Data from: The relevance of gene flow in metapopulation dynamics of an oceanic island endemic, Olea europaea subsp guanchica

Theoretical and empirical studies suggest that geographical isolation and extinction-recolonization dynamics are two factors causing strong genetic structure in metapopulations. Here, we investigated the effect of population age structure and isolation by distance in the patterns of genetic diversity in a tree species (Olea europaea subsp. guanchica) sporadically affected by volcanic events across the Canarian archipelago. Genetic variation was assessed at six nuclear microsatellites (nDNA) and six chloroplast fragments (cpDNA) in nine subpopulations sampled on four oceanic islands. Subpopulations occurring on more recent substrates were more differentiated than those on older substrates, but within-subpopulation genetic diversity was not significantly different between age groups for any type of marker. Contrary to the general trend for island systems, between-island differentiation was extremely low, and lower than differentiation between subpopulations on the same island. The pollen-to-seed ratio was close to one, two orders of magnitude lower than the average estimated for other wind-pollinated, animal-dispersed plants. Our results showed that population turnover and geographical isolation increased genetic differentiation relative to an island model at equilibrium, but overall genetic structure was unexpectedly weak for a species distributed among islands. This empirical study shows that extensive gene flow, particularly mediated by seeds, can ameliorate population subdivision resulting from extinction-recolonization dynamics and isolation by distance理论与实证研究均表明，地理隔离以及灭绝-重建动态（extinction-recolonization dynamics）是导致集合种群（metapopulations）形成强烈遗传结构的两大核心驱动因素。本研究以分布于加那利群岛（Canarian archipelago）、偶受火山活动影响的树种油橄榄（Olea europaea subsp. guanchica）为研究对象，探究种群年龄结构与距离隔离（isolation by distance）对其遗传多样性格局的影响。研究通过6个核微卫星（nuclear microsatellites，nDNA）位点与6个叶绿体片段（chloroplast fragments，cpDNA），对采自4个大洋岛屿的9个亚种群的遗传变异进行了评估。定植于较新近形成基质的亚种群，其遗传分化程度高于生长于较古老基质的亚种群；但无论采用何种分子标记类型，不同基质年龄组的亚种群内部遗传多样性均无显著差异。与岛屿系统的普遍演化趋势相悖，本研究中岛屿间的遗传分化程度极低，甚至低于同一岛屿内不同亚种群间的分化水平。花粉-种子传播比（pollen-to-seed ratio）接近1，较风媒传粉、动物介导种子传播的其他植物的平均估算值低两个数量级。本研究结果显示，相较于平衡岛屿模型（island model），种群周转（population turnover）与地理隔离会加剧遗传分化；但对于岛屿分布的物种而言，其整体遗传结构却弱得出人意料。本实证研究表明，广泛的基因流——尤其是以种子为媒介的基因流——能够缓解由灭绝-重建动态与距离隔离所引发的种群遗传分化。