User:Kira-g.w.w./Social Amoeba Evolution

The amoebozoans are a genetically diverse protist group that is the closest sister group to the clade containing the animals and fungi. One group of amoebae are the cellular slime molds, referred to as social amoebae. Social amoebae are common microorganismal inhabitants of the soil and play a role in maintaining the natural balance between bacteria and other microorganisms in the soil environment. Four major groups are distinguished by DNA-constructed phylogenies for all known species of the social amoebae. Evolutionary trends are mapped based on the morphologies and phenotypes of the fruiting bodies such as: fruiting body size, spore size, spore shape, coloration, and branching patterns.

= The Evolution of Social Amoeba =

Background
[[File:SALC.jpg|thumb|The life cycle of social amoeba.

DiSalvo Lab Home 2021 ]] Protists are ubiquitous in nature: They can be found in both terrestrial and aquatic biomes. Terrestrial, soil-dwelling protists - particularly amoeba - are a common inhabitant of the soil and play a role in primary production by contributing to decomposition, mineralization, and they also have a role in nutrient cycling, transferring nutrients to higher order consumers in the soil food web. The soil microbiome is a diverse ecosystem with a broad and variable array of soil microorganisms.

One group of amoebae are the social amoebae (Dictyostelia), also referred to as cellular slime molds, are known for their life cycle. While they exist primarily as solitary unicellular organisms feeding on bacteria, when their food source becomes depleted, the dictystelids have evolved specific cellular responses. Dictyostelids form microcysts for their vegetative state, or encystment; this formation evolved from early amoebazoans. They can form macrocysts for their sexual stage; however, this is not observed in recent dictyostelid species. More so, thousands of cells will aggregate to form a temporary multicellular organism (fruiting body). The goal of this formation is to reach the soil surface and form a fruiting body containing spores. These spores can then be dispersed to a more food-rich environment and at that point they then revert to their unicellular stage. This aggregative development has evolved in multiple lineages of eukaryotes. Dictyostelids are now used as model organisms to studying a variety of biological questions world-wide due to their ease of cultivation in the lab, production of fruiting bodies that are identifiable by morphologies, and their ability to feed on a wide range of bacterial cells. Considering that the social amoebae prey upon bacteria, amoeba growth is directional proportional to the growth of bacterial populations.

Discovery
The earliest description of social amoebae was in the mid 1800's by mycologist, Oskar Brefeld. Once considered to be in a the group within Fungi because of the similarities of their sporocarps/fruiting bodies, more recent molecular -based phylogeny has placed these organisms away from fungi and within the protist supergroup Amoebazoa because of their lack of hyphae. These dictyostelids were then placed within the group of acrasids, another phylum of protists. The dictyostelids are now known to differ from the acrasids by the way the amoeboid cells transition during aggregation, this is also confirmed by molecular-based phylogeny. The dictyostelid phylogenetic placements were done so by mycologists; Due to this, the naming system is based on the International Code of Botanical Nomenclature (ICBN). By the late 1950's a total of nine species of social amoebae were known.

Evolution of Social Amoeba Diversity
In the past, the classification of dictyostelids had been identified by their morphological characteristics. These characteristics can included fruiting body size, sorocarps, spore size, spore shape, spore coloration, and branching patterns. By using these morphological identifiers, it was at first noted that there were three genera: Actyostelium, Dictyostelium, and Polysphondylium. Refined cladistic analysis has shown that differentiating the dictyostelids by applying morphology -based taxonomy does not reflect the phylogenetic relationship. Instead, eight clades were then identified and used to distinguish phylogeny. These clades are confirmed by a -tubulin phylogeny and were referenced by a number: Group 1, Group 2A, Group 2B, Group 3, Group4, plus the complexes "polycarpum", "polycephalum", and "violaceum" .

Currently, molecular analyses are used to determine the classification system of amoebozoans. This is based on phylogenetic analysis of small subunit rRNA (SSU rRNA) gene sequences.

Presently, there are two major clades in the phylogeny ranked as an order. The two orders are the Acytosteliales and the Dictyosteliales. Further, two clades within each order are given the rank of family: Acytosteliaceae and Cavenderiaceae in the order Acytosteliales, and Dictyosteliaceae and Raperosteliaceae in the order Dictyosteliales.

Additionally, twelve taxa are recognized at the genus level and correspond to the previously referenced groupings. Cavenderia corresponds with Group 1, Acytostelium corresponds with Group 2A, Rostrostelium corresponds with only Acytostelium ellopticum in Group 2B, Heterostelium corresponds with the remaining members in Group 2B except A. ellipticum, Speleostelium including only Ditcyostelium caveatum ''. Tieghemostelium, Hagiwaraea, and Raperostelium correspond to members within Group 3, Dictyostelium corresponds with Group 4, Coremiostelium corresponding with the "polycephalum" complex, Polysphondylium corresponding with the "violaceum" complex, and Synstelium corresponding with the "polycarpum"'' complex.

Diagnostic features for each family, within their respective order are described below.

Acytosteliales

 * Cavenderiaceae

Sorocarps with cellular stalks, solitary to loosely or (rarely) tightly clustered, unbranched or irregularly branched, white-hyaline or pale yellow. Spores oblong to elliptic or reniform in outline, with consolidated polar or subpolar granules.


 * Acytosteliaceae

Sorocarps with cellular or acellular stalks, colorless or white hyaline, solitary or loosely to tightly clustered, branching absent or usually sparse where it occurs, sometimes in regularly spaced whorls, the sorogens sometimes ventricose-rostrate. Spores globose to irregularly rounded or ellipsoid, granules present or absent.

Dictyosteliales

 * Raperosteliaceae

Sorocarps with cellular stalks, sometimes with acellular apical stretches, colorless, solitary or clustered, sometimes with cramponshaped bases, unbranched or with irregularly spaced branches. Spores ellipsoid to globose or oblong, granules present or absent.


 * Dictyosteliaceae

Sorocarps with cellular stalks, sometimes with acellular apical stretches, sometimes with crampon-like bases, colorless or with white to pale yellow or purple sori. Habit solitary, clustered or coremiform. Branches absent, irregular or in regularly spaced whorls. Spores elliptic or oblong in outline, granules present or absent.

Influences on Diversity
Due to the fact that social amoebae are soil -dwelling microorganisms, environmental factors that may influence amoebae diversity include, but are not limited to, temperature, light -exposure, soil moisture, humidity, pH, air circulation, and other microorganisms in their niche (bacterial symbionts). These ecological factors could influence the diversity either singularly or used in conjunction with one another.