Dunn Casey W, Pugh Philip R, Haddock Steven H D
Department of Ecology and Evolutionary Biology, Yale University, New Haven, Connecticut, USA.
Syst Biol. 2005 Dec;54(6):916-35. doi: 10.1080/10635150500354837.
Siphonophores are a group of pelagic colonial hydrozoans (Cnidaria) that have long been of general interest because of the division of labor between the polyps and medusae that make up these "superorganisms." These polyps and medusae are each homologous to free living animals but are generated by an incomplete asexual budding process that leaves them physiologically integrated. They are functionally specialized for different tasks and are precisely organized within each colony. The number of functional types of polyps and medusae varies across taxa, and different authors have used this character to construct phylogenies polarized in opposite directions, depending on whether they thought siphonophore evolution proceeded by a reduction or an increase in functional specialization. We have collected taxa across all major groups of siphonophores, many of which are found exclusively in the deep sea, using remotely operated underwater vehicles (ROVs) and by SCUBA diving from ships in the open ocean. We have used 52 siphonophores and four outgroup taxa to estimate the siphonophore phylogeny with molecular data from the nuclear small subunit ribosomal RNA gene (18S) and the mitochondrial large subunit ribosomal RNA gene (16S). Parsimony reconstructions indicate that functionally specialized polyps and medusae have been gained and lost across the phylogeny. Maximum likelihood and Bayesian analyses of morphological data suggest that the transition rate for decreased functional specialization is greater than the transition rate for increased functional specialization for three out of the four investigated categories of polyps and medusae. The present analysis also bears on several long-standing questions about siphonophore systematics. It indicates that the cystonects are sister to all other siphonophores, a group that we call the Codonophora. We also find that the Calycophorae are nested within the Physonectae, and that the Brachystelia, a historically recognized grouping of short-stemmed taxa, are polyphyletic. [Cnidaria; colonial animals; deep sea; division of labor; functional specialization; Hydrozoa; phylogenetics; Siphonophores.].
管水母目动物是一类海洋群体水螅虫（刺胞动物门），长期以来一直备受关注，因为构成这些“超级生物体”的水螅体和水母体之间存在分工。这些水螅体和水母体各自与自由生活的动物同源，但通过不完全的无性出芽过程产生，这使得它们在生理上相互整合。它们在功能上专门从事不同的任务，并在每个群体中精确组织。水螅体和水母体的功能类型数量因分类群而异，不同的作者根据他们认为管水母目的进化是通过功能特化的减少还是增加，利用这一特征构建了方向相反的系统发育树。我们使用遥控水下航行器（ROV）并通过在公海中从船上进行水肺潜水，收集了管水母目所有主要类群的分类群，其中许多仅在深海中发现。我们使用了52种管水母目动物和4个外类群分类群，利用来自核小亚基核糖体RNA基因（18S）和线粒体大亚基核糖体RNA基因（16S）的分子数据来估计管水母目的系统发育。简约重建表明，功能特化的水螅体和水母体在整个系统发育过程中有所增减。对形态学数据的最大似然法和贝叶斯分析表明，在所研究的四类水螅体和水母体中，有三类功能特化减少的转变率大于功能特化增加的转变率。目前的分析也涉及到几个关于管水母目系统分类学的长期问题。它表明囊泳亚目是所有其他管水母目的姐妹群，我们将这一组称为钟泳亚目。我们还发现，胞泳亚目嵌套在管水母亚目中，并且短柄类群这一历史上公认的分类群是多系的。[刺胞动物门；群体动物；深海；分工；功能特化；水螅虫纲；系统发育学；管水母目动物。]
