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'''Excavata''' is an extensive and diverse but possibly [[paraphyletic]] group of unicellular [[Eukaryota]].<ref name="pmid19237557">{{cite journal | vauthors = Hampl V, Hug L, Leigh JW, Dacks JB, Lang BF, Simpson AG, Roger AJ | title = Phylogenomic analyses support the monophyly of Excavata and resolve relationships among eukaryotic "supergroups" | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 106 | issue = 10 | pages = 3859–3864 | date = March 2009 | pmid = 19237557 | pmc = 2656170 | doi = 10.1073/pnas.0807880106 | doi-access = free | bibcode = 2009PNAS..106.3859H }}</ref><ref name=simpson>{{cite journal | vauthors = Simpson AG, Inagaki Y, Roger AJ | title = Comprehensive multigene phylogenies of excavate protists reveal the evolutionary positions of "primitive" eukaryotes | journal = Molecular Biology and Evolution | volume = 23 | issue = 3 | pages = 615–625 | date = March 2006 | pmid = 16308337 | doi = 10.1093/molbev/msj068 | doi-access = free }}</ref> The group was first suggested by Simpson and Patterson in 1999<ref name="Simpson1999">{{Cite journal | vauthors = Simpson AG, Patterson DJ |date=December 1999 |title=The ultrastructure of Carpediemonas membranifera (Eukaryota) with reference to the 'excavate hypothesis' |journal=European Journal of Protistology |volume=35 |issue=4 |pages=353–370 |doi=10.1016/S0932-4739(99)80044-3}}</ref><ref name="Simpson2003">{{cite journal | vauthors = Simpson AG | title = Cytoskeletal organization, phylogenetic affinities and systematics in the contentious taxon Excavata (Eukaryota) | journal = International Journal of Systematic and Evolutionary Microbiology | volume = 53 | issue = Pt 6 | pages = 1759–1777 | date = November 2003 | pmid = 14657103 | doi = 10.1099/ijs.0.02578-0 | doi-access = free }}</ref> 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]]''.<ref name="Ancestor">{{cite book |title=The Ancestor's Tale |isbn=978-0-544-85993-7 | vauthors = Dawkins R, Wong Y |author1-link=Richard Dawkins |year=2016 |title-link=The Ancestor's Tale | location = Boston | publisher = Houghton Mifflin Harcourt }}</ref> Excavates were formerly considered to be included in the now obsolete [[Protists|Protista]] kingdom.<ref name="pmid11931142">{{cite journal | vauthors = Cavalier-Smith T | title = The phagotrophic origin of eukaryotes and phylogenetic classification of Protozoa | journal = International Journal of Systematic and Evolutionary Microbiology | volume = 52 | issue = Pt 2 | pages = 297–354 | date = March 2002 | pmid = 11931142 | doi = 10.1099/00207713-52-2-297 }}</ref> They were distinguished from other lineages based on electron-microscopic information about how the cells are arranged (they have a distinctive [[ultrastructural identity]]).<ref name="Simpson2003" /> They are considered to be a basal [[flagellate]] lineage.<ref>{{cite journal | vauthors = Dawson SC, Paredez AR | title = Alternative cytoskeletal landscapes: cytoskeletal novelty and evolution in basal excavate protists | journal = Current Opinion in Cell Biology | volume = 25 | issue = 1 | pages = 134–141 | date = February 2013 | pmid = 23312067 | pmc = 4927265 | doi = 10.1016/j.ceb.2012.11.005 }}</ref>
'''Excavata''' is an extensive and diverse but possibly [[paraphyletic]] group of unicellular [[Eukaryota]].<ref name="pmid19237557">{{cite journal | vauthors = Hampl V, Hug L, Leigh JW, Dacks JB, Lang BF, Simpson AG, Roger AJ | title = Phylogenomic analyses support the monophyly of Excavata and resolve relationships among eukaryotic "supergroups" | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 106 | issue = 10 | pages = 3859–3864 | date = March 2009 | pmid = 19237557 | pmc = 2656170 | doi = 10.1073/pnas.0807880106 | doi-access = free | bibcode = 2009PNAS..106.3859H }}</ref><ref name=simpson>{{cite journal | vauthors = Simpson AG, Inagaki Y, Roger AJ | title = Comprehensive multigene phylogenies of excavate protists reveal the evolutionary positions of "primitive" eukaryotes | journal = Molecular Biology and Evolution | volume = 23 | issue = 3 | pages = 615–625 | date = March 2006 | pmid = 16308337 | doi = 10.1093/molbev/msj068 | doi-access = free }}</ref> The group was first suggested by Simpson and Patterson in 1999<ref name="Simpson1999">{{Cite journal | vauthors = Simpson AG, Patterson DJ |date=December 1999 |title=The ultrastructure of Carpediemonas membranifera (Eukaryota) with reference to the 'excavate hypothesis' |journal=European Journal of Protistology |volume=35 |issue=4 |pages=353–370 |doi=10.1016/S0932-4739(99)80044-3}}</ref><ref name="Simpson2003">{{cite journal | vauthors = Simpson AG | title = Cytoskeletal organization, phylogenetic affinities and systematics in the contentious taxon Excavata (Eukaryota) | journal = International Journal of Systematic and Evolutionary Microbiology | volume = 53 | issue = Pt 6 | pages = 1759–1777 | date = November 2003 | pmid = 14657103 | doi = 10.1099/ijs.0.02578-0 | doi-access = free }}</ref> 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]]''.<ref name="Ancestor">{{cite book |title=The Ancestor's Tale |isbn=978-0-544-85993-7 | vauthors = Dawkins R, Wong Y |author1-link=Richard Dawkins |year=2016 |title-link=The Ancestor's Tale | location = Boston | publisher = Houghton Mifflin Harcourt }}</ref> Excavates were formerly considered to be included in the now obsolete [[Protists|Protista]] kingdom.<ref name="pmid11931142">{{cite journal | vauthors = Cavalier-Smith T | title = The phagotrophic origin of eukaryotes and phylogenetic classification of Protozoa | journal = International Journal of Systematic and Evolutionary Microbiology | volume = 52 | issue = Pt 2 | pages = 297–354 | date = March 2002 | pmid = 11931142 | doi = 10.1099/00207713-52-2-297 }}</ref> They were distinguished from other lineages based on electron-microscopic information about how the cells are arranged (they have a distinctive [[ultrastructural identity]]).<ref name="Simpson2003" /> They are considered to be a basal [[flagellate]] lineage.<ref>{{cite journal | vauthors = Dawson SC, Paredez AR | title = Alternative cytoskeletal landscapes: cytoskeletal novelty and evolution in basal excavate protists | journal = Current Opinion in Cell Biology | volume = 25 | issue = 1 | pages = 134–141 | date = February 2013 | pmid = 23312067 | pmc = 4927265 | doi = 10.1016/j.ceb.2012.11.005 }}</ref>


