The opisthokonts () are a broad group of , including both the animal and fungus kingdoms.
Flagella and other characteristics
A common characteristic of opisthokonts is that
flagellate cells, such as the
spermatozoon of most animals and the
zoospore of the
chytrid fungi, propel themselves with a single
posterior flagellum. It is this feature that gives the group its name. In contrast, flagellate cells in other eukaryote groups propel themselves with one or more
anterior flagella. Flagellate cells however have been secondarily lost in some opisthokont groups, including most of the fungi.
Opisthokont characteristics include synthesis of extracellular chitin in exoskeleton, cyst/spore wall, or cell wall of filamentous growth and hyphae; the extracellular digestion of substrates with osmotrophic absorption of nutrients; and other cell biosynthetic and metabolic pathways. Opisthokonts were amoeboid and phagocytosis.
History
The close relationship between animals and fungi was suggested by Thomas Cavalier-Smith in 1987,
who used the informal name opisthokonta (the formal name has been used for the
Chytridiomycota by Herbert Copeland in 1956), and was supported by later genetic studies.
Early phylogenies placed fungi near the and other groups that have mitochondrion with flat cristae, but this character varies. More recently, it has been said that holozoa (animals) and holomycota (fungi) are much more closely related to each other than either is to plants, because opisthokonts have a triple fusion of carbamoyl phosphate synthetase, dihydroorotase, and aspartate carbamoyltransferase that is not present in plants, and plants have a fusion of thymidylate synthase and dihydrofolate reductase not present in the opisthokonts. Animals and fungi are also more closely related to amoebas than to plants, and plants are more closely related to the SAR supergroup of protists than to animals or fungi. Animals and fungi are both heterotrophs, unlike plants, and while most fungi are sessile like plants, there are also sessile animals.
Cavalier-Smith and Alexandra Stechmann argue that the uniciliate eukaryotes such as opisthokonts and Amoebozoa, collectively called , split off from the other biciliate eukaryotes, called , shortly after they Evolution.
Taxonomy
Opisthokonts are divided into
Holomycota or Nucletmycea (fungi and all organisms more closely related to fungi than to animals) and
Holozoa (animals and all organisms more closely related to animals than to fungi); no opisthokonts basal to the Holomycota/Holozoa split have yet been identified as of 2020.
The Opisthokonts was largely resolved by Guifré Torruella et al. (2015) using phylogenomics (comparison of many conserved protein loci from genomes).
Holomycota and Holozoa are composed of the following groups (see § Phylogeny for more citations):
Phylogeny
The following phylogenetic tree indicates the evolutionary relationships between the different opisthokont lineages, and the time divergence of the clades in millions of years ago (Mya). Sources:
-
Holomycota: Tedersoo et al. (2018) 16S,
-
Holozoa: Tikhonenkov et al. (2020) phylogenomic.
Notes:
-
The location of Tunicaraptor is not completely resolved in Tikhonenkov et al. (2020). The possibilities of it being sister to all other Holozoa or being sister to Filasteria have not been ruled out.
-
Torruella et al. (2015) instead places Corallochytrium as sister to Ichthyosporea, forming the clade Teretosporea.
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Gallery
File:Nuclearia sp Nikko.jpg| Nuclearia (Nucleariida)
File:Rozella allomycis2.jpg| Rozella sp. (Rozellida)
File:Msp tubule EM.jpg|Microsporidian spore (Microsporidia)
File:CSIRO ScienceImage 1392 Scanning Electron Micrograph of Chytrid Fungus.jpg|Chytrid (flagellated fungus)
File:Sphaeroforma arctica.jpg| Sphaeroforma sp. (Mesomycetozoea)
File:Ministeria vibrans.jpeg| Ministeria sp. (Filasterea)
File:Capsaspora owczarzaki.jpeg| Capsaspora sp. (Filasterea)
File:Protero-7.png| Salpingoeca (Choanoflagellatea)
File:Desmarella moniliformis.jpg| Desmarella sp. colony (Choanoflagellatea)
File:Matsutakeredpinemushroomhunting.jpg|Two opisthokonts: a human (Metazoa) and a mushroom (Fungi)
External links
