Data from: Patterns of genetic diversity reveal multiple introductions and recurrent founder effects during range expansion in invasive populations of Geranium carolinianum (Geraniaceae)

Genetic diversity, and thus the adaptive potential of invasive populations, is largely based on three factors: patterns of genetic diversity in the species' native range, the number and location of introductions, and the number of founding individuals per introduction. Specifically, reductions in genetic diversity ("founder effects") should be stronger for species with low within-population diversity in their native range and few introductions of few individuals to the invasive range. We test these predictions with Geranium carolinianum, a winter annual herb native to North America and invasive in China. We measure the extent of founder effects using allozymes and microsatellites, and ask whether this is consistent with its colonization history and patterns of diversity in the native range. In the native range, genetic diversity is higher and structure is lower than expected based on life-history traits. In China, our results provide evidence for multiple introductions near Nanjing, Jiangsu province, with subsequent range expansion to the west and south. Patterns of genetic diversity across China reveal weak founder effects that are driven largely by low- diversity populations at the expansion front, away from the introduction location. This suggests that reduced diversity in China has resulted from successive founder events during range expansion, and that the loss of genetic diversity in the Nanjing area was mitigated by multiple introductions from diverse source populations. This has implications for the future of G. carolinianum in China, as continued gene flow among populations should eventually increase genetic diversity within the more recently founded populations.入侵种群的遗传多样性及其适应性潜力，主要取决于三大核心因素：该物种原生分布区的遗传多样性格局、引种次数与引种位点，以及每次引种的奠基个体数量。具体而言，若某物种在原生分布区内的种群内遗传多样性较低，且向入侵区的引种次数少、单次引种个体数量不足，则其遗传多样性降低（即奠基者效应（founder effects））的程度会更为显著。本研究以北美原生、中国入侵的冬性一年生草本植物卡罗琳老鹳草（Geranium carolinianum）为研究对象，对上述预测进行验证。研究采用同工酶（allozymes）与微卫星（microsatellites）两种分子标记量化奠基者效应的强度，并探讨其是否符合该物种的定殖历史与原生分布区的多样性格局。在原生分布区内，该物种的遗传多样性高于基于生活史特征的预期值，而遗传结构则低于预期。针对中国入侵区的分析结果显示，该物种最初在江苏省南京周边存在多次引种事件，随后向西、向南实现了范围扩张。中国全境的遗传多样性格局显示，奠基者效应整体较弱，这种弱效应主要源于远离引种位点的扩张前沿区域存在低多样性种群。这表明中国入侵种群的多样性降低，是由范围扩张过程中接连发生的奠基事件所致；而南京地区的遗传多样性流失之所以得到缓解，是因为多次引种来自多个遗传多样的源种群。该研究结果对卡罗琳老鹳草在中国的未来种群动态具有重要启示：种群间持续的基因流最终将提升新近建立种群的遗传多样性水平。