nrDNA internal and external transcribed spacer sequences for investigating the systematics of Dieteria

The objectives of this research were to assess variation in nrDNA internal
and external transcribed spacer (ITS and ETS) sequences of the
morphologically diverse genus Dieteria and to determine how well the
results of phylogenetic analysis corresponded with morphological
variation, taxonomy, and geographic distribution. The first of two
analyses included 39 samples from throughout the range of the genus
representing 13 of the 16 currently accepted varieties, with ITS and ETS
sequences combined to obtain the greatest resolution possible. This
analysis produced phylogenies containing three major clades. One of the
three consisted of samples from Washington, Oregon, and northern
California. The second one included samples from southern California and
western Arizona, plus additional ones from northern California, northern
Nevada, and southeastern Idaho. The third clade was the largest and
consisted of samples from the remaining part of the distribution of
Dieteria. Comparison of the results with current taxonomy and
morphological characteristics showed little correspondence between the
molecular phylogeny and either taxonomy or morphology, suggesting multiple
occurrences of convergent evolution. There were some correlations with
geographic distributions. Except for the second and third clades’
distributions overlapping in some areas, the distributions of the three
were mostly distinct from one another; smaller clades within them were
also correlated with distributions. The second analysis included cloned
sequences of five additional samples that were shown by initial sequencing
efforts to contain many polymorphic nucleotide positions. In the results,
the ITS and/or ETS for all five samples were placed in multiple positions
some distance apart, indicating that these samples obtained their ITS
and/or ETS sequences from distantly related ancestors through
hybridization between members of two of the three major clades.

本研究旨在评估形态多样性丰富的Dieteria属中核糖体DNA（nrDNA）内部转录间隔区（ITS）与外部转录间隔区（ETS）序列的变异情况，并探究系统发育分析结果与形态变异、分类学及地理分布之间的契合度。两项分析中的第一项涵盖了该属全分布区的39份样本，代表了当前公认的16个变种中的13个；研究将ITS与ETS序列合并，以获得尽可能高的解析度。该分析构建的系统发育树包含三个主要分支。其中一个分支由来自华盛顿州、俄勒冈州及加利福尼亚州北部的样本组成；第二个分支包含加利福尼亚州南部和亚利桑那州西部的样本，以及来自加利福尼亚州北部、内华达州北部和爱达荷州东南部的额外样本；第三个分支规模最大，涵盖了Dieteria属其余分布区域的样本。将结果与当前分类学及形态特征对比后发现，分子系统发育与分类学或形态学之间的契合度较低，这表明趋同进化（convergent evolution）可能多次发生。研究结果与地理分布存在一定关联：除第二和第三分支的分布区域在部分地区重叠外，三个分支的分布总体上彼此独立；分支内部的次级小分支也与分布区域相关。第二项分析纳入了5份额外样本的克隆序列，初步测序显示这些样本存在大量多态性核苷酸位点。结果表明，所有5份样本的ITS和/或ETS序列分布在多个相距较远的位置，这意味着这些样本通过三个主要分支中两个分支成员间的杂交，从亲缘关系较远的祖先处获得了其ITS和/或ETS序列。