Codon volatility as an indicator of positive selection: data from eukaryotic genome comparisons

Area of Science:

• Evolutionary Biology
• Genomics
• Molecular Biology

Background:

• Codon volatility, defined as the proportion of a codon's point-mutation neighbors encoding different amino acids, has been proposed as an indicator of past positive selection.
• Understanding the evolutionary pressures shaping genomes is crucial for deciphering biological complexity.

Purpose of the Study:

• To investigate the relationship between codon volatility and patterns of nucleotide substitution.
• To determine if codon volatility accurately reflects positive selection across different species.

Main Methods:

• Genome-wide comparison of orthologous genes between three pairs of related species: Plasmodium falciparum/P. yoelii (protists), Saccharomyces cerevisiae/S. paradoxus (fungi), and mouse/rat (mammals).
• Analysis of synonymous and nonsynonymous nucleotide substitution rates in relation to codon volatility.

Main Results:

• Codon volatility did not consistently correlate with an elevated rate of nonsynonymous substitution, contrary to expectations for positive selection.
• The strongest association found was between codon volatility and nucleotide content at the second codon position.
• This finding aligns with the inherent properties of the genetic code.

Conclusions:

• Codon volatility may not be a reliable index for detecting past positive selection in genome-wide analyses.
• Nucleotide composition, particularly at the second codon position, is a significant factor influencing codon volatility.
• Further research is needed to identify robust molecular signatures of positive selection.