On the basis of phylogenomic analyses, the group was shown to contain three monophyletic groups (discobids, metamonads, and malawimonads), the relationships among which and indeed their monophyly are uncertain.<ref name="pmid31606140">{{cite journal | vauthors = Burki F, Roger AJ, Brown MW, Simpson AG | title = The New Tree of Eukaryotes | journal = Trends in Ecology & Evolution | volume = 35 | issue = 1 | pages = 43–55 | date = January 2020 | pmid = 31606140 | doi = 10.1016/j.tree.2019.08.008 }}</ref><ref>{{cite journal | vauthors = Brown MW, Heiss AA, Kamikawa R, Inagaki Y, Yabuki A, Tice AK, Shiratori T, Ishida KI, Hashimoto T, Simpson AG, Roger AJ | display-authors = 6 | title = Phylogenomics Places Orphan Protistan Lineages in a Novel Eukaryotic Super-Group | journal = Genome Biology and Evolution | volume = 10 | issue = 2 | pages = 427–433 | date = February 2018 | pmid = 29360967 | pmc = 5793813 | doi = 10.1093/gbe/evy014 }}</ref><ref>{{cite journal | vauthors = Heiss AA, Kolisko M, Ekelund F, Brown MW, Roger AJ, Simpson AG | title = Combined morphological and phylogenomic re-examination of malawimonads, a critical taxon for inferring the evolutionary history of eukaryotes | journal = Royal Society Open Science | volume = 5 | issue = 4 | pages = 171707 | date = April 2018 | pmid = 29765641 | pmc = 5936906 | doi = 10.1098/rsos.171707 | bibcode = 2018RSOS....571707H }}</ref><ref>{{cite journal | vauthors = Keeling PJ, Burki F | title = Progress towards the Tree of Eukaryotes | journal = Current Biology | volume = 29 | issue = 16 | pages = R808-R817 | date = August 2019 | pmid = 31430481 | doi = 10.1016/j.cub.2019.07.031 | doi-access = free }}</ref> A current view of the composition of the excavates is given below, indicating that the group is paraphyletic. Except for some [[Euglenozoa]], all are non-photosynthetic.
On the basis of phylogenomic analyses, the group was shown to contain three monophyletic groups (discobids, metamonads, and malawimonads), the relationships among which and indeed their monophyly are uncertain.<ref name="pmid31606140">{{cite journal | vauthors = Burki F, Roger AJ, Brown MW, Simpson AG | title = The New Tree of Eukaryotes | journal = Trends in Ecology & Evolution | volume = 35 | issue = 1 | pages = 43–55 | date = January 2020 | pmid = 31606140 | doi = 10.1016/j.tree.2019.08.008 | s2cid = 204545629 }}</ref><ref>{{cite journal | vauthors = Brown MW, Heiss AA, Kamikawa R, Inagaki Y, Yabuki A, Tice AK, Shiratori T, Ishida KI, Hashimoto T, Simpson AG, Roger AJ | display-authors = 6 | title = Phylogenomics Places Orphan Protistan Lineages in a Novel Eukaryotic Super-Group | journal = Genome Biology and Evolution | volume = 10 | issue = 2 | pages = 427–433 | date = February 2018 | pmid = 29360967 | pmc = 5793813 | doi = 10.1093/gbe/evy014 }}</ref><ref>{{cite journal | vauthors = Heiss AA, Kolisko M, Ekelund F, Brown MW, Roger AJ, Simpson AG | title = Combined morphological and phylogenomic re-examination of malawimonads, a critical taxon for inferring the evolutionary history of eukaryotes | journal = Royal Society Open Science | volume = 5 | issue = 4 | pages = 171707 | date = April 2018 | pmid = 29765641 | pmc = 5936906 | doi = 10.1098/rsos.171707 | bibcode = 2018RSOS....571707H }}</ref><ref>{{cite journal | vauthors = Keeling PJ, Burki F | title = Progress towards the Tree of Eukaryotes | journal = Current Biology | volume = 29 | issue = 16 | pages = R808–R817 | date = August 2019 | pmid = 31430481 | doi = 10.1016/j.cub.2019.07.031 | doi-access = free }}</ref> A current view of the composition of the excavates is given below, indicating that the group is paraphyletic. Except for some [[Euglenozoa]], all are non-photosynthetic.


