Archezoa

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In Biology, Archezoa is a term that has been introduced by several authors to refer to a group of organisms (a taxon). Authors include Josef Anton Maximilian Perty, [1] Ernst Haeckel [2] and in the 20th century by Thomas Cavalier-Smith in his classification system. Each author used the name to refer to different arrays of organisms. This reuse by later authors of the same taxon name for different groups of organisms is widely criticized in taxonomy because the inclusion of the name in a sentence (e.g. "Archezoa have no olfactory organs") does not make sense unless the particular usage is specified (e.g. "Archezoa sensu Cavalier-Smith (1987) have no olfactory organs"). Nonetheless, all uses of 'Archezoa' are now obsolete.

Contents

Archezoa sensu Cavalier-Smith (1987)

Cavalier Smith proposed the term 'Archezoa' for a paraphyletic (see Paraphyly) territory of eukaryotes that primitively lacked mitochondria. Like Margulis and others before (see Pelomyxa), Cavalier-Smith argued that the initial ancestor of eukaryotes emerged prior to the endosymbiotic acquisition (see endosymbiosis) of mitochondria. [3] The same paraphyletic territory was referred to as 'Hypochondria' by others. [4] The argument for Archezoa sensu Cavalier-Smith was never universally accepted because of conflicting information, and was dropped when the contrary argument, that amitochondriates were descendants of eukaryotes with mitochondria, became dominant.

Eukaryotes that eventually acquired a bacterial endosymbiont that became the mitochondria were placed in a taxonomic group which Cavalier-Smith called the Metakaryota, whereas the Archezoa represented an earlier paraphyletic group to which Cavalier-Smith variously assigned the diplomonads, Entamoeba, Microsporidia, oxymonads, parabasalids (Parabasalids), pelobionts (see Pelomyxa ), retortamonads, trichomonads, and Trimastix [5] (see Cavalier-Smith's system of classification). With the rejection of 'Archeozoa', the meaning of the term 'Metakaryota' became the same as 'Eukaryota' (see Eukaryote), and Metakaryota became superfluous.

Original mitochondria lost

Eukaryotic protists lacking mitochondria were discovered to have experienced secondary mitochondrial loss, meaning that their ancestors once possessed mitochondria but that these mitochondria had, over time, been transformed, reduced, or lost. In some of these organisms, mitochondria had degraded into simpler double-membrane bound organelles known as mitosomes and hydrogenosomes. Some of both types of organelles are known to have fully lost their genome. [6] [7]

Initial discoveries found that amitochondriate organisms appeared to express mitochondrial Hsp60 and Hsp70 proteins from the nuclear DNA of the organism. This indicated that the ancestors of these organisms once possessed mitochondria which expressed these proteins, but that these genes had migrated to their nuclear DNA over time as a result of endosymbiotic gene transfer. [8] [9]

As a result, the argument that some extant eukaryotes lacking mitochondria had emerged from the eukaryotic lineage before mitochondria were acquired was falsified. [10]

Long branch attraction

An argument for the Archezoa group was that amitochondriate protists appeared to branch off early on from the eukaryotic lineage in phylogenetic analyses. This corroborated the supposition that Archezoa were more closely linked to primitive eukaryotes that evolved prior to the endosymbiotic process that generated the mitochondria. [3] However, this early divergence later turned out to be a class of systematic errors in phylogenetic analysis called "long branch attraction". [11] [12]

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<span class="mw-page-title-main">Kingdom (biology)</span> Taxonomic rank

In biology, a kingdom is the second highest taxonomic rank, just below domain. Kingdoms are divided into smaller groups called phyla.

<span class="mw-page-title-main">Symbiogenesis</span> Evolutionary theory holding that eukaryotic organelles evolved through symbiosis with prokaryotes

Symbiogenesis is the leading evolutionary theory of the origin of eukaryotic cells from prokaryotic organisms. The theory holds that mitochondria, plastids such as chloroplasts, and possibly other organelles of eukaryotic cells are descended from formerly free-living prokaryotes taken one inside the other in endosymbiosis. Mitochondria appear to be phylogenetically related to Rickettsiales bacteria, while chloroplasts are thought to be related to cyanobacteria.

<span class="mw-page-title-main">Excavata</span> Supergroup of unicellular organisms belonging to the domain Eukaryota

Excavata is an extensive and diverse but paraphyletic group of unicellular Eukaryota. The group was first suggested by Simpson and Patterson in 1999 and the name latinized and assigned a rank by Thomas Cavalier-Smith in 2002. It contains a variety of free-living and symbiotic protists, and includes some important parasites of humans such as Giardia and Trichomonas. Excavates were formerly considered to be included in the now obsolete Protista kingdom. They were distinguished from other lineages based on electron-microscopic information about how the cells are arranged. They are considered to be a basal flagellate lineage.

<span class="mw-page-title-main">Thomas Cavalier-Smith</span> British evolutionary biologist (1942–2021)

Thomas (Tom) Cavalier-Smith, FRS, FRSC, NERC Professorial Fellow, was a professor of evolutionary biology in the Department of Zoology, at the University of Oxford.

<span class="mw-page-title-main">Amoebozoa</span> Phylum of protozoans

Amoebozoa is a major taxonomic group containing about 2,400 described species of amoeboid protists, often possessing blunt, fingerlike, lobose pseudopods and tubular mitochondrial cristae. In traditional classification schemes, Amoebozoa is usually ranked as a phylum within either the kingdom Protista or the kingdom Protozoa. In the classification favored by the International Society of Protistologists, it is retained as an unranked "supergroup" within Eukaryota. Molecular genetic analysis supports Amoebozoa as a monophyletic clade. Modern studies of eukaryotic phylogenetic trees identify it as the sister group to Opisthokonta, another major clade which contains both fungi and animals as well as several other clades comprising some 300 species of unicellular eukaryotes. Amoebozoa and Opisthokonta are sometimes grouped together in a high-level taxon, variously named Unikonta, Amorphea or Opimoda.

