Polygenic variation maintained by balancing selection: pleiotropy, sex-dependent allelic effects and G x E...

Area of Science:

• Evolutionary genetics
• Quantitative genetics
• Population genetics

Background:

• Maintaining polygenic variation is crucial for adaptation.
• Previous models proposed balancing selection, genotype-by-environment (G x E) interactions, and sex-dependent effects to preserve variation.

Purpose of the Study:

• To investigate three selection-based scenarios for maintaining polygenic variation.
• To analyze the conditions under which pleiotropic balancing selection, G x E interactions, and sex-dependent effects preserve genetic diversity.
• To explore the dynamics of allele frequencies and stable equilibria under these scenarios.

Main Methods:

• Mathematical modeling of an additive polygenic trait with n diallelic loci under stabilizing selection.
• Analysis of equilibria where the population mean deviates from the optimum.
• Numerical exploration of allele-frequency dynamics and properties of stable equilibria.

Main Results:

• Under weak selection, all three models exhibit similar approximate allele-frequency dynamics.
• Pleiotropic balancing selection maintains variation only when balancing selection strength exceeds stabilizing selection strength.
• Spatial and temporal G x E interactions can maintain variation if the coefficient of variation in allelic effects is sufficiently high and correlations between loci are not excessively positive.

Conclusions:

• Polymorphism requires the population mean to be close to the optimum to prevent directional selection from overwhelming balancing selection.
• Sex-dependent allelic effects are unlikely to maintain polygenic variation due to constraints on correlations between loci.
• The findings provide insights into mechanisms preserving genetic variation in evolving populations.