Department of Biology, Plant Conservation and Population Biology, Katholieke Universiteit Leuven, Leuven, Belgium.
Research Institute for Forest and Nature, Geraardsbergen, Belgium.
Ann Bot. 2023 Apr 28;131(4):623-634. doi: 10.1093/aob/mcad010.
Historical changes in environmental conditions and colonization-extinction dynamics have a direct impact on the genetic structure of plant populations. However, understanding how past environmental conditions influenced the evolution of species with high gene flow is challenging when signals for genetic isolation and adaptation are swamped by gene flow. We investigated the spatial distribution and genetic structure of the widespread terrestrial orchid Epipactis helleborine to identify glacial refugia, characterize postglacial population dynamics and assess its adaptive potential.
Ecological niche modelling was used to locate possible glacial refugia and postglacial recolonization opportunities of E. helleborine. A large single-nucleotide polymorphism (SNP) dataset obtained through genotyping by sequencing was used to define population genetic diversity and structure and to identify sources of postglacial gene flow. Outlier analyses were used to elucidate how adaptation to the local environment contributed to population divergence.
The distribution of climatically suitable areas was restricted during the Last Glacial Maximum to the Mediterranean, south-western Europe and small areas in the Alps and Carpathians. Within-population genetic diversity was high in E. helleborine (mean expected heterozygosity, 0.373 ± 0.006; observed heterozygosity, 0.571 ± 0.012; allelic richness, 1.387 ± 0.007). Italy and central Europe are likely to have acted as important genetic sources during postglacial recolonization. Adaptive SNPs were associated with temperature, elevation and precipitation.
Forests in the Mediterranean and Carpathians are likely to have acted as glacial refugia for Epipactis helleborine. Postglacial migration northwards and to higher elevations resulted in the dispersal and diversification of E. helleborine in central Europe and Italy, and to geographical isolation and divergent adaptation in Greek and Italian populations. Distinguishing adaptive from neutral genetic diversity allowed us to conclude that E. helleborine has a high adaptive potential to climate change and demonstrates that signals of adaptation and historical isolation can be identified even in species with high gene flow.
环境条件的历史变化和定居-灭绝动态对植物种群的遗传结构有着直接的影响。然而，当遗传隔离和适应的信号被基因流淹没时，理解过去的环境条件如何影响具有高基因流的物种的进化是具有挑战性的。我们研究了广泛分布的陆生兰花拟兰属 helleborine 的空间分布和遗传结构，以确定冰川避难所，描述冰川后种群动态，并评估其适应潜力。
通过生态位模型来确定拟兰属 helleborine 的可能冰川避难所和冰川后再定居机会。通过测序的基因分型获得的大型单核苷酸多态性 (SNP) 数据集用于定义种群遗传多样性和结构，并识别冰川后基因流的来源。通过选择分析来阐明对当地环境的适应如何促进种群分歧。
在末次冰期最大期，气候适宜区的分布受到限制，仅限于地中海、西南欧以及阿尔卑斯山和喀尔巴阡山脉的小区域。拟兰 helleborine 内的种群遗传多样性较高（平均期望杂合度为 0.373 ± 0.006；观察杂合度为 0.571 ± 0.012；等位基因丰富度为 1.387 ± 0.007）。意大利和中欧可能在冰川后再定居期间充当了重要的遗传来源。适应性 SNP 与温度、海拔和降水有关。
地中海和喀尔巴阡山脉的森林可能是拟兰属 helleborine 的冰川避难所。冰川后向北和向高海拔地区的迁移导致 helleborine 在中欧和意大利的扩散和多样化，以及在希腊和意大利种群中的地理隔离和趋异适应。区分适应性和中性遗传多样性使我们能够得出结论，拟兰属 helleborine 对气候变化具有很高的适应潜力，并表明即使在具有高基因流的物种中，也可以识别适应和历史隔离的信号。
