Fragmented landscapes may have implications for the genetic structure of populations and for the microevolution of plant species. In particular, landscape fragmentation and/or population isolation might affect the evolution of plant mating systems. Here, we study the consequences of landscape fragmentation on the genetic structure of populations of a perennial herb, Vincetoxicum hirundinaria with a mixed mating system. Our study area, the south‐western Finnish archipelago, was formed after the glacial ice sheet started to retreat 12 000 years ago. Due to the isostatic land uplift following the glacial retreat, suitable habitats have been formed gradually, and as a consequence, populations of V. hirundinaria differ in age, size and their degree of isolation in the area. We hypothesized that a mixed‐mating system has been selected for in these populations due to the advantage of self‐fertilization in newly colonized areas and the advantage of outcrossing in adaptation to heterogeneous environments. To test this hypothesis, we collected seeds of open‐pollinated flowers from 13 V. hirundinaria populations differing in size, age and isolation, and used 15 microsatellite markers to perform progeny‐array analysis to estimate population‐level outcrossing rates, population genetic indices and population structure. We found that V. hirundinaria is almost completely outcrossing in the study area with no signs of past self‐fertilization and/or mating among relatives. The overall low inbreeding coefficients indicate that even in small populations mating among relatives is rare. High allelic richness of both maternal and offspring genotypes as well as limited genetic differentiation among the studied populations indicate strong gene flow among them. Our findings suggest that V. hirundinaria has successful seed and pollen dispersal among populations that has allowed colonization of new habitats in this fragmented landscape and led to a genetically well‐mixed group of populations at the scale of the study.

中文翻译：

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强大的基因流动解释了多年生草本Vincetoxicum hirundinaria在零散的景观中缺乏交配系统变异

零散的景观可能会对种群的遗传结构和植物物种的微观进化产生影响。尤其是，景观破碎化和/或种群隔离可能会影响植物交配系统的进化。在这里，我们研究了景观破碎化对多年生草本植物Vincetoxicum hirundinaria具有混合交配系统的种群遗传结构的影响。我们的研究区域是西南芬兰群岛，是在12000年前冰川退缩之后形成的。由于冰川退缩后土地的等压上升，逐渐形成了合适的栖息地，因此，平底山弧菌种群该地区的年龄，大小及其隔离程度各不相同。我们假设在这些人群中选择了混合交配系统，这是由于在新殖民地地区自我施肥的优势以及异化适应异质环境的优势。为了验证该假设，我们从大小，年龄和分离度不同的13个hirundinaria种群中采集了开放授粉的花的种子，并使用15个微卫星标记进行后代阵列分析以估计种群水平的异交率，种群遗传指数和人口结构。我们发现V. hirundinaria在研究区域几乎完全异化，没有亲戚过去的自我受精和/或交配的迹象。总的近交系数低表明，即使在少数人群中，亲戚之间的交配也很少。母本和后代基因型的高度等位基因丰富性以及有限的遗传分化表明所研究的群体之间的基因流动性强。我们的发现表明，hirundinaria弧菌在种群之间成功地进行了种子和花粉扩散，从而使这个分散的景观中能够有新的栖息地定居，并在研究规模上导致了遗传上充分混合的种群。