A recent reclassification of diatoms based on phylogenies recovered using the nuclear-encoded small subunit ribosomal RNA (SSU rRNA) gene contains three major classes, Coscinodiscophyceae, Mediophyceae and the Bacillariophyceae (the CMB hypothesis). We evaluated this with a sequence alignment of 1336 protist and heterokont algae SSU rRNAs, which includes 673 diatoms. Sequences were aligned to maintain structural elements conserved within this dataset. Parsimony analysis rejected the CMB hypothesis, albeit weakly. Morphological data are also incongruent with this recent CMB hypothesis of three diatom clades. We also re-analysed a recently published dataset that purports to support the CMB hypothesis. Our re-analysis found that the original analysis had not converged on the true bipartition posterior probability distribution, and rejected the CMB hypothesis. Thus we conclude that a reclassification of the evolutionary relationships of the diatoms according to the CMB hypothesis is premature.

中文翻译：

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核编码的 SSU rDNA 在解决硅藻系统发育方面的局限性


最近，基于使用核编码小亚基核糖体 RNA (SSU rRNA) 基因恢复的系统发育对硅藻进行了重新分类，其中包含三个主要类别：圆盘藻纲、中间藻纲和硅藻纲（CMB 假说）。我们通过 1336 个原生生物和异质藻 SSU rRNA（其中包括 673 个硅藻）的序列比对对此进行了评估。序列被对齐以保持该数据集中保守的结构元素。简约分析否定了 CMB 假说，尽管效果很弱。形态学数据也与最近的三个硅藻分支的 CMB 假设不一致。我们还重新分析了最近发布的数据集，该数据集旨在支持 CMB 假设。我们的重新分析发现，原来的分析没有收敛于真实的二分后验概率分布，并拒绝了CMB假设。因此，我们得出结论，根据 CMB 假说对硅藻的进化关系进行重新分类还为时过早。