Are the Platyhelminthes a monophyletic primitive group? An assessment using 18S rDNA sequences
Are the Platyhelminthes a monophyletic primitive group? An assessment using 18S rDNA sequences
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DOI：
10.1093/oxfordjournals.molbev.a025785
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发表时间：
1997-05-01
影响因子：
10.7
通讯作者：
Riutort, M
中科院分区：
文献类型：
--
作者：
Carranza, S;Baguna, J;Riutort, M
在大多数动物学教科书中，扁形动物被描述为一个早期出现的分支，形成了所有其他双体动物的姐妹群。其他系统发育的建议，看到他们要么作为姐妹组的大部分原口动物或作为组来自原口动物的体腔祖先通过progenesis。在它们的正确的系统发育位置的主要困难是缺乏令人信服的synapomorphies为所有的扁形动物，这可能表明他们是多系的。此外，它们的内部系统发育关系仍然不确定。为了验证这些假设，新的完整的18 S rDNA序列从13种的“Turbellaria”已获得和比较发表的序列的其他2个“Turbellaria”，3种寄生的扁形动物，和几个双胚层和后口和原口三倍体。最大简约，最大似然，和邻居加入的方法被用来推断他们的同源性。结果表明，为了Catenulida形成一个独立的早期分支，并出现作为一个潜在的姐妹集团的其余的Bilateria，而其余的扁形动物（杆形目），其中包括寄生虫，形成一个明确的单系群密切相关的原口动物。Acoela目，形态上被认为是祖先的候选者，被证明是18 S rDNA基因的快时钟生物。因此，长分支的acoils和catenulids和acoils的采样不足，离开他们的位置仍然没有解决，并呼吁进一步的研究。在杆形动物门中，我们的分析表明：（1）巨口目和多枝目之间的关系密切，与其余的目形成了一个明确的姐妹群;（2）寄生的扁形动物在该类群的进化早期就出现了，与一个尚未确定的分支Nemertodermatida、Lecithoepitheliata、Prolecithophora、Proseriata、Tricladida和Rhabdocoela形成了一个姐妹群;（3）Seriata是并系群。
In most zoological textbooks, Platyhelminthes are depicted as an early-emerging clade forming the likely sister group of all the other Bilateria. Other phylogenetic proposals see them either as the sister group of most of the Protostomia or as group derived from protostome coelomate ancestors by progenesis. The main difficulty in their correct phylogenetic placing is the lack of convincing synapomorphies for all Platyhelminthes, which may indicate that they are polyphyletic. Moreover, their internal phylogenetic relationships are still uncertain. To test these hypotheses, new complete 18S rDNA sequences from 13 species of ''Turbellaria'' have been obtained and compared to published sequences of 2 other ''Turbellaria,'' 3 species of parasitic Platyhelminthes, and several diploblastic and deuterostome and protostome triploblastics. Maximum-parsimony, maximum-likelihood, and neighbour-joining methods were used to infer their phylogeny. The results show the order Catenulida to form an independent early-branching clade and emerge as a potential sister group of the rest of the Bilateria, while the rest of Platyhelminthes (Rhabditophora), which includes the parasites, form a clear monophyletic group closely related to the protostomes. The order Acoela, morphologically considered as candidates to be ancestral, are shown to be fast-clock organisms for the 18S rDNA gene. Hence, long-branching of acoels and insufficient sampling of catenulids and acoels leave their position still unresolved and call for further studies. Within the Rhabditophora, our analyses suggest (1) a close relationship between orders Macrostomida and Polycladida, forming a clear sister group to the rest of orders; (2) that parasitic platyhelminthes appeared early in the evolution of the group and form a sister group to a still-unresolved clade made by Nemertodermatida, Lecithoepitheliata, Prolecithophora, Proseriata, Tricladida, and Rhabdocoela; and (3) that Seriata is paraphyletic.