Data from: Genetic admixing of two evergreen oaks, Quercus acuta and Q. sessilifolia (subgenus Cyclobalanopsis), is the result of interspecific introgressive hybridization

In forests worldwide, Quercus is a major genus; however, the boundaries between the constituent species are relatively weak, and hybridization is reported frequently. In this study, we examined Quercus acuta and Quercus sessilifolia (subgenus Cyclobalanopsis), which have a putative hybrid—Q. x takaoyamensis. We investigated leaf morphological traits and microsatellites of Q. acuta and Q. sessilifolia in the area where the two species are both found. Although the leaf traits overlapped, the two species could be distinguished morphologically as demonstrated by principal component analysis based on a range of these traits. They were also genetically differentiated, with F ST = 0.104. However, they shared most of the alleles at all eight loci examined, and considerable genetic admixing was detected. Admixture analysis demonstrated that Q. acuta and Q. sessilifolia, respectively, contained 11 and 24 % of individuals with a probability of less than 0.9 of being correctly assigned to their species. Model-based testing showed that this admixing was created by not only shared ancestral polymorphism but also by hybridization. Effective population size and migration rate were estimated using the coalescent approach. We estimated 8.843 and 71.98 effective numbers of migrants per generation to Q. acuta and Q. sessilifolia, respectively. Theoretically, one to ten migrants per generation are required to prevent complete genetic differentiation. Based on the results of this study, it appears that genetic admixing, with sharing of most alleles, is probably common in the two species and is maintained by interspecific introgressive hybridization.

全球森林中，栎属（Quercus）是优势属之一；但其组成物种间的分类界限相对模糊，且频繁有杂交现象被报道。本研究以青冈亚属（subgenus Cyclobalanopsis）下的赤皮青冈（Quercus acuta）与栎叶青冈（Quercus sessilifolia）为研究对象，二者存在推定杂交种——高野山栎（Q. x takaoyamensis）。我们在二者同域分布的区域，对赤皮青冈和栎叶青冈的叶片形态性状及微卫星（microsatellite）标记展开了分析。尽管二者的叶片性状存在重叠，但基于多组叶片性状的主成分分析（principal component analysis）结果显示，二者仍可通过形态特征加以区分。二者在遗传层面同样存在分化，遗传分化系数（FST）为0.104。但二者在所检测的8个位点上共享绝大多数等位基因，且检测到了显著的遗传混合现象。群体遗传混合分析（admixture analysis）结果显示，赤皮青冈与栎叶青冈中分别有11%和24%的个体，其被正确归类到对应物种的概率低于0.9。基于模型的检验表明，这种遗传混合不仅源于共享的祖先多态性，还由种间杂交所驱动。本研究采用溯祖（coalescent）方法估算了有效种群大小与基因流迁移率。估算结果显示，每世代向赤皮青冈和栎叶青冈迁移的有效个体数分别为8.843和71.98。理论上，每世代仅需1~10个迁移个体，即可阻止种群间出现完全的遗传分化。综合本研究结果来看，赤皮青冈与栎叶青冈间大概率普遍存在共享绝大多数等位基因的遗传混合现象，且该现象通过种间渐渗杂交得以维持。