Data from: Spatial genetic structure in Beta vulgaris subsp. maritima and Beta macrocarpa reveals the effect of contrasting mating system, influence of marine currents and footprints of postglacial recolonisation routes

Understanding the factors that contribute to population genetic divergence across a species' range is a long-standing goal in evolutionary biology and ecological genetics. We examined the relative importance of historical and ecological features in shaping the present-day spatial patterns of genetic structure in two related plant species, Beta vulgaris subsp. maritima and Beta macrocarpa. Using nuclear and mitochondrial markers, we surveyed 93 populations from Brittany (France) to Morocco – the southern limit of their species' range distribution. Whereas B. macrocarpa showed a genotypic structure and a high level of genetic differentiation indicative of selfing, the population genetic structure of B. vulgaris subsp. maritima was consistent with an outcrossing mating system. We further showed (1) a strong geographic clustering in coastal B. vulgaris subsp. maritima populations that highlighted the influence of marine currents in shaping different lineages and (2) a peculiar genetic structure of inland B. vulgaris subsp. maritima populations that could indicate the admixture of distinct evolutionary lineages and recent expansions associated with anthropogenic disturbances. Spatial patterns of nuclear diversity and differentiation also supported a stepwise recolonization of Europe from Atlantic-Mediterranean refugia after the last glacial period, with leading-edge expansions. However, cytoplasmic diversity was not impacted by postglacial recolonization: stochastic long-distance seed dispersal mediated by major oceanic currents may mitigate the common patterns of reduced cytoplasmic diversity observed for edge populations. Overall, the patterns we documented here challenge the general view of reduced genetic diversity at the edge of a species' range distribution and provide clues for understanding how life-history and major geographic features interact to shape the distribution of genetic diversity.

阐明物种分布范围内种群遗传分化的影响因素，是进化生物学与生态遗传学领域长期以来的核心研究目标之一。本研究针对两个近缘植物类群：海滨甜菜（Beta vulgaris subsp. maritima）与大果甜菜（Beta macrocarpa），探究了历史与生态特征对其现今遗传结构空间格局的塑造作用，并比较了二者的相对重要性。本研究利用核基因与线粒体分子标记，对从法国布列塔尼至摩洛哥（该类群分布范围南界）的93个种群开展了遗传采样与分析。大果甜菜表现出与自交繁殖相符的基因型结构与高水平遗传分化，而海滨甜菜的种群遗传结构则符合异交繁育系统的特征。本研究进一步发现：其一，海滨甜菜沿海种群呈现显著的地理聚类特征，揭示了海流对不同演化支系的塑造作用；其二，海滨甜菜内陆种群具有特殊的遗传结构，这可能暗示其源自不同演化支系的遗传混合，以及受人为干扰驱动的近期种群扩张事件。核基因多样性与分化的空间格局同样支持：末次冰期结束后，欧洲种群从大西洋-地中海避难所逐步回迁，并伴随边缘种群扩张。但细胞质多样性并未受冰期后回迁过程的影响：由主要海流介导的随机性长距离种子传播，或许能够缓解边缘种群普遍存在的细胞质多样性降低现象。总体而言，本研究记录的遗传格局挑战了“物种分布边缘种群遗传多样性降低”的主流观点，并为解析生活史特征与关键地理要素如何共同塑造遗传多样性分布格局提供了新的线索。