Giribet G, Carranza S, Baguñà J, Riutort M, Ribera C
Department de Biologia Animal, Facultat de Biologia, Universitat de Barcelona, Spain.
Mol Biol Evol. 1996 Jan;13(1):76-84. doi: 10.1093/oxfordjournals.molbev.a025573.
The complete 18S rDNA gene sequence of Macrobiotus group hufelandi (Tardigrada) was obtained and aligned with 18S rDNA and rRNA gene sequences of 24 metazoans (mainly protostomes). Discrete character (maximum-parsimony) and distance (neighbor-joining) methods were used to infer their phylogeny. The evolution of bootstrap proportions with sequence length (pattern of resolved nodes, PRN) was studied to test the resolution of the nodes in neighbor-joining trees. The results show that arthropods are monophyletic. Tardigrades represent the sister group of arthropods (in parsimony analyses) or they are related with crustaceans (distance analysis and PRN). Arthropoda are divided into two main evolutionary lines, the Hexapoda + Crustacea line (weakly supported), and the Myriapoda + Chelicerata line. The Hexapoda + Crustacea line includes Pentastomida, but the internal resolution is far from clear. The Insecta (Ectognatha) are monophyletic, but no evidence for the monophyly of Hexapoda is found. The Chelicerata are a monophyletic group and the Myriapoda cluster close to Arachnida. Overall, the results obtained represent the first molecular evidence for a Tardigrada + Arthropoda clade. In addition, the congruence between molecular phylogenies of the Arthropoda from other authors and this obtained here indicates the need to review those obtained solely on morphological characters.
获得了胡氏大生熊虫（缓步动物门）完整的18S核糖体DNA基因序列，并将其与24种后生动物（主要是原口动物）的18S核糖体DNA和核糖体RNA基因序列进行比对。采用离散性状（最大简约法）和距离（邻接法）方法推断它们的系统发育。研究了自展比例随序列长度的演化（解析节点模式，PRN）以检验邻接树中节点的解析度。结果表明，节肢动物是单系的。缓步动物代表节肢动物的姐妹类群（在简约分析中），或者它们与甲壳类动物相关（距离分析和PRN）。节肢动物门分为两个主要进化谱系，即六足动物 + 甲壳动物谱系（支持力度较弱）和多足动物 + 螯肢动物谱系。六足动物 + 甲壳动物谱系包括舌形动物门，但内部解析度远不清楚。昆虫纲（外颚类）是单系的，但未发现六足动物单系性的证据。螯肢动物是一个单系类群，多足动物聚集在蛛形纲附近。总体而言，所获得的结果代表了缓步动物门 + 节肢动物门分支的首个分子证据。此外，其他作者对节肢动物的分子系统发育与本文所获结果之间的一致性表明，有必要重新审视仅基于形态特征所获得的结果。
