Data from: Surviving in mountain climate refugia: new insights from the genetic diversity and structure of the relict shrub Myrtus nivellei (Myrtaceae) in the Sahara desert

The identification of past glacial refugia has become a key topic for conservation under environmental change, since they contribute importantly to shaping current patterns of biodiversity. However, little attention has been paid so far to interglacial refugia despite their key role for the survival of relict species currently occurring in climate refugia. Here, we focus on the genetic consequences of range contraction on the relict populations of the evergreen shrub Myrtus nivellei, endemic in the Saharan mountains since at least the end of the last Green Sahara period, around 5.5 ka B.P. Multilocus genotypes (nuclear microsatellites and AFLP) were obtained from 215 individuals collected from 23 wadis (temporary rivers) in the three main mountain ranges in southern Algeria (the Hoggar, Tassili n’Ajjer and Tassili n’Immidir ranges). Identical genotypes were found in several plants growing far apart within the same wadis, a pattern taken as evidence of clonality. Multivariate analyses and Bayesian clustering revealed that genetic diversity was mainly structured among the mountain ranges, while low isolation by distance was observed within each mountain range. The range contraction induced by the last episode of aridification has likely increased the genetic isolation of the populations of M. nivellei, without greatly affecting the genetic diversity of the species as a whole. The pattern of genetic diversity observed here suggests that high connectivity may have prevailed during humid periods, which is consistent with recent paleoenvironmental reconstructions.

对冰期避难所（glacial refugia）的识别已成为环境变化下生物多样性保护研究的核心议题，因其对塑造当前生物多样性分布格局具有重要作用。然而，尽管间冰期避难所（interglacial refugia）对现存于气候避难所中的孑遗物种的存续至关重要，但迄今相关研究却鲜有关注。本研究聚焦于分布范围收缩对常绿灌木桃金娘（Myrtus nivellei）孑遗种群的遗传效应，该物种至少自末次绿色撒哈拉时期结束、约距今5500年（5.5 ka B.P.）以来便特有分布于撒哈拉山地。研究人员从阿尔及利亚南部三大主要山地（霍加尔山脉、塔西利-恩-阿耶山脉与塔西利-恩-伊姆迪尔山脉）的23条干谷（wadis，临时河道）中采集了215份个体样本，获取了多位点基因型数据（核微卫星（nuclear microsatellites）与AFLP）。在同一条干谷内相距较远的多株植物中发现了完全一致的基因型，这一模式被视为无性繁殖（clonality）的证据。多元分析与贝叶斯聚类（Bayesian clustering）结果显示，该物种的遗传多样性主要以山地为单元进行分化，而各山地内部的距离隔离效应较弱。末次干旱化事件引发的分布范围收缩，可能加剧了桃金娘（M. nivellei）种群间的遗传隔离，但并未对该物种种群整体的遗传多样性造成显著影响。本研究观测到的遗传多样性模式表明，在湿润时期该物种的种群间可能存在较高的连通性，这与近期的古环境重建结果相一致。