PDF(Pubmed)
Abstract：
Almost all species in the genus Salix (willow) are dioecious and willows have variable sex-determining systems, the role of this variation in maintaining species barriers is relatively untested. We first analyzed the sex determination systems (SDS) of two species, Salix cardiophylla and Salix interior, whose positions in the Salix phylogeny make them important for understanding a sex chromosome turnover that has been detected in their relatives, and that changed the system from male (XX/XY) to female (ZW/ZZ) heterogamety. We show that both species have male heterogamety, with sex-linked regions (SLRs) on chromosome 15 (termed a 15XY system). The SLRs occupy 21.3% and 22.8% of the entire reference chromosome, respectively. By constructing phylogenetic trees, we determined the phylogenetic positions of all the species with known SDSs. Reconstruction of ancestral SDS character states revealed that the 15XY system is likely the ancestral state in willows. Turnovers of 15XY to 15ZW and 15XY to 7XY likely contributed to early speciation in Salix and gave rise to major groups of the Vetrix and Salix clades. Finally, we tested introgression among species in the phylogenetic trees based on both autosomes and SLRs separately. Frequent introgression was observed among species with 15XY, 15ZW, and 7XY on autosomes, in contrast to the SLR datasets, which showed less introgression, and in particular no gene flow between 15ZW and 7XY species. We argue that, although SDS turnovers in willow speciation may not create complete reproductive barriers, the evolution of SLRs plays important roles in preventing introgression and maintaining species boundaries.
摘要：
柳属（柳属）几乎所有物种都是雌雄异株，柳属具有可变的性别决定系统，这种变化在维持物种屏障中的作用是相对未经测试的。我们首先分析了两个物种的性别决定系统（SDS），沙柳和沙柳内部，他们在柳树系统发育中的位置使他们对于理解在他们的亲属中检测到的性染色体周转很重要，这将系统从男性（XX/XY）改变为女性（ZW/ZZ）的异性恋。我们表明这两个物种都有雄性异性恋，在15号染色体上具有性别连锁区域（SLR）（称为15XY系统）。SLR占整个参考染色体的21.3％和22.8％，分别。通过构建系统发育树，我们确定了所有具有已知SDS的物种的系统发育位置。祖先SDS字符状态的重建表明，15XY系统可能是柳树的祖先状态。15XY至15ZW和15XY至7XY的失误可能导致了柳柳的早期物种形成，并导致了Vetrix和柳柳进化枝的主要群体。最后,我们分别基于常染色体和SLR测试了系统发育树中物种之间的渗入。在15XY的物种中观察到频繁的渗入，15ZW,和7XY在常染色体上，与SLR数据集相比，表现出较少的渗入，特别是15ZW和7XY物种之间没有基因流动。我们认为，虽然柳树物种形成的SDS失误可能不会造成完全的繁殖障碍，SLR的进化在防止渗入和维持物种边界方面发挥着重要作用。
