Abstract
Antagonistic selection between different fitness components (e.g., survival versus fertility) or different types of individuals in a population (e.g., females versus males) can potentially maintain genetic diversity and thereby account for the high levels of fitness variation observed in natural populations. However, the degree to which antagonistic selection can maintain genetic variation critically depends on the dominance relations between antagonistically selected alleles in diploid individuals. Conditions for stable polymorphism of antagonistically selected alleles are narrow, particularly when selection is weak, unless the alleles exhibit “dominance reversals”—in which each allele is partially or completely dominant in selective contexts in which it is favored and recessive in contexts in which it is harmful. Although theory predicts that dominance reversals should emerge under biologically plausible conditions, evidence for dominance reversals is sparse. In this primer, we review theoretical arguments and data supporting a role for dominance reversals in the maintenance of genetic variation. We then highlight an illuminating new study by Grieshop and Arnqvist, which reports a genome-wide signal of dominance reversals between male and female fitness in seed beetles.
Highlights
Evolution by natural selection requires heritable variation for traits affecting fitness
According to the mutation-selection balance hypothesis, variation is maintained at an equilibrium between recurrent mutation, which generates a steady stream of new, deleterious genetic variation, and natural selection which removes it
These doubts reflect the current deficit of clear-cut examples of balanced polymorphisms [19] and unanswered questions about the potential for specific mechanisms of balancing selection to account for broad-scale patterns of variation in fitness traits (e.g., [16])
Summary
The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
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