Waiting for a compensatory mutation: phase zero of the shifting-balance process

Area of Science:

• Evolutionary biology
• Population genetics

Background:

• Highly integrated genetic systems require coordinated mutations for fitness.
• Wright's shifting-balance theory explains evolution beyond natural selection alone.

Purpose of the Study:

• Analyze the impact of waiting time for new mutations in the shifting-balance theory.
• Investigate factors limiting the fixation of compensatory mutations.

Main Methods:

• Theoretical analysis of mutation fixation times.
• Modeling the role of selection relaxation and linkage.

Main Results:

• The average time for double fixation of compensatory mutations is extremely long.
• Selection is too effective in large populations, and mutations too rare in small ones.
• Relaxation of selection allows mutations to reach moderate frequencies, reducing fixation time.

Conclusions:

• The waiting time for new mutants (phase zero) is a major limitation for the shifting-balance process.
• Relaxing selection is a plausible mechanism for compensatory mutation fixation.
• The probability of fixation remains small, especially with low initial allele frequencies.