Data from: High genetic diversity and distinctiveness of rear-edge climate relicts maintained by ancient tetraploidisation for Alnus glutinosa

Populations located at the rear-edge of a species’ distribution may have disproportionate ecological and evolutionary importance for biodiversity conservation in a changing global environment. Yet genetic studies of such populations remain rare. This study investigates the evolutionary history of North-African low latitude marginal populations of Alnus glutinosa Gaertn., a European tree species that plays a significant ecological role as a keystone of riparian ecosystems. We genotyped 551 adults from 19 populations located across North Africa at 12 microsatellite loci and applied a coalescent-based simulation approach to reconstruct the demographic and evolutionary history of these populations. Surprisingly, Moroccan trees were tetraploids demonstrating a strong distinctiveness of these populations within a species otherwise known as diploid. Best-fitting models of demographic reconstruction revealed the relict nature of Moroccan populations that were found to have withstood past climate change events and to be much older than Algerian and Tunisian populations. This study highlights the complex demographic history that can be encountered in rear-edge distribution margins that here consist of both old stable climate relict and more recent populations, distinctively diverse genetically both quantitatively and qualitatively. We emphasize the high evolutionary and conservation value of marginal rear-edge populations of a keystone riparian species in the context of on-going climate change in the Mediterranean region.

在全球环境持续变化的背景下，分布于物种分布区后缘的种群，往往对生物多样性保护具备远超其种群体量占比的重要生态与进化价值。然而，针对这类边缘种群的遗传学研究仍较为匮乏。本研究聚焦于欧洲树种欧洲桤木（Alnus glutinosa Gaertn.）的北非低纬度边缘种群，该树种作为河岸生态系统的关键物种，发挥着举足轻重的生态功能。我们对横跨北非的19个种群共551株成年个体进行了12个微卫星位点（microsatellite loci）的基因分型，并采用基于溯祖模拟的方法，重建了这些种群的种群历史与进化历程。令人意外的是，摩洛哥的欧洲桤木为四倍体，这凸显出该种群在以二倍体为主的该物种中极强的独特性。最优拟合的种群历史重建模型显示，摩洛哥种群属于孑遗种群，它们能够抵御过往的气候变化事件，且其起源远早于阿尔及利亚和突尼斯的种群。本研究揭示了分布区后缘种群可能拥有的复杂种群历史：本次研究涉及的后缘种群既包含古老稳定的气候孑遗类群，也涵盖较新建立的种群，其遗传多样性在定量与定性层面均呈现出显著差异。在地中海地区气候变化持续加剧的背景下，我们着重强调了这类河岸关键物种的后缘边缘种群所具备的极高进化与保护价值。