A New Spiralian Phylogeny Places the Enigmatic Arrow Worms among Gnathiferans
A New Spiralian Phylogeny Places the Enigmatic Arrow Worms among Gnathiferans
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DOI：
10.1016/j.cub.2018.11.042
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发表时间：
2019-01-21
期刊：
影响因子：
9.2
通讯作者：
Rokhsar, Daniel S.
中科院分区：
文献类型：
--
作者：
Marletaz, Ferdinand;Peijnenburg, Katja T. C. A.;Rokhsar, Daniel S.
Chaetognaths（箭蠕虫）是一个神秘的海洋动物群体，其系统发育位置仍然难以捉摸，部分原因是它们显示出与其他群体相关的发育和形态特征的混合[1，2]。特别是，目前还不清楚它们是否是原口动物的姐妹群[1，2]，主要的动物超分支之一，或者它们是否与一些螺旋门有更密切的关系[3，4]。解决毛颚类的系统发育位置和完善我们的理解之间的关系spiralians是必不可少的，以充分理解双边进化过程中的性格变化[5]。为了解决这些问题，我们为10种毛颚类动物生成了新的转录组，编制了一个广泛的基因组数据集，最大限度地提高了数据占用率和分类表示。我们采用了考虑分类群之间的速率和组成异质性的推断方法，以避免早期分析的局限性[6]。通过这种方式，我们大大提高了原口类生命树的分辨率。我们发现毛颚类与轮虫、颚口类和小颚类聚在一起，形成一个扩展的颚类分支，这个分支是其他螺旋虫的姐妹群[7，8]。我们的分析表明，以前提出的几个分组可能是由于系统性错误，我们提出了一个修订的组织Lophotrochozoa与三个主要分支：Tetraneuralia（软体动物和内肛），Lophophorata（腕足动物，phoronids，和外肛），和第三个未命名的分支收集环节动物，纽形动物，和扁形动物。考虑到经典的形态，发育和基因组特征，在这种拓扑结构表明二次损失的螺旋进化的一个基本趋势。
Chaetognaths (arrow worms) are an enigmatic group of marine animals whose phylogenetic position remains elusive, in part because they display a mix of developmental and morphological characters associated with other groups [1, 2]. In particular, it remains unclear whether they are a sister group to protostomes [1, 2], one of the principal animal superclades, or whether they bear a closer relationship with some spiralian phyla [3, 4]. Addressing the phylogenetic position of chaetognaths and refining our understanding of relationships among spiralians are essential to fully comprehend character changes during bilaterian evolution [5]. To tackle these questions, we generated new transcriptomes for ten chaetognath species, compiling an extensive phylogenomic data-set that maximizes data occupancy and taxonomic representation. We employed inference methods that consider rate and compositional heterogeneity across taxa to avoid limitations of earlier analyses [6]. In this way, we greatly improved the resolution of the protostome tree of life. We find that chaetognaths cluster together with rotifers, gnathostomulids, and micrognathozoans within an expanded Gnathifera clade and that this clade is the sister group to other spiralians [7, 8]. Our analysis shows that several previously proposed groupings are likely due to systematic error, and we propose a revised organization of Lophotrochozoa with three main clades: Tetraneuralia (mollusks and entoprocts), Lophophorata (brachiopods, phoronids, and ectoprocts), and a third unnamed clade gathering annelids, nemerteans, and platyhelminthes. Consideration of classical morphological, developmental, and genomic characters in light of this topology indicates secondary loss as a fundamental trend in spiralian evolution.