==Characteristics==
==Characteristics==
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{{anchor|Discoba}}
{{anchor|Discoba}}


Excavate relationships were always uncertain, suggesting that they are not a [[monophyletic]] group.<ref name="pmid17194223">{{cite journal | vauthors = Parfrey LW, Barbero E, Lasser E, Dunthorn M, Bhattacharya D, Patterson DJ, Katz LA | author-link1 = Laura Wegener Parfrey | title = Evaluating support for the current classification of eukaryotic diversity | journal = PLoS Genetics | volume = 2 | issue = 12 | pages = e220 | date = December 2006 | pmid = 17194223 | pmc = 1713255 | doi = 10.1371/journal.pgen.0020220 | url = }}</ref> The malawimonads often do not branch with the other Excavata.<ref>{{cite journal | vauthors = Tice AK, Žihala D, Pánek T, Jones RE, Salomaki ED, Nenarokov S, Burki F, Eliáš M, Eme L, Roger AJ, Rokas A, Shen XX, Strassert JF, Kolísko M, Brown MW | display-authors = 6 | title = PhyloFisher: A phylogenomic package for resolving eukaryotic relationships | journal = PLoS Biology | volume = 19 | issue = 8 | pages = e3001365 | date = August 2021 | pmid = 34358228 | pmc = 8345874 | doi = 10.1371/journal.pbio.3001365 }}</ref>
Excavate relationships were always uncertain, suggesting that they are not a [[monophyletic]] group.<ref name="pmid17194223">{{cite journal | vauthors = Parfrey LW, Barbero E, Lasser E, Dunthorn M, Bhattacharya D, Patterson DJ, Katz LA | author-link1 = Laura Wegener Parfrey | title = Evaluating support for the current classification of eukaryotic diversity | journal = PLOS Genetics | volume = 2 | issue = 12 | pages = e220 | date = December 2006 | pmid = 17194223 | pmc = 1713255 | doi = 10.1371/journal.pgen.0020220 | url = | doi-access = free }}</ref> The malawimonads often do not branch with the other Excavata.<ref>{{cite journal | vauthors = Tice AK, Žihala D, Pánek T, Jones RE, Salomaki ED, Nenarokov S, Burki F, Eliáš M, Eme L, Roger AJ, Rokas A, Shen XX, Strassert JF, Kolísko M, Brown MW | display-authors = 6 | title = PhyloFisher: A phylogenomic package for resolving eukaryotic relationships | journal = PLOS Biology | volume = 19 | issue = 8 | pages = e3001365 | date = August 2021 | pmid = 34358228 | pmc = 8345874 | doi = 10.1371/journal.pbio.3001365 | doi-access = free }}</ref>


