Division of Environmental and Evolutionary Biology, Sir Harold Mitchell Building, University of St. Andrews, St. Andrews KY16 9TH, UK.
Am J Bot. 2003 Jun;90(6):931-6. doi: 10.3732/ajb.90.6.931.
Saxifraga oppositifolia (Saxifragaceae) is an important model system for the evolution of Arctic-Alpine plant species. Sequences of the psbA-trnH intergenic spacer of chloroplast DNA and of the internal transcribed spacer region, ITS1-5.8S-ITS2, of the nuclear ribosomal DNA were used to investigate the intraspecific evolution and phylogeography of this species. Samples from nearly the species' entire circumpolar distribution were included in the analysis as well as samples from the closely related taxa S. smalliana from Alaska and S. blepharophylla and S. biflora from the Alps (S. aizoides served as outgroup). These latter taxa showed a low number of parsimony informative characters, in both cpDNA and ITS sequences, which separated them from S. oppositifolia. Two main cpDNA haplotypes were detected within S. oppositifolia, one with a Eurasian distribution and one with an East Asian-North American distribution. This confirmed the existence of two cpDNA lineages with different geographical distributions in this species, which had previously been reported based on a RFLP analysis. The ITS phylogeny was not useful with respect to the intraspecific evolution and phylogeography of S. oppositifolia, because it showed a largely unresolved topology with low statistical support. The cpDNA sequence analysis, however, also suggested a putative long-distance dispersal event. All investigated taxa had cpDNA haplotypes that were congruent with their geographical origin rather than their phylogeny. This could point to putative lineage sorting in S. oppositifolia and related taxa.
珠芽景天（虎耳草科）是研究北极高山植物物种进化的重要模式系统。本研究利用叶绿体基因组 psbA-trnH 基因间隔区和核核糖体 DNA 内转录间隔区（ITS1-5.8S-ITS2）序列，对该物种的种内进化和系统地理学进行了分析。本研究分析了近种的全环极分布的样本，以及来自阿拉斯加的近缘种珠芽景天 smalliana、来自阿尔卑斯山的珠芽景天 blepharophylla 和 biflora（Aizoides 作为外类群）。这些后分类群在 cpDNA 和 ITS 序列中都显示出数量较少的简约信息特征，将它们与珠芽景天分开。在珠芽景天内检测到两种主要的 cpDNA 单倍型，一种具有欧亚分布，另一种具有东亚-北美分布。这证实了该物种存在两种 cpDNA 谱系，具有不同的地理分布，这在之前基于 RFLP 分析的研究中已经报道过。ITS 系统发育树对于珠芽景天的种内进化和系统地理学没有用处，因为它显示出拓扑结构很大程度上未解决，统计支持度低。然而，cpDNA 序列分析也表明了一个可能的长距离扩散事件。所有被调查的分类群都有与它们的地理起源而不是它们的系统发育相一致的 cpDNA 单倍型。这可能表明珠芽景天和相关分类群中存在潜在的谱系分选。
