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.

在全球环境不断变化的背景下，位于物种分布区后缘（rear-edge）的种群，其在生物多样性保护中所具备的生态与进化重要性往往不成比例地突出。然而，针对此类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的进化历史；该树种作为河岸生态系统的关键物种，发挥着不可或缺的生态功能。我们对分布于北非的19个种群共551株成年个体，在12个微卫星位点（microsatellite loci）上完成了基因分型，并采用基于溯祖模拟的方法，重构了这些种群的种群统计历史与进化历程。令人意外的是，摩洛哥的欧洲桤木为四倍体，这充分彰显了该种群在该物种（通常为二倍体）中的极强独特性。最优拟合的种群历史重构模型显示，摩洛哥种群具有孑遗属性：它们成功经受住了过往的气候变化事件，且其起源远早于阿尔及利亚与突尼斯的种群。本研究揭示了分布区后缘种群可能拥有的复杂种群历史——本次研究的后缘种群既包含古老且气候稳定的孑遗类群，也包含更为年轻的种群，其遗传多样性在定量与定性层面均表现出显著差异。针对地中海地区正在发生的气候变化，本研究强调了作为河岸生态系统关键物种的分布区后缘边缘种群，其极高的进化与保护价值。