Excavates were thought to include multiple groups:
Excavates were thought to include multiple groups:
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===Metamonads===
===Metamonads===


Metamonads are unusual in not having classical mitochondria—instead they have [[hydrogenosome]]s, [[mitosome]]s or uncharacterised organelles. The oxymonad ''[[Monocercomonoides]]'' is reported to have completely lost homologous organelles. There are competing explanations.<ref>{{cite journal | vauthors = Bui ET, Bradley PJ, Johnson PJ | title = A common evolutionary origin for mitochondria and hydrogenosomes | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 93 | issue = 18 | pages = 9651–9656 | date = September 1996 | pmid = 8790385 | pmc = 38483 | doi = 10.1073/pnas.93.18.9651 }}</ref><ref name="Al Jewari Baldauf 2023" />
Metamonads are unusual in not having classical mitochondria—instead they have [[hydrogenosome]]s, [[mitosome]]s or uncharacterised organelles. The oxymonad ''[[Monocercomonoides]]'' is reported to have completely lost homologous organelles. There are competing explanations.<ref>{{cite journal | vauthors = Bui ET, Bradley PJ, Johnson PJ | title = A common evolutionary origin for mitochondria and hydrogenosomes | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 93 | issue = 18 | pages = 9651–9656 | date = September 1996 | pmid = 8790385 | pmc = 38483 | doi = 10.1073/pnas.93.18.9651 | doi-access = free }}</ref><ref name="Al Jewari Baldauf 2023" />


===Malawimonads===
===Malawimonads===
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{{further|Eukaryogenesis}}
{{further|Eukaryogenesis}}


