was identified for three of the four major groups, on the basis of which tentative names were assigned.ResultsOver the past four years, the Mycetozoan Global Biodiversity Survey has identified many new isolates that appear to be new species of Dictyostelia, along with numerous isolates of previously described species. We have determined 18S ribosomal RNA gene sequences for all of these new isolates. Phylogenetic analyses of these data show at least 50 new species, and these arise from throughout the dictyostelid tree breaking up many previously isolated long branches. The resulting tree now shows eight well-supported major groups instead of the original four. The new species also expand the known morphological diversity of the previously established four major groups, violating nearly all previously suggested deep morphological patterns.ConclusionsA greatly expanded phylogeny of Dictyostelia now shows even greater morphological plasticity at deep taxonomic levels. In fact, there now seem to be no obvious deep evolutionary trends across the group. However at a finer level, patterns in morphological character evolution are beginning to emerge. These results also suggest that there is a far greater diversity of Dictyostelia yet to be discovered, including novel morphologies.

Novel Diversity of Deeply Branching Holomycota and Unicellular Holozoans Revealed by Metabarcoding in Middle Paraná River, Argentina

“…This is also in agreement with previous studies that found a large undetected diversity within this lineage, and highlights the importance of unraveling it to understand its evolution (Romeralo et al, 2011;Fiz-Palacios et al, 2013;Tekle et al, 2016;Kang et al, 2017).…”

A core phylogeny of Dictyostelia inferred from genomes representative of the eight major and minor taxonomic divisions of the group

“…Just like groups 1 and 2 in branch I, which are sister clades that evolved independently, groups 3 and 4 are sister clades in branch II, but with Pvio, one of six taxa in the "violaceum" complex [12] occupying a basal position to group 4. Group 4 taxa display major phenotypic innovations, such as two more cell types, cell-type proportioning, extensive slug migration and enhanced fruiting body robustness, which are not yet evident in the “violaceum” complex [18, 20].…”

“…The latter was improved by sequencing of the less conserved internal transcribed spacer (ITS) regions between the ribosomal RNAs [11]. Further expansion of the phylogeny with 47 new taxa indicated that the intermediate species may actually represent additional minor groups, which were named the violaceum, polycephalum and polycarpum complexes [12]. …”

An ancestral bacterial division system is widespread in eukaryotic mitochondria

“…Here, D. discoideum, Dictyostelium citrinum, Dictyostelium intermedium, and Dictyostelium firmibasis have retained only FtsZ whereas their sister taxon D. purpureum and the more basal taxa P. pallidum, Polysphondylium violaceum, and A. subglobosum have additionally maintained all three Min proteins. Meanwhile, the yet more distantly related Dictyostelium fasciculatum (72,73) seems to have independently lost the Min proteins and, like D. discoideum, only possesses FtsZ. This overall pattern raises the question of why Min proteins were retained in some taxa, yet lost in others.…”