Domains (biology)


August 13, 2022

Domain (dominium) - a systematic category higher than kingdom, used in biological classification, proposed in 1974 by Royall T. Moore, and introduced in 1990 by Carl Woese, Otto Kandler and Mark Wheelis as the highest level category (with the highest rank taxonomic). A domain is a category equivalent to the names later proposed by other taxonomists: empire (empire) or super kingdom (superregnum).

Authors rationale

Mycologist Royall T. Moore proposed in 1974 the introduction of additional "super" categories, including domains, with the Latin equivalent of the Dominion. The domain would be the highest systematic category encompassing, as immediately subordinate categories, the existing kingdoms. In 1990, Woese and others stated that the systematic division of organisms into five kingdoms to date did not reflect the state of the art at the time. On the basis of molecular studies, they decided that life on Earth should be systematized into three groups, which they gave the domain rank proposed by Moore (but with the Latin equivalent of regio) and named it: Bacteria, Archaea and Eucarya. The domains they proposed included the existing and new kingdoms, which - in their opinion - should still be described. The introduction of a new category of higher rank was intended to avoid destroying the traditionally established division into kingdoms. In the work of 1990 the authors did not define kingdoms for Bacteria and Eucarya, limiting themselves only to saying that there will be many of them, and their definition requires further analysis. However, for the Archaea domain, they proposed a division into Euryarchaeota and Crenarchaeota.

Division of organisms into three domains

bacteria (Bacteria) - apart from the actual bacteria, it includes cyanobacteria and prochlorophytes archaea (Archaea) - includes prokaryotic organisms with a structure distinctly different from bacteria eukaryotes (Eucarya) - includes about 60 independent lines of development temporarily grouped into four kingdoms: protists (Protista) mushrooms (Fungi) plants (Plantae) animals (Animalia) This division was made by merely comparing the rRNA sequences, but then numerous facts were found to match it. From the point of view of the biochemistry and physiology of cells, archaea are very different from the proper bacteria, some features bring them closer to the nucleoli.

Alternate splits

There is also an alternative split into two empires (Prokaryota [Bacteria] and Eukaryota) with six kingdoms, proposed by Thomas Cavalier-Smith in 2004. empire: bacteria (Bacteria) - in the original version of the Prokaryote with the kingdom of Bacteria: eubacteria (Eubacteria) archaea (Archaea) empire: eukaryotes (Eukaryotes): Archezoa - primitive eukaryotes without chloroplasts and mitochondria Protozoa - unicellular cells without cell walls, but with mitochondria chromisty (Chromista) - mainly algae and some fungi plants (Plantae) - including green algae mushrooms (Fungi) animals (Animalia), but it is not very popular, mainly due to the lack of certainty as to the relationships between groups of eukaryotes. The American systematist Lynn Margulis is of the opinion that the separation of prokaryotes into two high-ranking taxa is not sufficiently justified, because despite significant biochemical differences, they are much more similar to each other than to nuclear organisms. This is due to the recognition of the cell structure as a more important systematic feature than biochemical features - especially since biochemical features can be "exchanged" between even distantly related organisms through horizontal gene transfer.