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Partial protection from cyclical selection generates a high level of polymorphism at multiple non-neutral sites
Yeongseon Park1, Yuseob Kim1,2
1Division of EcoScience, Ewha Womans University, Seoul, Korea.
Summary
Seasonal fluctuations in selection can maintain genetic diversity (polymorphism) at multiple gene locations. This occurs even without a refuge, leading to increased nonneutral polymorphism and potentially a high nonsynonymous-to-synonymous ratio in protein-coding genes.
Area of Science:
- Evolutionary genetics
- Population genetics
- Theoretical biology
Background:
- Temporally varying selection can maintain genetic polymorphism, but the
- storage effect
- (population refuge) greatly enhances this.
- Investigating seasonal selection's role in polymorphism maintenance without refuges is crucial.
Purpose of the Study:
- To determine if seasonally fluctuating selection can sustain polymorphism at multiple genetic loci.
- To explore the impact of such selection on allele frequencies and overall polymorphism levels.
- To assess the effect on linked neutral sites and the nonsynonymous-to-synonymous ratio.
Main Methods:
- Modeling a phenotype with a seasonally oscillating optimum determined by multiple alleles.
- Analyzing the distribution of mutation effects across these alleles.
- Simulating scenarios with randomly perturbed environmental oscillations.
Main Results:
- Long-term polymorphism was maintained at multiple sites with heavy allele frequency oscillations.
- The level of nonneutral polymorphism significantly increased.
- Polymorphism at linked neutral sites varied, and the nonsynonymous-to-synonymous ratio in protein-coding sequences may exceed one.
- Randomly perturbed oscillations reduced the likelihood of trans-species polymorphism.
Conclusions:
- Seasonally fluctuating selection, even without refuges, can effectively maintain long-term genetic polymorphism at multiple loci.
- This mechanism leads to substantial nonneutral polymorphism and can influence patterns of molecular evolution.
- The findings challenge the universality of trans-species polymorphism as a sole indicator of balancing selection.
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