Changes in mitochondrial genetic codes as phylogenetic characters: two examples from the flatworms.

Area of Science:

• Molecular Biology
• Evolutionary Biology
• Genetics

Background:

• Phylogenetic information can be derived from shared molecular genetic characteristics beyond DNA and protein sequences.
• Complex and rare genetic traits are valuable for establishing evolutionary relationships due to their low probability of convergent evolution.

Purpose of the Study:

• To define a clade within the Platyhelminthes (flatworms) using specific changes in the mitochondrial genetic code.
• To investigate the phylogenetic distribution of standard and variant genetic codes within metazoans.

Main Methods:

• Analysis of mitochondrial genetic code variations, specifically codon assignments for AAA and AUA.
• Sampling of 10 distinct classes within the Rhabditophora and comparison with Acoela, Nemertodermatida, and Catenulida.
• Development of a rapid computerized method for genetic code analysis.

Main Results:

• Identified a novel clade, Rhabditophora, characterized by AAA coding for Asn and AUA coding for Ile in their mitochondrial genetic code.
• Confirmed that the codon UAA functions as a standard stop codon, not coding for Tyr, in Platyhelminthes.
• Excluded Acoela, Nemertodermatida, and Catenulida from the Rhabditophora clade based on their standard invertebrate codon assignments.
• Demonstrated the broad phylogenetic distribution of the standard invertebrate code and confirmed known metazoan deviations.

Conclusions:

• The Rhabditophora, a diverse group including turbellarians and Neodermata, are defined by specific mitochondrial genetic code alterations.
• The study provides robust evidence for the exclusion of Acoela, Nemertodermatida, and Catenulida from the Rhabditophora.
• The developed method facilitates rapid analysis of genetic codes, aiding in phylogenetic studies across metazoans.