Phylogenetic analysis based on rRNA sequences supports the archaebacterial rather than the eocyte tree.

Area of Science:

• Molecular Evolution
• Phylogenetics
• Genomics

Background:

• The fundamental question of life's primary lineages and their evolutionary relationships remains highly debated.
• Two prominent models exist: the 'archaebacterial tree' (Archaebacteria, Eubacteria, Eukaryotes) and the 'eocyte tree' (grouping eocytes with eukaryotes).
• Previous support for the eocyte tree stemmed from analyses of small subunit ribosomal RNA (rRNA) using the evolutionary parsimony method.

Purpose of the Study:

• To re-evaluate the evolutionary relationships of life's primary lineages using robust phylogenetic methods.
• To compare the performance of different phylogenetic methods (evolutionary parsimony, neighbor-joining, maximum parsimony) in reconstructing evolutionary trees.
• To resolve the controversy between the archaebacterial and eocyte tree models.

Main Methods:

• Analysis of small subunit ribosomal RNA (rRNA) gene sequences using neighbor-joining and maximum parsimony methods.
• Computer simulations to assess the reliability of phylogenetic methods in recovering known evolutionary trees.
• Analysis of large subunit rRNA sequences using neighbor-joining, maximum parsimony, and evolutionary parsimony methods.

Main Results:

• Analyses of small subunit rRNA data using neighbor-joining and maximum parsimony methods strongly favor the archaebacterial tree.
• Computer simulations demonstrated high recovery rates (>90%) for both the archaebacterial and eocyte trees using neighbor-joining and maximum parsimony, but low rates for evolutionary parsimony.
• Analysis of large subunit rRNA sequences by all three methods unequivocally supported the archaebacterial tree.

Conclusions:

• The archaebacterial tree, proposing Archaebacteria, Eubacteria, and Eukaryotes as primary lineages, is strongly supported by current phylogenetic analyses.
• The evolutionary parsimony method may be less reliable for reconstructing deep evolutionary divergences compared to neighbor-joining and maximum parsimony.
• This study provides robust evidence favoring a specific model for the early evolution of life.