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      Range Expansion Compromises Adaptive Evolution in an Outcrossing Plant.

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          Abstract

          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.

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          Author and article information

          Journal
          Curr. Biol.
          Current biology : CB
          Elsevier BV
          1879-0445
          0960-9822
          Aug 21 2017
          : 27
          : 16
          Affiliations
          [1 ] Department of Ecology and Evolution, University of Lausanne, 1015 Lausanne, Switzerland; BIOGECO, INRA, University of Bordeaux, 33610 Cestas, France. Electronic address: santiago.gonzalez-martinez@inra.fr.
          [2 ] Department of Ecology and Evolution, University of Lausanne, 1015 Lausanne, Switzerland.
          Article
          S0960-9822(17)30865-5
          10.1016/j.cub.2017.07.007
          28803874
          310ebf62-ef73-4c69-a5e4-5c8d30f221fc
          History

          Mercurialis annua,colonization,deleterious mutation,dispersal,population structure,positive selection,selective sweep,site frequency spectrum

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