Bikont

Bikonts
A radiolarian
Scientific classification
Domain: Eukaryota
(unranked): Bikonta
Cavalier-Smith, 1993
Subgroups
Synonyms
  • Biciliata Cavalier-Smith, 1993
  • Diaphoretickes Adl et al., 2012
  • Diphoda Derelle et al., 2015

A bikont ("two flagella") is any of the eukaryotic organisms classified in the group Bikonta. Many single-celled and multi-celled organisms are members of the group, and these, as well as the presumed ancestor, have two flagella.

Enzymes

Another shared trait of bikonts is the fusion of two genes into a single unit: the genes for thymidylate synthase (TS) and dihydrofolate reductase (DHFR) encode a single protein with two functions.

The genes are separately translated in unikonts.

Relationships

Some research suggests that a unikont (a eukaryotic cell with a single flagellum) was the ancestor of opisthokonts (Animals, Fungi, and related forms) and Amoebozoa, and a bikont was the ancestor of Archaeplastida (Plants and relatives), Excavata, Rhizaria, and Chromalveolata. Cavalier-Smith has suggested that Apusozoa, which are typically considered incertae sedis, are in fact bikonts.

Relationships within the bikonts are not yet clear. Cavalier-Smith has grouped the Excavata and Rhizaria into the Cabozoa and the Archaeplastida and Chromalveolata into the Corticata, but at least one other study has suggested that the Rhizaria and Chromalveolata form a clade.

An alternative to the Unikont–Bikont division was suggested by Derelle et al. in 2015, where they proposed the acronyms OpimodaDiphoda respectively, as substitutes to the older terms. The name Diphoda is formed from the letters of DIscoba and diaPHOretickes (shown in capitals). [suggested singular forms are Opneme-Dipheme respectively]

Cladogram

A "classical" cladogram (data from 2012, 2015) is:

Eukaryotes
Bikonta
SAR/HA Supergroup

Archaeplastida (inc. land plants)

Cryptophyta

Haptophyta

SAR supergroup

Rhizaria

Halvaria

Heterokont

Alveolata

Excavata

Unikonta

However, a cladogram (data from 2015, 2016) with the root in Excavata is

Eukaryotes
Diphoda (Bikonts)
SAR/HA Supergroup

Archaeplastida (inc. land plants)

Chromista
Hacrobia

Cryptista

Haptista

Harosa

Rhizaria

Halvaria

Heterokonta

Alveolata

Metamonada?

Opimoda (Unikonts)

Metamonada?

podiates

Neolouka

Collodictyon

Varisulca

Amoebozoa

Obazoa

Apusomonadida

Breviata

Opisthokonta

The corticates correspond roughly to the bikonts. While Haptophyta, Cryptophyta, Glaucophyta, Rhodophyta, the SAR supergroup and viridiplantae are usually considered monophyletic, Archaeplastida may be paraphyletic, and the mutual relationships between these phyla are still to be fully resolved.

Recent reconstructions placed Archaeplastida and Hacrobia together in an "HA supergroup" or "AH supergroup", which was a sister clade to the SAR supergroup within the SAR/HA supergroup. However, this seems to have fallen out of favor as the monophyly of hacrobia has come under dispute.

See also


This page was last updated at 2024-02-17 04:27 UTC. Update now. View original page.

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