Department of Ecology and Evolution, University of Lausanne, 1015 Lausanne, Switzerland; BIOGECO, INRA, University of Bordeaux, 33610 Cestas, France.
Department of Ecology and Evolution, University of Lausanne, 1015 Lausanne, Switzerland.
Curr Biol. 2017 Aug 21;27(16):2544-2551.e4. doi: 10.1016/j.cub.2017.07.007. Epub 2017 Aug 10.
Neutral genetic diversity gradients have long been used to infer the colonization history of species [1, 2], but range expansion may also influence the efficacy of natural selection and patterns of non-synonymous polymorphism in different parts of a species' range [3]. Recent theory predicts both an accumulation of deleterious mutations and a reduction in the efficacy of positive selection as a result of range expansion [4-8]. These signatures have been sought in a number of studies of the human range expansion out of Africa, but with contradictory results [9-14]. We analyzed the polymorphism patterns of 578,125 SNPs (17,648 genes) in the European diploid plant Mercurialis annua, which expanded its range from an eastern Mediterranean refugium into western habitats with contrasted climates [15]. Our results confirmed strong signatures of bottlenecks and revealed the accumulation of mildly to strongly deleterious mutations in range-front populations. A significantly higher number of these mutations were homozygous in individuals in range-front populations, pointing to increased genetic load and reduced fitness under a model of recessive deleterious effects. We also inferred a reduction in the number of selective sweeps in range-front versus core populations. These signatures have persisted even in a dioecious herb subject to substantial interpopulation gene flow [15]. Our results extend support from humans to plants for theory on the dynamics of mutations under selection during range expansion, showing that colonization bottlenecks can compromise adaptive potential.
中性遗传多样性梯度长期以来一直被用于推断物种的殖民历史[1,2]，但范围扩张也可能影响物种不同区域的自然选择效果和非同义多态性模式[3]。最近的理论预测，由于范围扩张，会积累有害突变，并降低正选择的效率[4-8]。这些特征已经在对人类从非洲向外扩张的许多研究中进行了研究，但结果却相互矛盾[9-14]。我们分析了欧洲二倍体植物 Mercurialis annua 中 578,125 个 SNP（17,648 个基因）的多态性模式，该植物从东地中海避难所扩展到具有不同气候的西部栖息地[15]。我们的结果证实了瓶颈的强烈特征，并揭示了在范围前沿种群中积累了轻度至强烈有害的突变。在隐性有害效应模型下，这些突变的纯合个体数量在范围前沿种群中显著增加，这表明遗传负荷增加，适应度降低。我们还推断出范围前沿与核心种群之间选择清扫的数量减少。即使在受大量种群间基因流影响的雌雄异株草本植物中，这些特征仍然存在[15]。我们的结果从人类扩展到植物，为范围扩张过程中选择下突变动态的理论提供了支持，表明殖民瓶颈会损害适应潜力。
