Department of Biology, Stanford University, Stanford, CA 94305;
Fakultät für Mathematik, Universität Wien, 1090 Wien, Austria.
Proc Natl Acad Sci U S A. 2017 Nov 14;114(46):E9932-E9941. doi: 10.1073/pnas.1702994114. Epub 2017 Oct 30.
Most natural populations are affected by seasonal changes in temperature, rainfall, or resource availability. Seasonally fluctuating selection could potentially make a large contribution to maintaining genetic polymorphism in populations. However, previous theory suggests that the conditions for multilocus polymorphism are restrictive. Here, we explore a more general class of models with multilocus seasonally fluctuating selection in diploids. In these models, the multilocus genotype is mapped to fitness in two steps. The first mapping is additive across loci and accounts for the relative contributions of heterozygous and homozygous loci-that is, dominance. The second step uses a nonlinear fitness function to account for the strength of selection and epistasis. Using mathematical analysis and individual-based simulations, we show that stable polymorphism at many loci is possible if currently favored alleles are sufficiently dominant. This general mechanism, which we call "segregation lift," requires seasonal changes in dominance, a phenomenon that may arise naturally in situations with antagonistic pleiotropy and seasonal changes in the relative importance of traits for fitness. Segregation lift works best under diminishing-returns epistasis, is not affected by problems of genetic load, and is robust to differences in parameters across loci and seasons. Under segregation lift, loci can exhibit conspicuous seasonal allele-frequency fluctuations, but often fluctuations may be small and hard to detect. An important direction for future work is to formally test for segregation lift in empirical data and to quantify its contribution to maintaining genetic variation in natural populations.
大多数自然种群都会受到温度、降雨或资源可利用性季节性变化的影响。季节性波动选择可能会对维持种群遗传多态性做出巨大贡献。然而，先前的理论表明，多基因座多态性的条件是有限制的。在这里，我们探索了一类更一般的模型，其中二倍体具有多基因座季节性波动选择。在这些模型中，多基因座基因型通过两步映射到适应性上。第一步映射在基因座之间是加性的，并且考虑了杂合和纯合基因座的相对贡献，即显性。第二步使用非线性适应度函数来解释选择和上位性的强度。通过数学分析和个体模拟，我们表明，如果当前有利的等位基因具有足够的显性，那么在许多基因座上稳定的多态性是可能的。这种一般机制，我们称之为“分离提升”，需要在显性方面发生季节性变化，这种现象可能在拮抗多效性和特征对适应性的相对重要性的季节性变化的情况下自然出现。分离提升在递减回报上位性下效果最佳，不受遗传负荷问题的影响，并且对基因座和季节之间参数的差异具有鲁棒性。在分离提升下，基因座可以表现出明显的季节性等位基因频率波动，但通常波动可能很小，难以检测到。未来工作的一个重要方向是在实证数据中正式检验分离提升，并量化其对维持自然种群遗传变异的贡献。
