Unikonts Include Protists That Are Closely Related to Fungi and Animals

Rucete ✏ Campbell Biology In a Nutshell

Unit 5 THE EVOLUTIONARY HISTORY OF BIOLOGICAL DIVERSITY — Concept 28.5 Unikonts Include Protists That Are Closely Related to Fungi and Animals

The Unikonta supergroup is one of the four major clades of eukaryotes and includes animals, fungi, and closely related protists. It is subdivided into two major groups: amoebozoans and opisthokonts, both supported by molecular and structural evidence.

What Are Unikonts?

• Include animals, fungi, and protists such as slime molds, tubulinids, entamoebas, nucleariids, and choanoflagellates.
• Divided into:
  • Amoebozoans (e.g., tubulinids, slime molds)
  • Opisthokonts (e.g., animals, fungi, and close relatives)
• May represent the earliest-diverging eukaryotic supergroup.

Amoebozoans

• Lobe- or tube-shaped pseudopodia distinguish them from other amoebas.
• Subgroups include:

1. Tubulinids

• Common in soil, freshwater, and marine environments.
• Unicellular heterotrophs that consume bacteria and detritus.
• Example: Amoeba proteus.

2. Slime Molds

• Resemble fungi (due to fruiting bodies) but evolved independently.
• Two types:
  • Plasmodial slime molds:
    • Form a large, multinucleate plasmodium.
    • Feed via phagocytosis.
    • Produce fruiting bodies when conditions worsen.
  • Cellular slime molds:
    • Live as solitary amoebas; aggregate into a slug-like body under stress.
    • Form asexual fruiting bodies.
    • Cell recognition prevents cheaters from exploiting cooperation.

3. Entamoebas

• Mostly parasites of vertebrates and invertebrates.
• Entamoeba histolytica causes amoebic dysentery.

Opisthokonts

• Include animals, fungi, and related protists.
• Key protists:
  • Choanoflagellates: Closest living relatives of animals.
  • Nucleariids: Closest relatives of fungi.
• Help explain the abandonment of the Protista kingdom due to closer ties to multicellular life forms.

Root of the Eukaryotic Tree

• Studies use genes from alpha-proteobacteria (mitochondrial origin) to infer early eukaryotic evolution.
• Suggest Unikonta diverged first, placing the eukaryotic root between Unikonta and the rest.
• This hypothesis is still under active investigation.

In a Nutshell

Unikonts include amoebozoans (with lobe-shaped pseudopodia) and opisthokonts (which include fungi, animals, and close protists). Their diversity and evolutionary links to multicellular life challenge older taxonomies and support a dynamic view of early eukaryotic evolution.