Diminishing returns from mutation supply rate in asexual populations

Area of Science:

• Microbial evolution
• Bacterial genetics
• Population genetics

Background:

• Mutator genotypes, with elevated mutation rates, are hypothesized to be crucial for microbial evolution.
• The supply of mutations is often considered a limiting factor for genetic adaptation.

Purpose of the Study:

• To investigate the relationship between mutation supply rate and the rate of evolutionary adaptation in experimental bacterial populations.
• To determine if increased mutation rates universally accelerate adaptive evolution or if other factors impose limits.

Main Methods:

• Utilized experimental populations of the bacterium Escherichia coli.
• Manipulated mutation supply rates to observe effects on adaptation.
• Analyzed the rate of evolutionary adaptation under different population sizes and initial adaptation states.

Main Results:

• The rate of adaptive evolution was proportional to the mutation supply rate only under specific conditions, such as in small or initially well-adapted populations.
• A distinct
• speed limit
• on adaptive evolution was observed in asexual populations.
• This speed limit was found to be independent of the mutation supply rate.

Conclusions:

• The importance of mutator genotypes in microbial evolution is context-dependent, not solely reliant on mutation supply.
• Adaptive evolution in asexual populations is subject to a fundamental speed limit.
• Factors beyond mutation supply, such as population size and initial adaptation, influence the effectiveness of increased mutation rates.