Eukaryotes' Closest Relatives?

[lpetrich]

The authors did ancestral-state reconstructions with several high-level phylogenies, since that is still not very well-settled. In their diagram, they have

LECA -- mito - multi - nopp - closed - sex

• Discoba (in Excavata) -- mito - ? - ? - ? - sex
• Metamonada (in Excavata) -- h2some - multi - ? - closed - sex
• Amorphea / Obazoa / Opimoda -- mito - multi - ? - closed - sex
  • Amoebozoa -- mito - multi - pp - closed - sex
  • Opisthokonta -- mito - multi - nopp - closed - sex
    • Fungi -- mito - multi - nopp - closed - sex
    • Metazoa (animals) --mito - multi - ? - ? - sex
• Diaphoretickes / Diphoda -- mito - multi - nopp - closed - sex
  • Cryptista (in Hacrobia) -- mito - nomulti - nopp - ? - nosex
  • Haptista (in Hacrobia) -- mito - nomulti - nopp - ? - nosex
  • Archaeplastida -- mito - ? - nopp - ? - sex
    • Glaucophyta -- mito - multi - nopp - open - nosex
    • Rhodophyta (red algae) -- mito - nomulti - nopp - closed - sex
    • Chloroplastida (green algae) -- mito - nomulti - nopp - ? - sex
      • Chlorophyta -- mito - nomulti- nopp - closed - sex
      • Streptophyta (incl. land plants) -- mito - nomulti - nopp - open - sex
  • SAR clade -- mito - multi - nopp - closed - sex
    • Rhizaria -- mito - multi - (pp) - closed - sex
    • SA clade -- mito - multi - nopp - closed - sex
      • Alveolata -- mito - multi - nopp - closed - sex
      • Stramenopiles -- mito - multi - nopp - closed - sex
  
  With ancestral-state reconstruction, the authors found that the last eukaryotic common ancestor (LECA) was multinucleate, as were all the supergroups but Hacrobia. The LECA also had mitochondria, sex (meiosis-cell-fusion cycle), and closed division. It did not have the authors' restriction of polyploidy, however, meaning that it did ordinary reproduction as a haploid. Ordinary reproduction as a diploid is something that was invented several times, as was open division, and reduction of mitochondria to hydrogenosomes and the like. The LECA did not have plastids, something evident from their scattered distribution.

 

[lpetrich]

The authors discussed "Conflict and Co-operation in a Syncytial LECA" then "Origins of Flagellated Eukaryotes".

As to cooperation, in a multinucleate cell, one nucleus can fill in for another one if some of its genetic material become damaged or deleted.

The authors conclude that the LECA had a single-nucleus flagellated phase that alternated with a multinuclear phase as a way of distributing itself, and they propose that the eukaryote flagellum is an extension of a bit of cytoskeleton outside of the cell body.