Center for Biosystems Research, University of Maryland Biotechnology Institute, College Park, Maryland 20742, USA.
Nature. 2010 Feb 25;463(7284):1079-83. doi: 10.1038/nature08742. Epub 2010 Feb 10.
The remarkable antiquity, diversity and ecological significance of arthropods have inspired numerous attempts to resolve their deep phylogenetic history, but the results of two decades of intensive molecular phylogenetics have been mixed. The discovery that terrestrial insects (Hexapoda) are more closely related to aquatic Crustacea than to the terrestrial centipedes and millipedes (Myriapoda) was an early, if exceptional, success. More typically, analyses based on limited samples of taxa and genes have generated results that are inconsistent, weakly supported and highly sensitive to analytical conditions. Here we present strongly supported results from likelihood, Bayesian and parsimony analyses of over 41 kilobases of aligned DNA sequence from 62 single-copy nuclear protein-coding genes from 75 arthropod species. These species represent every major arthropod lineage, plus five species of tardigrades and onychophorans as outgroups. Our results strongly support Pancrustacea (Hexapoda plus Crustacea) but also strongly favour the traditional morphology-based Mandibulata (Myriapoda plus Pancrustacea) over the molecule-based Paradoxopoda (Myriapoda plus Chelicerata). In addition to Hexapoda, Pancrustacea includes three major extant lineages of 'crustaceans', each spanning a significant range of morphological disparity. These are Oligostraca (ostracods, mystacocarids, branchiurans and pentastomids), Vericrustacea (malacostracans, thecostracans, copepods and branchiopods) and Xenocarida (cephalocarids and remipedes). Finally, within Pancrustacea we identify Xenocarida as the long-sought sister group to the Hexapoda, a result confirming that 'crustaceans' are not monophyletic. These results provide a statistically well-supported phylogenetic framework for the largest animal phylum and represent a step towards ending the often-heated, century-long debate on arthropod relationships.
节肢动物具有显著的古老性、多样性和生态意义，这激发了人们无数次尝试来解决它们的深层系统发育历史，但 20 年来密集的分子系统发育学研究的结果喜忧参半。陆生昆虫（六足动物）与水生甲壳动物的亲缘关系比与陆生的蜈蚣和倍足纲动物（多足动物）更为密切，这一发现是早期的，尽管是例外的成功。更常见的是，基于有限的分类单元和基因样本的分析产生了不一致的、支持较弱且对分析条件高度敏感的结果。在这里，我们展示了来自超过 75 种节肢动物的 62 个单拷贝核蛋白编码基因的 41 千碱基以上的对齐 DNA 序列的似然、贝叶斯和简约分析的有力支持结果。这些物种代表了每个主要的节肢动物谱系，外加 5 种缓步动物和有爪动物作为外群。我们的结果强烈支持泛甲壳类动物（六足动物加甲壳动物），但也强烈支持基于传统形态的有颚类（多足动物加泛甲壳动物），而不是基于分子的螯肢类（多足动物加螯肢动物）。除了六足动物，泛甲壳类动物还包括三种主要的现存“甲壳类”谱系，每一种都跨越了显著的形态差异范围。这些是寡甲类（介形类、迷齿甲目、鳃足类和六足类）、真甲壳类（软甲纲、端足目、桡足类和鳃足类）和外甲类（头虾目和栉虾目）。最后，在泛甲壳动物中，我们确定外甲类是六足动物长期以来寻求的姐妹群，这一结果证实了“甲壳类”不是单系的。这些结果为最大的动物门提供了一个统计上支持良好的系统发育框架，并代表着朝着结束节肢动物关系这一长达一个世纪的激烈争论迈出了一步。
