Deep sequencing of amplicons reveals widespread intraspecific hybridization and multiple origins of polyploidy in big sagebrush (Artemisia tridentata)

PREMISE OF THE STUDY: Hybridization has played an important role in the evolution and ecological adaptation in diploid and polyploid plants. Artemisia tridentata (Asteraceae) tetraploids are extremely widespread and of great ecological importance. These tetraploids are often taxonomically identified as A. tridentata ssp. wyomingensis, or as autotetraploids of diploid subspecies tridentata and vaseyana. Few details are available as to how these tetraploids are formed or how they are related to diploid subspecies. METHODS: We used amplicon sequencing to assess phylogenetic relationships among three recognized subspecies: tridentata, vaseyana and wyomingensis. DNA sequence data from putative genes were pyrosequenced and assembled from 329 samples. Nucleotide diversity and putative haplotypes were estimated from the high-read coverage. Phylogenies were constructed from Bayesian coalescence and neighbor-net network analyses. KEY RESULTS: Analyses support distinct diploid subspecies of triden...

研究背景：杂交（Hybridization）在二倍体与多倍体植物的演化及生态适应过程中发挥了重要作用。三齿蒿（Artemisia tridentata，菊科Asteraceae）的四倍体类群分布极广，且具有极高的生态价值。这类四倍体通常在分类学上被鉴定为三齿蒿怀俄明亚种（A. tridentata ssp. wyomingensis），或是二倍体亚种tridentata与vaseyana的同源四倍体。目前针对这类四倍体的起源路径，以及其与二倍体亚种间的亲缘关联，已知细节仍较为匮乏。
研究方法：本研究采用扩增子测序（amplicon sequencing）技术，解析三齿蒿三个已确认亚种（tridentata、vaseyana与wyomingensis）的系统发育关系。研究人员从329份样本中获取候选基因的DNA序列数据，经焦磷酸测序（pyrosequencing）完成组装；基于高测序覆盖度数据估算核苷酸多样性（nucleotide diversity）与候选单倍型；通过贝叶斯溯祖分析与邻分网络（neighbor-net network）分析构建系统发育树。
主要结果：分析结果支持triden...的二倍体亚种为独立类群。