Adaptation across geographic ranges is consistent with strong selection in marginal climates and legacies of range expansion

AbstractEvery species experiences limits to its geographic distribution. Some evolutionary models predict that populations at range edges are less well-adapted to their local environments due to drift, expansion load, or swamping gene flow from the range interior. Alternatively, populations near range edges might be uniquely adapted to marginal environments. In this study, we use a database of transplant studies that quantify performance at broad geographic scales to test how local adaptation, site quality, and population quality change from spatial and climatic range centers towards edges. We find that populations from poleward edges perform relatively poorly, both on average across sites (15% lower population quality) and when compared to other populations at home (31% relative fitness disadvantage), consistent with these populations harboring high genetic load. Populations from equatorial edges also perform poorly on average (18% lower population quality) but, in contrast, outperform foreign populations (16% relative fitness advantage), suggesting that populations from equatorial edges have adapted to unique environments. Finally, we find that populations from sites that are thermally extreme relative to the species' niche demonstrate strong local adaptation, regardless of geographic position. Our findings indicate that both nonadaptive processes and adaptive evolution contribute to variation in adaptation across species' ranges., MethodsThis dataset contains fitness data gathered from a systematic literature search of transplant experiments, along with geographic and climatic covariates derived for this study. Included is the final data file and model running scripts, as well as scripts, GBIF occurrence data, and intermediate files demonstrating how spatial and climatic predictors were calculated., Usage notesSee README file.

**摘要**：每个物种的地理分布均存在边界限制。部分演化模型预测，由于遗传漂变、扩张负荷或来自分布区内部的基因流淹没效应，分布区边缘的种群对本地环境的适应性往往更差；而另一种演化假说则认为，分布区边缘的种群可能已特化适应了边缘生境。本研究依托一套量化了大地理尺度下物种适合度的移植实验数据库，检验本地适应性、生境质量与种群质量如何从物种的空间和气候分布中心向边缘发生变化。研究发现，来自极向边缘的种群整体表现较差：在所有移植生境中的平均种群质量降低15%，且相较于本土种群的相对适合度低31%，这与这类种群携带较高遗传负荷的结论一致。来自赤道边缘的种群平均表现同样较差（种群质量降低18%），但与之相反的是，其适合度高于外来种群（相对适合度优势达16%），这表明赤道边缘种群已适应了独特的生境环境。最后，本研究发现，相较于物种生态位内热环境极端的位点的种群，无论其地理位置如何，均表现出极强的本地适应性。本研究结果表明，非适应性演化过程与适应性进化共同塑造了物种分布范围内适应性的差异。**方法**：本数据集涵盖通过系统文献检索获取的移植实验适合度数据，以及为本研究提取的地理与气候协变量。数据集包含最终数据文件、模型运行脚本，以及用于计算空间与气候预测因子的脚本、GBIF（Global Biodiversity Information Facility，全球生物多样性信息设施）物种出现记录数据与展示预测因子计算过程的中间文件。**使用说明**：详见README文件。