Deleterious mutations, apparent stabilizing selection and the maintenance of quantitative variation.

Area of Science:

• Evolutionary genetics
• Quantitative genetics

Background:

• Apparent stabilizing selection on quantitative traits can be caused by pleiotropic effects of deleterious mutations.
• Individuals with extreme trait values may carry more deleterious alleles, leading to apparent selection.
• Previous analyses did not fully account for epistatic selection against deleterious alleles.

Purpose of the Study:

• To model the dependence of apparent stabilizing selection on genomic deleterious mutation rate (U) and mutation load (K).
• To investigate the role of epistatic selection against deleterious alleles.
• To determine the intensity of apparent stabilizing selection and its relationship to mutation parameters.

Main Methods:

• Developed a simple model incorporating genomic deleterious mutation rate, mutation load distribution, and directional selection parameters.
• Allowed for epistatic selection against deleterious alleles.
• Analyzed the distribution of breeding values and apparent fitness functions under various selection scenarios.

Main Results:

• The distribution of mutation load (K), breeding values, and apparent stabilizing selection functions are nearly Gaussian under realistic parameters.
• The intensity of apparent selection (beta) is closely related to the selection coefficient against individual deleterious mutations (s = U/k).
• Appreciable apparent stabilizing selection is predicted when s > 0.03, consistent with existing data.

Conclusions:

• Pleiotropic effects of unconditionally deleterious mutations can generate significant apparent stabilizing selection.
• The model predicts a relationship between apparent selection intensity and mutation parameters, offering insights into the maintenance of genetic variation.
• Further experiments are suggested to differentiate selection due to pleiotropy from direct selection on the trait.