Molecular evidence for sectional classification of shrub willows (Salix L. subg. Chamaetia/Vetrix) based on RAD sequencing data

下一代测序工具的兴起极大地增加了研究人员分析非模式植物的机会。系统基因组学的发展使重建生物体的进化史和基于大量测序数据评估现有的分类概念成为可能。然而，大多数方法和工具都是用于二倍体属或在有限的地理区域内定义明确的种群。因此，处理分类上困难的植物，频繁杂交，表现出网状进化，多倍体和渐渗仍然是具有挑战性的。种类丰富的柳属，特别是灌木柳树（亚属）。Chamaetia/Vetrix)是这样一个分类上具有挑战性的树木和灌木群，发生在北半球。本种为雌雄异株，表型可塑性强，杂交频繁，倍性从二倍体到八倍体不等。现有的分类修订以形态学为基础，仅限于局部区域。据他们介绍，Chamaetia/Vetrix包括300多个物种，分为大约40个部分。然而，柳属植物的整体分类还远未解决。尽管对柳属植物进行了长期的研究，但传统的种、段分类尚未得到分子标记的检验。其主要原因是传统标记系统中信息特征的缺失。然而，新的测序技术，如RAD测序产生成千上万的可变字符。在拟建项目中，将利用高信息量的RAD测序数据对灌木柳树的剖面分类和复杂演化进行分析，进行全面采样，包括所有描述的剖面。一个很好的解决系统发育，包括几个物种的每段覆盖分布范围，将产生一个遗传框架，结合形态学特征编码将有助于解开在柳树的分类挑战。在分子数据的基础上，对多倍体进行具体分析。最后，应建立hyRAD，这是一种允许将降解DNA（例如来自植物标本馆材料）纳入RAD测序方法的方法。灌木柳树的时空演变将通过对一个年代系统发育的生物地理分析来重建。

The rise of next generation sequencing tools massively increases the opportunities of researchers to analyze non-model plants. The developments in phylogenomics make it possible to reconstruct the evolutionary history of organisms and to assess existing taxonomic concepts based on impressive amounts of sequenced data. However, most methods and tools are used for diploid genera or well-defined species groups in a restricted geographical region. Thus, dealing with taxonomically difficult plants that are frequently hybridizing, show reticulate evolution, polyploidy, and introgression is still challenging. The species-rich genus Salix L. and especially shrub willows (subg. Chamaetia/Vetrix) are such a taxonomically challenging group of trees and shrubs occurring in the Northern Hemisphere. The species are dioecious, show phenotypic plasticity, hybridize frequently and their ploidy level range from diploid to octoploid. Existing taxonomic revisions were based on morphology and restricted to local regions. According them, Chamaetia/Vetrix includes more than 300 species classified in about 40 sections. However, the overall taxonomy in Salix is far from resolved. Despite the long research in Salix, the traditional classification of species and sections has never been tested with molecular markers. The main reason was the lack of informative characters in traditional marker systems. However, new sequencing techniques as RAD sequencing produce ten thousands of variable characters. In the proposed project, the sectional classification and complex evolution of shrub willows shall be analyzed with the highly informative RAD sequencing data for a comprehensive sampling including all described sections. A well-resolved phylogeny including several species per section covering the distributional range will result in a genetic framework that combined with morphological character coding will help to disentangle the taxonomic challenges in Salix. Based on the molecular data, specific analyses on polyploidy shall be performed. Finally, hyRAD shall be established, a method that allows the inclusion of degraded DNA (e.g. from herbarium material) into a RAD sequencing approach. The spatio-temporal evolution of shrub willows will be reconstructed by biogeographical analyses of a dated phylogeny.