The conventional explanation for the origin of the Eukaryotes is that a [[heimdallarchaeia]]n<ref name="Eme 2023">{{Cite journal | vauthors = Eme L, Tamarit D, Caceres EF, Stairs CW, Anda VD, Schön ME, Seitz KW, Dombrowski N, Lewis WH, Homa F, Saw JH, Lombard J, Nunoura T, Li W, Hua Z | display-authors = 6 |date=2023-03-09 |title=Inference and reconstruction of the heimdallarchaeial ancestry of eukaryotes | journal = bioRxiv |pages=2023.03.07.531504 |doi=10.1101/2023.03.07.531504v1}}</ref> or another Archaea acquired an [[Alphaproteobacteria|alphaproteobacterium]] as an [[Endosymbiont hypothesis|endosymbiont]], and that this became the [[mitochondrion]], the [[organelle]] providing [[Citric acid cycle|oxidative respiration]] to the eukaryotic cell. Caesar al Jewari and Sandra Baldauf argue instead that the Eukaryotes possibly started with an endosymbiosis event of a deltaproteobacterium or gammaproteobacterium, accounting for the otherwise unexplained presence of anaerobic bacterial enzymes in metamonada in this scenario. The sister of the Preaxostyla within Metamonada represents the rest of the Eukaryotes which acquired a alphaproteobacterium.<ref name="Al Jewari Baldauf 2023">{{cite journal | vauthors = Al Jewari C, Baldauf SL | title = An excavate root for the eukaryote tree of life | journal = Science Advances | volume = 9 | issue = 17 | pages = eade4973 | date = April 2023 | pmid = 37115919 | pmc = 10146883 | doi = 10.1126/sciadv.ade4973 }}</ref>
The conventional explanation for the origin of the Eukaryotes is that a [[heimdallarchaeia]]n<ref name="Eme 2023">{{Cite journal | vauthors = Eme L, Tamarit D, Caceres EF, Stairs CW, Anda VD, Schön ME, Seitz KW, Dombrowski N, Lewis WH, Homa F, Saw JH, Lombard J, Nunoura T, Li W, Hua Z | display-authors = 6 |date=2023-03-09 |title=Inference and reconstruction of the heimdallarchaeial ancestry of eukaryotes | journal = bioRxiv | volume = 618 | issue = 7967 |pages=992–999 |doi=10.1101/2023.03.07.531504| pmid = 37316666 | pmc = 10307638 }}</ref> or another Archaea acquired an [[Alphaproteobacteria|alphaproteobacterium]] as an [[Endosymbiont hypothesis|endosymbiont]], and that this became the [[mitochondrion]], the [[organelle]] providing [[Citric acid cycle|oxidative respiration]] to the eukaryotic cell. Caesar al Jewari and Sandra Baldauf argue instead that the Eukaryotes possibly started with an endosymbiosis event of a deltaproteobacterium or gammaproteobacterium, accounting for the otherwise unexplained presence of anaerobic bacterial enzymes in metamonada in this scenario. The sister of the Preaxostyla within Metamonada represents the rest of the Eukaryotes which acquired a alphaproteobacterium.<ref name="Al Jewari Baldauf 2023">{{cite journal | vauthors = Al Jewari C, Baldauf SL | title = An excavate root for the eukaryote tree of life | journal = Science Advances | volume = 9 | issue = 17 | pages = eade4973 | date = April 2023 | pmid = 37115919 | pmc = 10146883 | doi = 10.1126/sciadv.ade4973 }}</ref>


=== Phylogeny ===
=== Phylogeny ===

Revision as of 05:03, 18 September 2023

For an explanation of very similar terms, see Eukaryota.
Excavata
Temporal range: Neoproterozoic–present
Giardia lamblia, a parasitic diplomonad
Scientific classification Edit this classification
(obsolete as paraphyletic)
Domain: Eukaryota
(unranked): Excavata
(Cavalier-Smith), 2002
Phyla and classes

see text

Three types of excavate cells. Top: Jakobida, 1-nucleus, 2-anterior flagellum, 3-ventral/posterior flagellum, 4-ventral feeding groove. Middle: Euglenozoa, 1-nucleus, 2-flagellar pocket/reservoir, 3-dorsal/anterior flagellum, 4-ventral/posterior flagellum, 5-cytostome/feeding apparatus. Bottom: Metamonada, 1-anterior flagella, 2-parabasal body, 3-undulating membrane, 4-posterior flagellum, 5-nucleus, 6-axostyle.

Excavata is an extensive and diverse but possibly paraphyletic group of unicellular Eukaryota.[1][2] The group was first suggested by Simpson and Patterson in 1999[3][4] 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.[5] Excavates were formerly considered to be included in the now obsolete Protista kingdom.[6] They were distinguished from other lineages based on electron-microscopic information about how the cells are arranged (they have a distinctive ultrastructural identity).[4] They are considered to be a basal flagellate lineage.[7]

On the basis of phylogenomic analyses, the group was shown to contain three monophyletic groups (discobids, metamonads, and malawimonads), the relationships among which and indeed their monophyly are uncertain.[8][9][10][11] A current view of the composition of the excavates is given below, indicating that the group is paraphyletic. Except for some Euglenozoa, all are non-photosynthetic.

Characteristics

Most excavates are unicellular, heterotrophic flagellates. Only some Euglenozoa are photosynthetic. In some (particularly anaerobic intestinal parasites), the mitochondria have been greatly reduced.[5] Some excavates lack "classical" mitochondria, and are called "amitochondriate", although most retain a mitochondrial organelle in greatly modified form (e.g. a hydrogenosome or mitosome). Among those with mitochondria, the mitochondrial cristae may be tubular, discoidal, or in some cases, laminar. Most excavates have two, four, or more flagella.[4] Many have a conspicuous ventral feeding groove with a characteristic ultrastructure, supported by microtubules—the "excavated" appearance of this groove giving the organisms their name.[3][6] However, various groups that lack these traits are considered to be derived excavates based on genetic evidence (primarily phylogenetic trees of molecular sequences).[6]

The Acrasidae slime molds are the only excavates to exhibit limited multicellularity. Like other cellular slime molds, they live most of their life as single cells, but will sometimes assemble into larger clusters.

