Reconstructing the early history of species divergence and quantifying the level of standing genetic variation in diverging populations are central to our understanding of ecotype formation and ultimately speciation. In this study, we used single nucleotide polymorphisms to reconstruct the evolutionary history of species divergence in coastal dune populations of the widespread terrestrial orchid Epipactis helleborine and to investigate the level of standing genetic variation in 29 coastal dune populations in a fragmented dune landscape along the Belgian and French coast. Additionally, we used seed introduction experiments to assess the potential for gene flow into existing populations after long-distance seed dispersal and the ability to colonize vacant sites. Our results showed that coastal dune populations diverged only recently from inland populations, went through a significant bottleneck and were most probably the result of a single colonization event. Current levels of population genetic diversity are low and not related to population size or spatial isolation. The sampled dune populations also showed little genetic differentiation, and no apparent spatial genetic structure was observed. Seed introduction experiments showed that seeds of coastal dune populations germinated easily in both occupied and unoccupied sites in dune habitat, indicating that the availability of suitable mycorrhizal fungi is not limiting the distribution of coastal dune populations and that gene flow through seeds has probably contributed to the observed low levels of genetic differentiation. Overall, these results are consistent with a process of genetic divergence after a single, recent colonization event, followed by extensive gene flow among populations.

中文翻译：

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陆地陆生兰花Epipactis helleborine沿海沙丘种群的遗传多样性和变异性低

重建物种差异的早期历史并量化差异种群中遗传变异的水平对我们理解生态型形成和最终物种形成至关重要。在这项研究中，我们使用单核苷酸多态性重建了广泛的陆地兰花Epipactis helleborine的沿海沙丘种群中物种差异的进化历史。并研究比利时和法国沿岸沙丘景观零碎的29个沿海沙丘种群的常规遗传变异水平。另外，我们使用种子引入实验评估了长距离种子扩散后基因流向现有种群的潜力以及在空位上定殖的能力。我们的结果表明，沿海沙丘种群只是最近才与内陆种群分化，经历了严重的瓶颈，很可能是一次殖民化事件的结果。当前的种群遗传多样性水平很低，与种群规模或空间隔离无关。采样的沙丘种群也几乎没有遗传分化，也没有观察到明显的空间遗传结构。种子导入实验表明，沿海沙丘种群的种子容易在沙丘栖息地的有人居住和未有人居住的地方发芽，这表明合适的菌根真菌的可用性并不限制沿海沙丘种群的分布，而通过种子的基因流可能有助于观察到低水平的遗传分化。总的来说，这些结果与最近一次定居事件发生后，随后种群之间大量基因流动的遗传分化过程一致。这表明合适的菌根真菌的可用性并不限制沿海沙丘种群的分布，并且通过种子的基因流可能导致观察到的低水平的遗传分化。总的来说，这些结果与最近一次定居事件发生后，随后种群之间大量基因流动的遗传分化过程一致。这表明合适的菌根真菌的可用性并不限制沿海沙丘种群的分布，并且通过种子的基因流可能导致观察到的低水平的遗传分化。总的来说，这些结果与最近一次定居事件发生后，随后种群之间大量基因流动的遗传分化过程一致。