Data from: Molecular divergence in tropical tree populations occupying environmental mosaics

Unveiling the genetic basis of local adaptation to environmental variation is a major goal in molecular ecology. In rugged landscapes characterised by environmental mosaics, living populations and communities can experience steep ecological gradients over very short geographical distances. In lowland tropical forests, interspecific divergence in edaphic specialization (for seasonally flooded bottomlands and seasonally dry terra firme soils) has been proven by ecological studies on adaptive traits. Some species are nevertheless capable of covering the entire span of the gradient; intraspecific variation for adaptation to contrasting conditions may explain the distribution of such ecological generalists. We investigated whether local divergence happens at small spatial scales in two stands of Eperua falcata (Fabaceae), a widespread tree species of the Guiana Shield. We investigated SNP and sequence divergence as well as spatial genetic structure (SGS) at four genes putatively involved in stress response and three genes with unknown function. Significant genetic differentiation was observed among sub-populations within stands, and eight SNP loci showed patterns compatible with disruptive selection. SGS analysis showed genetic turnover along the gradients at three loci, and at least one haplotype was found to be in repulsion with one habitat. Taken together, these results suggest genetic differentiation at small spatial scale in spite of gene flow. We hypothesize that heterogeneous environments may cause molecular divergence, possibly associated to local adaptation in E. falcata.揭示适应环境变异的局部适应的遗传基础，是分子生态学（molecular ecology）领域的一项核心研究目标。在以环境镶嵌为特征的崎岖地貌中，存活的种群与群落可在极短的地理距离内遭遇剧烈的生态梯度。在低地热带森林中，针对土壤生境特化的种间分化（如季节性泛滥的河漫滩与季节性干旱的terra firme陆地土壤），已通过适应性性状的生态学研究得到验证。然而部分物种能够覆盖该梯度的全部区间；针对极端环境的种内适应变异，或可解释这类生态广适物种的分布格局。我们以圭亚那盾地（Guiana Shield）广布的乔木树种Eperua falcata（豆科Fabaceae）的两个林分作为研究对象，探究其是否在小空间尺度上发生局部分化。我们对4个推测参与胁迫响应的基因以及3个功能未知的基因，开展了单核苷酸多态性（SNP）与序列分化分析，同时探究了空间遗传结构（Spatial Genetic Structure, SGS）。研究在林分内的亚种群间观测到了显著的遗传分化，且有8个SNP位点呈现出与歧化选择相符的演化模式。空间遗传结构分析显示，3个位点的遗传组成沿梯度发生更替，且至少有一个单倍型与某一栖息地呈现排斥关联。综合上述结果，即便存在基因流，该物种仍在小空间尺度上呈现出遗传分化。我们提出假说：异质环境可能引发分子分化，这一过程或与E. falcata的局部适应相关。