Proposed group

See also: Eukaryote § Phylogeny, and wikispecies:Excavata

Excavate relationships were always uncertain, suggesting that they are not a monophyletic group.[12] The malawimonads often do not branch with the other Excavata.[13]

Excavates were thought to include multiple groups:

Kingdom/Superphylum Included taxa Representative genera (examples) Description
Discoba or JEH or Eozoa Tsukubea Tsukubamonas
Euglenozoa Euglena, Trypanosoma Many important parasites, one large group with plastids (chloroplasts)
Heterolobosea (Percolozoa) Naegleria, Acrasis Most alternate between flagellate and amoeboid forms
Jakobea Jakoba, Reclinomonas Free-living, sometimes loricate flagellates, with very gene-rich mitochondrial genomes
Metamonada or POD Preaxostyla Oxymonads, Trimastix Amitochondriate flagellates, either free-living (Trimastix, Paratrimastix) or living in the hindguts of insects
Fornicata Giardia, Carpediemonas Amitochondriate, mostly symbiotes and parasites of animals.
Parabasalia Trichomonas Amitochondriate flagellates, generally intestinal commensals of insects. Some human pathogens.
Anaeramoeba Anaeramoeba ignava Anaerobic protists with hydrogenosomes instead of mitochondria.
Neolouka Malawimonadida Malawimonas

Discoba or JEH clade

Euglenozoa and Heterolobosea (Percolozoa) or Eozoa (Cavalier-Smith) appear to be particularly close relatives, and are united by the presence of discoid cristae within the mitochondria (Superphylum Discicristata). A close relationship has been shown between Discicristata and Jakobida,[14] the latter having tubular cristae like most other protists, and hence were united under the taxon name Discoba, which was proposed for this apparently monophyletic group.[1]

Metamonads

Metamonads are unusual in not having classical mitochondria—instead they have hydrogenosomes, mitosomes or uncharacterised organelles. The oxymonad Monocercomonoides is reported to have completely lost homologous organelles. There are competing explanations.[15][16]

Malawimonads

The malawimonads have been proposed to be members of Excavata owing to their typical excavate morphology, and phylogenetic affinity to other excavate groups in some molecular phylogenies. However, their position among eukaryotes remains elusive.[2]

Ancyromonads

Ancyromonads are small free-living cells with a narrow longitudinal groove down one side of the cell. The ancyromonad groove is not used for "suspension feeding", unlike in "typical excavates" (e.g. malawimonads, jakobids, Trimastix, Carpediemonas, Kiperferlia, etc). Ancyromonads instead capture prokaryotes attached to surfaces. The phylogenetic placement of ancyromonads is poorly understood (in 2020), however some phylogenetic analyses place them as close relatives of malawimonads.[17]

Evolution

Origin of the Eukaryotes

Further information: Eukaryogenesis

The conventional explanation for the origin of the Eukaryotes is that a heimdallarchaeian[18] or another Archaea acquired an alphaproteobacterium as an endosymbiont, and that this became the mitochondrion, the organelle providing oxidative respiration to the eukaryotic cell. Caesar al Jewari and Sandra Baldauf argue instead that the Eukaryotes possibly started with an endosymbiosis event of a deltaproteobacterium or gammaproteobacterium, accounting for the otherwise unexplained presence of anaerobic bacterial enzymes in metamonada in this scenario. The sister of the Preaxostyla within Metamonada represents the rest of the Eukaryotes which acquired a alphaproteobacterium.[16]

Phylogeny

In 2023, using molecular phylogenetic analysis of 186 taxa, Al Jewari and Baldauf proposed a phylogenetic tree with the metamonad Parabasalia as basal Eukaryotes. Discoba and the rest of the Eukaryota appear to have emerged as sister taxon to the Preaxostyla, incorporating a single alphaproteobacterium as mitochondria by endosymbiosis. Thus the Fornicata are more closely related to e.g. animals than to Parabasalia. The rest of the Eukaryotes emerged within the Excavata as sister of the Discoba; as they are within the same clade but are not part of the Excavata, the Excavata are in this analysis considered paraphyletic.[16]

