Data from: Ecotypes of an ecologically dominant prairie grass (Andropogon gerardii) exhibit genetic divergence across the U.S. Midwest grasslands environmental gradient

Big bluestem (Andropogon gerardii) is an ecologically dominant grass with wide distribution across the environmental gradient of U.S. Midwest grasslands. This system offers an ideal natural laboratory to study the nature of population divergence and adaptation in spatially varying climates. Objectives were to: (i) characterize neutral genetic diversity and structure within and among three regional ecotypes derived from 11 prairies across the U.S. Midwest environmental gradient, (ii) distinguish between the relative roles of isolation-by-distance (IBD) vs. isolation-by-environment (IBE) on ecotype divergence, (iii) identify outlier loci under selection, and (iv) assess the association between outlier loci and climate. Using two primer sets, we genotyped 378 plants at 384 polymorphic AFLP loci across regional ecotypes from central and eastern Kansas, and Illinois. Neighbor-joining tree and PCA revealed strong genetic differentiation between Kansas and Illinois ecotypes, which was better explained by IBE than IBD. High genetic variability within prairies was found (80%) and even fragmented Illinois prairies, surprisingly, contain high within-prairie genetic diversity (92%). Using Bayenv2, we identified 14 top-ranked outlier loci among ecotypes to be associated with temperature and precipitation variables. Six of seven BayeScan FST-outliers were also found in common with Bayenv2 outliers. High genetic diversity may enable big bluestem populations to better withstand changing climates; however, population divergence supports the use of local ecotypes in grassland restoration. Knowledge of genetic variation in this ecological dominant and other grassland species will be critical to understanding grassland response and restoration challenges in the face of a changing climate.

大须芒草（Andropogon gerardii）是一种生态主导型草本物种，广泛分布于北美中西部草原的环境梯度中。该物种为研究空间异质气候下的种群分化与适应本质提供了理想的天然实验平台。本研究的目标如下：（1）对源自北美中西部环境梯度内11个草原的3个区域生态型，刻画其种群内及种群间的中性遗传多样性与遗传结构；（2）区分距离隔离（isolation-by-distance, IBD）与环境隔离（isolation-by-environment, IBE）在生态型分化中的相对作用；（3）鉴定受选择的异常位点；（4）评估异常位点与气候因子之间的关联。本研究使用2组引物，对采自堪萨斯州中部、东部以及伊利诺伊州的区域生态型共378株个体完成了384个多态性扩增片段长度多态性（AFLP）位点的基因分型。邻接树（Neighbor-joining tree）与主成分分析（PCA）结果显示，堪萨斯与伊利诺伊生态型间存在显著遗传分化，且该分化更易通过环境隔离（IBE）而非距离隔离（IBD）进行解释。研究发现，种群内遗传变异占比达80%；令人意外的是，即使是生境破碎化的伊利诺伊草原，其种群内遗传多样性仍高达92%。通过Bayenv2软件分析，本研究鉴定出14个在生态型间排名靠前的受选择异常位点，这些位点与温度、降水气候变量显著相关；7个经BayeScan检测的FST异常位点中，有6个与Bayenv2鉴定的异常位点重合。较高的遗传多样性或有助于大须芒草种群更好地应对气候变化；但种群分化现象也提示，在草原修复工作中应优先选用当地生态型。对这一生态优势草本物种及其他草原物种的遗传变异的研究，将为理解气候变化背景下草原的响应机制与修复面临的挑战提供关键依据。