Negrisolo Enrico, Maistro Silvia, Incarbone Matteo, Moro Isabella, Dalla Valle Luisa, Broady Paul A, Andreoli Carlo
Department of Biology and Centro Ricerche Interdipartimentale Biotecnologie Innovative (CRIBI), University of Padova, Via U. Bassi 58/B, 35131 Padova, Italy.
Mol Phylogenet Evol. 2004 Oct;33(1):156-70. doi: 10.1016/j.ympev.2004.04.016.
Xanthophyceae are a group of heterokontophyte algae. Few molecular studies have investigated the evolutionary history and phylogenetic relationships of this class. We sequenced the nuclear-encoded SSU rDNA and chloroplast-encoded rbcL genes of several xanthophycean species from different orders, families, and genera. Neither SSU rDNA nor rbcL genes show intraspecific sequence variation and are good diagnostic markers for characterization of problematic species. New sequences, combined with those previously available, were used to create different multiple alignments. Analyses included sequences from 26 species of Xanthophyceae plus three Phaeothamniophyceae and two Phaeophyceae taxa used as outgroups. Phylogenetic analyses were performed according to Bayesian inference, maximum likelihood, and maximum parsimony methods. We explored effects produced on the phylogenetic outcomes by both taxon sampling as well as selected genes. Congruent results were obtained from analyses performed on single gene multiple alignments as well as on a data set including both SSU rDNA and rbcL sequences. Trees obtained in this study show that several currently recognized xanthophycean taxa do not form monophyletic groups. The order Mischococcales is paraphyletic, while Tribonematales and Botrydiales are polyphyletic even if evidence for the second order is not conclusive. Botrydiales and Vaucheriales, both including siphonous taxa, do not form a clade. The families Botrydiopsidaceae, Botryochloridaceae, and Pleurochloridaceae as well as the genera Botrydiopsis and Chlorellidium are polyphyletic. The Centritractaceae and the genus Bumilleriopsis also appear to be polyphyletic but their monophyly cannot be completely rejected with current evidence. Our results support morphological convergence at any taxonomic rank in the evolution of the Xanthophyceae. Finally, our phylogenetic analyses exclude an origin of the Xanthophyceae from a Vaucheria-like ancestor and favor a single early origin of the coccoid cell form.
黄藻纲是一群不等鞭毛类藻类。很少有分子研究调查过该纲的进化历史和系统发育关系。我们对来自不同目、科和属的几种黄藻纲物种的核编码小亚基核糖体DNA（SSU rDNA）和叶绿体编码的rbcL基因进行了测序。SSU rDNA和rbcL基因都未显示种内序列变异，是鉴定疑难物种的良好诊断标记。新序列与先前可得的序列相结合，用于创建不同的多序列比对。分析包括来自26种黄藻纲物种的序列，外加用作外类群的3种褐管藻纲和2种褐藻纲分类单元。根据贝叶斯推断、最大似然法和最大简约法进行系统发育分析。我们探究了分类群抽样以及所选基因对系统发育结果产生的影响。对单基因多序列比对以及包含SSU rDNA和rbcL序列的数据集进行的分析获得了一致的结果。本研究中得到的树状图表明，目前认可的几个黄藻纲分类单元并未形成单系类群。 Mischococcales目是并系的，而Tribonematales目和Botrydiales目是多系的，尽管关于第二个目的证据并不确凿。 Botrydiales目和Vaucheriales目都包含管状体分类群，但并未形成一个分支。 Botrydiopsidaceae科、Botryochloridaceae科和Pleurochloridaceae科以及Botrydiopsis属和Chlorellidium属都是多系的。 Centritractaceae科和Bumilleriopsis属似乎也是多系的，但根据目前的证据不能完全排除它们的单系性。我们的结果支持黄藻纲进化过程中任何分类等级上的形态趋同。最后，我们的系统发育分析排除了黄藻纲起源于类似Vaucheria属祖先的可能性，并支持球状体细胞形式有一个单一的早期起源。
