Arnold Brian J, Lahner Brett, DaCosta Jeffrey M, Weisman Caroline M, Hollister Jesse D, Salt David E, Bomblies Kirsten, Yant Levi
Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138; Center for Communicable Disease Dynamics, Department of Epidemiology, Harvard T. H. Chan School of Public Health, Boston, MA 02115;
Department of Horticulture and Landscape Architecture, Purdue University, West Lafayette, IN 47907;
Proc Natl Acad Sci U S A. 2016 Jul 19;113(29):8320-5. doi: 10.1073/pnas.1600405113. Epub 2016 Jun 29.
Serpentine barrens represent extreme hazards for plant colonists. These sites are characterized by high porosity leading to drought, lack of essential mineral nutrients, and phytotoxic levels of metals. Nevertheless, nature forged populations adapted to these challenges. Here, we use a population-based evolutionary genomic approach coupled with elemental profiling to assess how autotetraploid Arabidopsis arenosa adapted to a multichallenge serpentine habitat in the Austrian Alps. We first demonstrate that serpentine-adapted plants exhibit dramatically altered elemental accumulation levels in common conditions, and then resequence 24 autotetraploid individuals from three populations to perform a genome scan. We find evidence for highly localized selective sweeps that point to a polygenic, multitrait basis for serpentine adaptation. Comparing our results to a previous study of independent serpentine colonizations in the closely related diploid Arabidopsis lyrata in the United Kingdom and United States, we find the highest levels of differentiation in 11 of the same loci, providing candidate alleles for mediating convergent evolution. This overlap between independent colonizations in different species suggests that a limited number of evolutionary strategies are suited to overcome the multiple challenges of serpentine adaptation. Interestingly, we detect footprints of selection in A. arenosa in the context of substantial gene flow from nearby off-serpentine populations of A. arenosa, as well as from A. lyrata In several cases, quantitative tests of introgression indicate that some alleles exhibiting strong selective sweep signatures appear to have been introgressed from A. lyrata This finding suggests that migrant alleles may have facilitated adaptation of A. arenosa to this multihazard environment.
蛇纹石荒地对植物定居者来说是极端的生存挑战。这些地方的特点是孔隙率高，导致干旱、缺乏必需的矿质营养以及金属的植物毒性水平。然而，自然界中也形成了适应这些挑战的种群。在这里，我们采用基于种群的进化基因组学方法并结合元素分析，来评估同源四倍体砂生拟南芥是如何适应奥地利阿尔卑斯山多重重挑战的蛇纹石栖息地的。我们首先证明，适应蛇纹石环境的植物在常见条件下表现出显著改变的元素积累水平，然后对来自三个种群的24个同源四倍体个体进行重测序以进行基因组扫描。我们发现了高度局部化的选择性清除的证据，这表明蛇纹石适应具有多基因、多性状基础。将我们的结果与之前对英国和美国亲缘关系密切的二倍体琴叶拟南芥独立蛇纹石定殖的研究进行比较，我们发现在11个相同位点上具有最高水平的分化，为介导趋同进化提供了候选等位基因。不同物种独立定殖之间的这种重叠表明，有限数量的进化策略适合于克服蛇纹石适应的多重挑战。有趣的是，我们在砂生拟南芥中检测到选择的印记，其背景是来自附近非蛇纹石砂生拟南芥种群以及琴叶拟南芥的大量基因流。在几个案例中，渗入的定量测试表明，一些表现出强烈选择性清除特征的等位基因似乎是从琴叶拟南芥渗入的。这一发现表明，迁移等位基因可能促进了砂生拟南芥对这种多危险环境的适应。
