Evolution of dominance under frequency-dependent intraspecific competition

Area of Science:

• Population Genetics
• Evolutionary Biology
• Quantitative Genetics

Background:

• Frequency-dependent disruptive selection shapes quantitative traits due to resource competition.
• A modifier locus influences the degree of dominance at a primary trait locus.

Purpose of the Study:

• Analyze invasion and fixation conditions for modifier alleles.
• Investigate the impact of modifier effect size and deleterious fitness effects.
• Explore the role of linkage on evolutionary dynamics.

Main Methods:

• Population-genetic analysis of a two-locus, two-allele model.
• Mathematical modeling of allele invasion, fixation, and equilibrium dynamics.
• Examination of frequency-dependent and frequency-independent fitness effects.

Main Results:

• Modifier invasion conditions are generally more restrictive than fixation conditions.
• Larger effect modifiers have broader invasion and fixation parameter ranges.
• Deleterious modifiers can invade with sufficient dominance induction and selection strength.
• Linkage affects the rate of spread but not the invasion/fixation conditions.
• Successful invasion implies global fixation, but deleterious modifiers may reach stable intermediate frequencies.

Conclusions:

• Dominance evolution can efficiently remove unfit heterozygotes under balancing selection.
• Invasion analysis of small-effect mutants is insufficient for understanding frequency-dependent selection dynamics.
• Modifier loci play a crucial role in shaping adaptation under complex selective pressures.