Data from: Demographic history of the trace metal hyperaccumulator Noccaea caerulescens (J. Presl and C. Presl) F. K. Mey. in Western Europe

Noccaea caerulescens (Brassicaceae) is a major pseudometallophyte model for the investigation of the genetics and evolution of metal hyperaccumulation in plants. We studied the population genetics and demographic history of this species to advance the understanding of among-population differences in metal hyperaccumulation and tolerance abilities. Sampling of seven to 30 plants was carried out in 62 sites in Western Europe. Genotyping was carried out using a combination of new chloroplast and nuclear neutral markers. A strong genetic structure was detected, allowing the definition of three genetic subunits. Subunits showed a good geographic coherence. Accordingly, distant metallicolous populations generally belonged to distinct subunits. Approximate Bayesian computation analysis of demographic scenarios among subunits further supported a primary isolation of populations from the southern Massif Central prior to last glacial maximum, whereas northern populations may have derived during postglacial recolonization events. Estimated divergence times among subunits were rather recent in comparison with the species history, but certainly before the establishment of anthropogenic metalliferous sites. Our results suggest that the large-scale genetic structure of N. caerulescens populations pre-existed to the local adaptation to metalliferous sites. The population structure of quantitative variation for metal-related adaptive traits must have established independently in isolated gene pools. However, features of the most divergent genetic unit (e.g. extreme levels of Cd accumulation observed in previous studies) question the putative relationships between adaptive evolution of metal-related traits and subunits isolation. Finally, admixture signals among distant metallicolous populations suggest a putative role of human activities in facilitating long-distance genetic exchanges.

天蓝遏蓝菜（Noccaea caerulescens，十字花科Brassicaceae）是研究植物金属超富集性状遗传学与演化机制的核心伪金属植物（pseudometallophyte）模式物种。本研究针对该物种开展种群遗传学与种群历史动态分析，旨在深化对不同种群间金属超富集与耐受能力差异的认知。研究团队在西欧62个采样点开展采样，每个位点采集7至30株个体。采用新型叶绿体与核基因组中性标记组合完成基因分型。研究检测到显著的种群遗传结构，可将其划分为3个遗传亚组，各亚组具有良好的地理分布一致性。据此，分布相隔较远的嗜金属种群通常隶属于不同的遗传亚组。通过近似贝叶斯计算（Approximate Bayesian Computation, ABC）对各亚组间的种群历史场景开展分析，结果进一步支持：源自南部中央地块（Massif Central）的种群早在末次盛冰期（Last Glacial Maximum, LGM）前就已发生初始隔离，而北部种群则可能是在冰期后种群重新定植过程中分化形成的。相较于该物种的整体演化历史，各遗传亚组间的估计分化时间相对较近，但无疑早于人为活动形成的金属污染生境。本研究结果表明，天蓝遏蓝菜种群的大尺度遗传结构，早于其对金属污染生境的局部适应过程而形成。与金属相关的适应性性状的数量变异种群结构，必然是在隔离的基因库中独立构建的。然而，分化程度最高的遗传亚组所具备的特征（例如既往研究中观测到的极高镉（Cadmium, Cd）积累水平），对金属相关性状的适应性演化与亚组隔离之间的推定关联提出了质疑。最后，异地嗜金属种群间检测到的基因混合信号，表明人类活动可能在促进远距离遗传交流方面发挥了推定的作用。