Spatial and ecological population genetic structures within two island-endemic Aeonium species of different niche width

The Crassulacean genus Aeonium is a well-known example for plant species radiation on oceanic archipelagos. However, while allopatric speciation among islands is documented for this genus, the role of intra-island speciation due to population divergence by topographical isolation or ecological heterogeneity has not yet been addressed. The aim of this study was to investigate intraspecific genetic structures and to identify spatial and ecological drivers of genetic population differentiation on the island scale. We analyzed inter simple sequence repeat variation within two island-endemic Aeonium species of La Palma: one widespread generalist that covers a large variety of different habitat types (Ae. davidbramwellii) and one narrow ecological specialist (Ae. nobile), in order to assess evolutionary potentials on this island. Gene pool differentiation and genetic diversity patterns were associated with major landscape structures in both species, with phylogeographic implications. However, overall levels of genetic differentiation were low. For the generalist species, outlier loci detection and loci–environment correlation approaches indicated moderate signatures of divergent selection pressures linked to temperature and precipitation variables, while the specialist species missed such patterns. Our data point to incipient differentiation among populations, emphasizing that ecological heterogeneity and topographical structuring within the small scales of an island can foster evolutionary processes. Very likely, such processes have contributed to the radiation of Aeonium on the Canary Islands. There is also support for different evolutionary mechanisms between generalist and specialist species.景天科（Crassulaceae）莲花掌属（Aeonium）是海洋群岛植物物种辐射演化的经典研究范例。尽管该属的岛间异域成种（allopatric speciation）现象已有文献记载，但由地形隔离或生态异质性导致种群分化、进而引发岛内物种形成的作用机制，至今仍未得到充分探讨。本研究以拉帕尔马岛（La Palma）的两种莲花掌属岛生特有物种为研究对象，旨在探究其种内遗传结构，并明确岛屿尺度下遗传种群分化的空间与生态驱动因子。我们对这两个物种开展了简单序列重复区间扩增多态性（inter simple sequence repeat, ISSR）分析：其中一种为广适性泛生种，可适配多种生境类型（Ae. davidbramwellii），另一种为生态位狭窄的特化种（Ae. nobile），以此评估该岛的演化潜力。两种物种的基因库分化与遗传多样性模式均与区域主要地形结构显著相关，且具备系统地理学研究意义；但整体遗传分化水平较低。针对广适性物种，异常位点检测与位点-环境关联分析结果显示，其存在与温度、降水变量相关的中等强度歧化选择信号；而特化种未呈现此类模式。本研究数据表明种群间已出现初期分化，凸显了岛屿小尺度范围内的生态异质性与地形结构可推动演化进程。此类过程极有可能推动了莲花掌属在加那利群岛的物种辐射演化，同时也佐证了广适性与特化物种间存在差异化的演化机制。