Should we expect substitution rate to depend on population size?

Area of Science:

• Evolutionary Biology
• Population Genetics

Background:

• The rate of nucleotide substitution is often considered a decreasing function of effective population size, particularly for nonsynonymous mutations.
• This view is largely based on models of slightly deleterious mutations, but realistic models must also account for advantageous mutations.

Purpose of the Study:

• To present an alternative model predicting minimal population size effect on nucleotide substitution rates.
• To investigate the role of concave log-fitness functions and fixed mutational effect distributions.

Main Methods:

• Development of a theoretical model incorporating concave log-fitness functions.
• Simulation of a specific instance of the proposed model.

Main Results:

• The model predicts near-absence of a population size effect on the nucleotide substitution rate.
• Simulations confirm the approximate insensitivity of substitution rates to population size.
• Existing experimental evidence for a population size effect is largely equivocal and suggests a very small effect.

Conclusions:

• The proposed model offers an alternative explanation for nucleotide substitution rates.
• The population size effect on substitution rates may be gene-specific and smaller than previously assumed.