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.

天蓝菥蓂（Noccaea caerulescens，十字花科Brassicaceae）是研究植物金属超富集现象的遗传学与演化机制的核心伪金属植物（pseudometallophyte）模式物种。本研究针对该物种的群体遗传学与种群历史展开分析，旨在深化对不同种群间金属超富集能力与耐受能力差异的认知。研究团队于西欧62个采样位点开展采样，每个位点采集7至30株个体。研究结合全新的叶绿体与核中性标记基因完成基因分型。本研究检测到强烈的遗传结构，据此可将该物种划分为3个遗传亚组。各遗传亚组呈现出良好的地理关联性。据此，异地的富金属生境种群通常隶属于不同的遗传亚组。针对各遗传亚组间种群历史情景的近似贝叶斯计算（Approximate Bayesian Computation）分析进一步证实，源自法国中央高原（Massif Central）南部的种群早在末次冰盛期（Last Glacial Maximum）前便已发生初步隔离；而北部种群则可能形成于冰期后的再定植过程中。相较于该物种的整体演化历史，各遗传亚组间的分化时间相对较近，但必然早于人为金属污染生境的形成时期。本研究结果显示，天蓝菥蓂种群的大范围遗传结构，在其对富金属生境产生本地适应之前便已存在。与金属富集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演化形成的。但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端镉（Cd）富集水平），对金属相关适应性性状的演化与遗传亚组隔离之间的推定关联提出了质疑。最后，异地富金属生境种群间检测到的遗传混合信号表明，人类活动可能在促进远距离遗传交流中发挥了潜在作用。