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<span class="mw-page-title-main">Metamonad</span> Phylum of excavate protists

The metamonads are a large group of flagellate amitochondriate microscopic eukaryotes. Their composition is not entirely settled, but they include the retortamonads, diplomonads, and possibly the parabasalids and oxymonads as well. These four groups are all anaerobic, occurring mostly as symbiotes or parasites of animals, as is the case with Giardia lamblia which causes diarrhea in mammals.

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<span class="mw-page-title-main">Lobosa</span> Phylum of protozoans

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<span class="mw-page-title-main">Apusozoa</span> Phylum of micro-organisms

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<span class="mw-page-title-main">Archamoebae</span> Phylum of protists

The Archamoebae are a group of protists originally thought to have evolved before the acquisition of mitochondria by eukaryotes. They include genera that are internal parasites or commensals of animals. A few species are human pathogens, causing diseases such as amoebic dysentery. The other genera of archamoebae live in freshwater habitats and are unusual among amoebae in possessing flagella. Most have a single nucleus and flagellum, but the giant amoeba Pelomyxa has many of each.

<i>Breviata</i> Genus of flagellated amoebae

Breviata anathema is a single-celled flagellate amoeboid eukaryote, previously studied under the name Mastigamoeba invertens. The cell lacks mitochondria, much like the pelobionts to which the species was previously assigned, but has remnant mitochondrial genes, and possesses an organelle believed to be a modified anaerobic mitochondrion, similar to the mitosomes and hydrogenosomes found in other eukaryotes that live in low-oxygen environments.

<span class="mw-page-title-main">Conosa</span> Phylum of protozoans

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<i>Mastigamoeba</i> Genus of flagellar amoeboids

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<span class="mw-page-title-main">Eukaryote</span> Domain of life whose cells have nuclei

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<span class="mw-page-title-main">Breviatea</span> Group of protists

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References

  1. ↑ Perty, M. 1852. Zur Kenntnis kleinster Lebensformen nach Bau, Funktionen, Systematik, mit Spezialverzeichniss der in der Schweiz beobachteten. Jent & Reinert, Bern
  2. ↑ Haeckel, E. 1866. Generelle Morphologie der Organismen Vols I and II. Reimer.
  3. 1 2 Cavalier-Smith, T. (1987). "Eukaryotes with no mitochondria". Nature. 326 (6111): 332–333. Bibcode:1987Natur.326..332C. doi:10.1038/326332a0. ISSN   1476-4687. PMID   3561476. S2CID   4351363.
  4. ↑ Embley, T. M. (2006). "Multiple secondary origins of the anaerobic lifestyle in eukaryotes". Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences. 361 (1470): 1055–1067. doi:10.1098/rstb.2006.1844. PMC   1578728 . PMID   16754614.
  5. ↑ Gray, Michael W.; Burger, Gertraud; Lang, B. Franz (1999-03-05). "Mitochondrial evolution". Science. 283 (5407): 1476–1481. Bibcode:1999Sci...283.1476G. doi:10.1126/science.283.5407.1476. ISSN   0036-8075. PMC   3428767 . PMID   10066161.
  6. ↑ Embley, T. Martin; Hirt, Robert P. (1998). "Early branching eukaryotes?". Current Opinion in Genetics & Development. 8 (6): 624–629. doi:10.1016/S0959-437X(98)80029-4. PMID   9914207.
  7. ↑ Roger, Andrew J. (1999). "Reconstructing early events in eukaryotic evolution". The American Naturalist. 154 (S4): S146–S163. doi:10.1086/303290. ISSN   0003-0147. PMID   10527924. S2CID   32138852.
  8. ↑ Clark, C.G.; Roger, A.J. (1995). "Direct evidence for secondary loss of mitochondria in Entamoeba histolytica". Proc. Natl. Acad. Sci. USA. 92 (14): 6518–6521. Bibcode:1995PNAS...92.6518C. doi: 10.1073/pnas.92.14.6518 . PMC   41549 . PMID   7604025.
  9. ↑ Roger, A.J. (1999). "Reconstructing early events in eukaryotic evolution". Am. Nat. 154 (S4): S146–S163. doi:10.1086/303290. PMID   10527924. S2CID   32138852.
  10. ↑ Embley, T.M.; Martin, W. (2006). "Eukaryotic evolution, changes and challenges". Nature. 440 (7084): 623–630. Bibcode:2006Natur.440..623E. doi:10.1038/nature04546. PMID   16572163. S2CID   4396543.
  11. ↑ Brinkmann, Henner; Philippe, Hervé (2007). "The Diversity of Eukaryotes and the Root of the Eukaryotic Tree". Eukaryotic Membranes and Cytoskeleton. Advances in Experimental Medicine and Biology. Vol. 607. New York, NY: Springer New York. pp. 20–37. doi:10.1007/978-0-387-74021-8_2. ISBN   978-0-387-74020-1. PMID   17977456 . Retrieved 2022-02-01.
  12. ↑ Gray, M.W. (2012-09-01). "Mitochondrial evolution". Cold Spring Harbor Perspectives in Biology. 4 (9): a011403. doi:10.1101/cshperspect.a011403. ISSN   1943-0264. PMC   3428767 . PMID   22952398.
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