Parallel Evolution of Metazoan Mitochondrial Proteins

Area of Science:

• Evolutionary biology
• Molecular evolution
• Phylogenetics

Background:

• Amino acid propensities at specific sites change over evolutionary time.
• These changes are driven by factors like epistasis and environmental shifts.
• Such dynamics influence the fixation probabilities of different amino acids and can increase homoplasy rates.

Purpose of the Study:

• To investigate the relationship between evolutionary time and the rates of homoplasy versus divergent substitution.
• To determine if changes in fitness landscapes correlate with the rate of amino acid evolution.

Main Methods:

• Phylogenetic reconstruction of twelve mitochondrial proteins across thousands of metazoan species.
• Measurement of phylogenetic distances at which homoplasies and divergent substitutions occur.
• Analysis comparing the distances for parallel versus divergent substitutions.

Main Results:

• The mean phylogenetic distance between parallel substitutions is approximately 20% lower than that for divergent substitutions.
• This indicates a higher likelihood of a fixed variant being deleterious in more remote species compared to closely related ones.
• Findings remain robust despite potential phylogenetic reconstruction artifacts or site pooling.

Conclusions:

• Fitness landscapes at single amino acid positions evolve at rates comparable to amino acid changes themselves.
• The observed pattern of homoplasy rates supports the dynamic nature of evolutionary constraints.
• This implies that the selective environment or interactions influencing amino acid fixation are not static over long evolutionary timescales.