Data from: High levels of effective long-distance dispersal may blur ecotypic divergence in a rare terrestrial orchid

Background: Gene flow and adaptive divergence are key aspects of metapopulation dynamics and ecological speciation. Long-distance dispersal is hard to detect and few studies estimate dispersal in combination with adaptive divergence. The aim of this study was to investigate effective long-distance dispersal and adaptive divergence in the fen orchid (Liparis loeselii (L.) Rich.). We used amplified fragment length polymorphism (AFLP)-based assignment tests to quantify effective long-distance dispersal at two different regions in Northwest Europe. In addition, genomic divergence between fen orchid populations occupying two distinguishable habitats, wet dune slacks and alkaline fens, was investigated by a genome scan approach at different spatial scales (continental, landscape and regional) and based on 451 AFLP loci. Results: We expected that different habitats would contribute to strong divergence and restricted gene flow resulting in isolation-by-adaptation. Instead, we found remarkably high levels of effective long-distance seed dispersal and low levels of adaptive divergence. At least 15% of the assigned individuals likely originated from among-population dispersal events with dispersal distances up to 220 km. Six (1.3%) ‘outlier’ loci, potentially reflecting local adaptation to habitat-type, were identified with high statistical support. Of these, only one (0.22%) was a replicated outlier in multiple independent dune-fen population comparisons and thus possibly reflecting truly parallel divergence. Signals of adaptation in response to habitat type were most evident at the scale of individual populations. Conclusions: The findings of this study suggest that the homogenizing effect of effective long-distance seed dispersal may overwhelm divergent selection associated to habitat type in fen orchids in Northwest Europe.

背景：基因流与适应性分化是集合种群动态与生态物种形成的核心环节。长距离扩散难以被观测，同时结合适应性分化开展扩散评估的研究较为匮乏。本研究以沼兰（Liparis loeselii (L.) Rich.）为研究对象，旨在探究其有效长距离扩散与适应性分化情况。我们采用基于扩增片段长度多态性（amplified fragment length polymorphism, AFLP）的归属检验方法，对欧洲西北部两个不同区域的有效长距离扩散水平进行量化。此外，本研究通过不同空间尺度（大陆、景观及区域尺度）的基因组扫描方法，基于451个AFLP位点，对栖息于两种可区分生境——沙丘湿洼与碱性沼泽——的沼兰种群间的基因组分化展开分析。
结果：我们曾推测不同生境将驱动强烈的种群分化与受限的基因流，进而形成适应性隔离。但本研究却观测到极高水平的有效长距离种子扩散，以及较低程度的适应性分化。至少15%的归属个体可能来自种群间扩散事件，最大扩散距离可达220 km。本研究共鉴定出6个（占比1.3%）潜在反映生境类型局部适应的离群位点，且该结果具有较高统计学支持度。其中仅1个（占比0.22%）在多组独立的沙丘湿洼-碱性沼泽种群对比中均被鉴定为离群位点，因此该位点可能真正反映了平行分化。针对生境类型的适应性信号在单个种群尺度上最为显著。
结论：本研究结果表明，在欧洲西北部的沼兰种群中，有效长距离种子扩散所带来的均质化效应，可能超过了与生境类型相关的分化选择作用。