Data from: The influence of landscape, climate, and history on spatial genetic patterns in keystone plants (Azorella) on sub-Antarctic islands

The distribution of genetic variation in species is governed by factors that act differently across spatial scales. To tease apart the contribution of different processes, especially at intermediate spatial scales, it is useful to study simpler ecosystems such as those on sub-Antarctic oceanic islands. In this study, we characterize spatial genetic patterns of two keystone plant species, Azorella selago on sub-Antarctic Marion Island and Azorella macquariensis on sub-Antarctic Macquarie Island. Although both islands experience a similar climate and vegetation structure, they differ significantly in topography and geological history. We genotyped six microsatellites for 1149 individuals from 123 sites across Marion Island and 372 individuals from 42 sites across Macquarie Island. We tested for spatial patterns in genetic diversity, including correlation with elevation and vegetation type, and clines in different directional bearings. We also examined genetic differentiation within islands, isolation-by-distance with and without accounting for direction, and signals of demographic change. Marion Island was found to have a distinct northwest-southeast divide, with lower genetic diversity and more sites with signal of population expansion in the northwest. We attribute this to asymmetric seed dispersal by the dominant northwesterly winds, and to population persistence in a southwestern refugium during the last Glacial Maximum. No apparent spatial pattern, but greater genetic diversity and differentiation between sites, was found on Macquarie Island, which may be due to the narrow length of the island in the direction of the dominant winds and longer population persistence permitted by the lack of extensive glaciation on the island.物种遗传变异的分布受在不同空间尺度上作用方式各异的因子调控。为厘清不同过程的贡献，尤其是在中等空间尺度下，研究诸如亚南极远洋岛屿生态系统这类相对简单的生态系统颇具价值。本研究对两种关键植物种（keystone plant species）的空间遗传格局进行了表征：分别为亚南极马里恩岛的Azorella selago以及亚南极麦夸里岛的Azorella macquariensis。尽管两座岛屿的气候与植被结构相近，但在地形与地质历史上存在显著差异。我们对马里恩岛123个样点的1149个个体、麦夸里岛42个样点的372个个体开展了6个微卫星（microsatellites）位点的基因分型。我们检测了遗传多样性的空间格局，包括其与海拔、植被类型的相关性，以及不同方位的遗传梯度；同时还分析了岛内遗传分化、考虑与不考虑方位的距离衰减隔离效应（isolation-by-distance），以及种群动态变化的信号。研究发现，马里恩岛存在清晰的西北-东南分化格局，西北部遗传多样性更低，且更多样点呈现种群扩张的信号，我们将其归因于优势西北风介导的不对称种子扩散，以及末次冰盛期西南避难所的种群留存。麦夸里岛未显现明显空间格局，但样点间的遗传多样性与分化程度更高，这或源于该岛在优势风向方向上的跨度较窄，且岛内未经历大规模冰川作用，使得种群得以长期存续。