Data from: Overdominance interacts with linkage to determine the rate of adaptation to a new optimum

Overdominance, or a fitness advantage of a heterozygote over both homozygotes, can occur commonly with adaptation to a new optimum phenotype. We model how such overdominant polymorphisms can reduce the evolvability of diploid populations, uncovering a novel form of epistatic constraint on adaptation. The fitness load caused by overdominant polymorphisms can most readily be ameliorated by evolution at tightly linked loci; therefore traits controlled by multiple loosely linked loci are predicted to be strongly constrained. The degree of constraint is also sensitive to the shape of the relationship between phenotype and fitness, and the constraint caused by overdominance can be strong enough to overcome the effects of clonal interference on the rate of adaptation for a trait. These results point to novel influences on evolvability that are specific to diploids and interact with genetic architecture, and they predict a source of stochastic variability in eukaryotic evolution experiments or cases of rapid evolution in nature.

超显性（Overdominance），指杂合子相较于两种纯合子具有更高适合度的现象，在适应新的最优表型的过程中较为常见。我们通过构建数学模型，探究这类超显性多态性如何降低二倍体种群的可演化性（evolvability），并揭示了一种全新的适应相关上位性约束（epistatic constraint）形式。超显性多态性引发的适合度负荷（fitness load），最易通过紧密连锁位点（tightly linked loci）的演化得到缓解；因此，由多个松散连锁位点调控的性状预计会受到极强的演化约束。约束程度还对表型与适合度之间的关系模式较为敏感，且超显性引发的约束强度足以抵消克隆干扰（clonal interference）对某一性状适应速率的影响。本研究结果揭示了专属于二倍体种群、且与遗传架构（genetic architecture）相互作用的全新可演化性影响因素，并预测了真核生物演化实验或自然界快速演化案例中存在的一类随机变异来源。