G3 (Bethesda). 2011 Oct;1(5):387-400. doi: 10.1534/g3.111.000539. Epub 2011 Oct 1.
We investigated species divergence, present and past gene flow, levels of nucleotide polymorphism, and linkage disequilibrium in two willows from the plant genus Salix. Salix belongs together with Populus to the Salicaceae family; however, most population genetic studies of Salicaceae have been performed in Populus, the model genus in forest biology. Here we present a study on two closely related willow species Salix viminalis and S. schwerinii, in which we have resequenced 33 and 32 nuclear gene segments representing parts of 18 nuclear loci in 24 individuals for each species. We used coalescent simulations and estimated the split time to around 600,000 years ago and found that there is currently limited gene flow between the species. Mean intronic nucleotide diversity across gene segments was slightly higher in S. schwerinii (π(i) = 0.00849) than in S. viminalis (π(i) = 0.00655). Compared with other angiosperm trees, the two willows harbor intermediate levels of silent polymorphisms. The decay of linkage disequilibrium was slower in S. viminalis compared with S. schwerinii, and we speculate that this is due to different demographic histories as S. viminalis has been partly domesticated in Europe.
我们研究了两个来自杨柳科的植物属柳属的物种分化、现在和过去的基因流、核苷酸多态性水平和连锁不平衡。柳属与杨属一起属于杨柳科；然而，杨柳科的大多数种群遗传研究都是在杨属中进行的，杨属是森林生物学的模式属。在这里，我们对两个密切相关的柳树种柳属和柳属进行了研究，我们对每个物种的 24 个个体中的 33 和 32 个核基因片段进行了重测序，这些片段代表了 18 个核基因座的部分。我们使用了合并模拟并估计了分裂时间大约在 60 万年前，并且发现目前这两个物种之间的基因流有限。跨基因片段的平均内含子核苷酸多样性在柳属中稍高（π(i) = 0.00849），而在柳属中较低（π(i) = 0.00655）。与其他被子植物树相比，这两个柳树种具有中等水平的沉默多态性。与柳属相比，柳属的连锁不平衡衰减较慢，我们推测这是由于不同的种群历史，因为柳属在欧洲部分被驯化。