"Excavata"

See also

Metakaryota

References

  1. ^ a b Hampl V, Hug L, Leigh JW, Dacks JB, Lang BF, Simpson AG, Roger AJ (March 2009). "Phylogenomic analyses support the monophyly of Excavata and resolve relationships among eukaryotic "supergroups"". Proceedings of the National Academy of Sciences of the United States of America. 106 (10): 3859–3864. Bibcode:2009PNAS..106.3859H. doi:10.1073/pnas.0807880106. PMC 2656170. PMID 19237557.
  2. ^ a b Simpson AG, Inagaki Y, Roger AJ (March 2006). "Comprehensive multigene phylogenies of excavate protists reveal the evolutionary positions of "primitive" eukaryotes". Molecular Biology and Evolution. 23 (3): 615–625. doi:10.1093/molbev/msj068. PMID 16308337.
  3. ^ a b Simpson AG, Patterson DJ (December 1999). "The ultrastructure of Carpediemonas membranifera (Eukaryota) with reference to the 'excavate hypothesis'". European Journal of Protistology. 35 (4): 353–370. doi:10.1016/S0932-4739(99)80044-3.
  4. ^ a b c Simpson AG (November 2003). "Cytoskeletal organization, phylogenetic affinities and systematics in the contentious taxon Excavata (Eukaryota)". International Journal of Systematic and Evolutionary Microbiology. 53 (Pt 6): 1759–1777. doi:10.1099/ijs.0.02578-0. PMID 14657103.
  5. ^ a b Dawkins R, Wong Y (2016). The Ancestor's Tale. Boston: Houghton Mifflin Harcourt. ISBN 978-0-544-85993-7.
  6. ^ a b c Cavalier-Smith T (March 2002). "The phagotrophic origin of eukaryotes and phylogenetic classification of Protozoa". International Journal of Systematic and Evolutionary Microbiology. 52 (Pt 2): 297–354. doi:10.1099/00207713-52-2-297. PMID 11931142.
  7. ^ Dawson SC, Paredez AR (February 2013). "Alternative cytoskeletal landscapes: cytoskeletal novelty and evolution in basal excavate protists". Current Opinion in Cell Biology. 25 (1): 134–141. doi:10.1016/j.ceb.2012.11.005. PMC 4927265. PMID 23312067.
  8. ^ Burki F, Roger AJ, Brown MW, Simpson AG (January 2020). "The New Tree of Eukaryotes". Trends in Ecology & Evolution. 35 (1): 43–55. doi:10.1016/j.tree.2019.08.008. PMID 31606140. S2CID 204545629.
  9. ^ Brown MW, Heiss AA, Kamikawa R, Inagaki Y, Yabuki A, Tice AK, et al. (February 2018). "Phylogenomics Places Orphan Protistan Lineages in a Novel Eukaryotic Super-Group". Genome Biology and Evolution. 10 (2): 427–433. doi:10.1093/gbe/evy014. PMC 5793813. PMID 29360967.
  10. ^ Heiss AA, Kolisko M, Ekelund F, Brown MW, Roger AJ, Simpson AG (April 2018). "Combined morphological and phylogenomic re-examination of malawimonads, a critical taxon for inferring the evolutionary history of eukaryotes". Royal Society Open Science. 5 (4): 171707. Bibcode:2018RSOS....571707H. doi:10.1098/rsos.171707. PMC 5936906. PMID 29765641.
  11. ^ Keeling PJ, Burki F (August 2019). "Progress towards the Tree of Eukaryotes". Current Biology. 29 (16): R808–R817. doi:10.1016/j.cub.2019.07.031. PMID 31430481.
  12. ^ Parfrey LW, Barbero E, Lasser E, Dunthorn M, Bhattacharya D, Patterson DJ, Katz LA (December 2006). "Evaluating support for the current classification of eukaryotic diversity". PLOS Genetics. 2 (12): e220. doi:10.1371/journal.pgen.0020220. PMC 1713255. PMID 17194223.
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