Data from: Spatially and temporally varying selection on intrapopulation quantitative trait loci for a life history trade-off in Mimulus guttatus

Why do populations remain genetically variable despite strong continuous natural selection? Mutation reconstitutes variation eliminated by selection and genetic drift, but theoretical and experimental studies each suggest that mutation-selection balance insufficient to explain extant genetic variation in most complex traits. The alternative hypothesis of balancing selection, wherein selection maintains genetic variation, is an aggregate of multiple mechanisms (spatial and temporal heterogeneity in selection, frequency-dependent selection, antagonistic pleiotropy, etc.). Most of these mechanisms have been demonstrated for Mendelian traits, but there is little comparable data for loci affecting quantitative characters. Here, we report a three-year field study of selection on intra-population Quantitative Trait Loci (QTL) of flower size, a highly polygenic trait of Mimulus guttatus. The QTL exhibit antagonistic pleiotropy: alleles that increase flower size reduce viability but increase fecundity. The magnitude and direction of selection fluctuates yearly and on a spatial scale of meters. This study provides direct evidence of balancing selection mechanisms on QTL of an ecologically relevant trait.

为何在持续强烈的自然选择作用下，种群仍能维持遗传变异？突变重建了被选择与遗传漂变清除的遗传变异，但理论与实验研究均表明，突变-选择平衡（mutation-selection balance）不足以解释多数复杂性状中现存的遗传变异。主张选择维持遗传变异的平衡选择假说，整合了多种作用机制，包括选择的时空异质性、频率依赖型选择、拮抗多效性等。这类机制多数已在孟德尔性状中得到验证，但针对影响数量性状的基因座，类似的研究数据却十分匮乏。本研究针对亮黄沟酸浆（Mimulus guttatus）这一高度多基因调控的花大小性状，开展了为期三年的野外研究，分析其种群内数量性状基因座（Quantitative Trait Loci, QTL）上的选择作用。该类QTL表现出拮抗多效性：增大花尺寸的等位基因会降低个体存活力，却能提升繁殖力。选择作用的强度与方向在年度间以及米级空间尺度上均存在波动。本研究为生态相关性状的QTL上存在平衡选择机制提供了直接证据。