Tunicates and not cephalochordates are the closest living relatives of vertebrates
Tunicates and not cephalochordates are the closest living relatives of vertebrates
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DOI：
10.1038/nature04336
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发表时间：
2006-02-23
期刊：
影响因子：
64.8
通讯作者：
Philippe, H
中科院分区：
文献类型：
--
作者：
Delsuc, F;Brinkmann, H;Philippe, H
被囊动物或尾脊索动物（尾尾动物、海鞘动物和海鞘动物）、头脊索动物（梭鱼）和脊椎动物（包括七鳃鳗和盲鳗）构成了现存的三个脊索动物类群。传统上，头脊索动物被认为是脊椎动物的近亲，而被囊动物代表了最早的脊索动物谱系（1,2）。这一观点主要是由头脊索动物和脊椎动物相对于被囊动物的整体形态相似性和明显增加的复杂性来证明的(2)。尽管它们对理解脊椎动物的起源至关重要(3)，脊索动物关系的系统发育研究提供了模棱两可的结果（4-7）。利用尾尾动物Oikopleura dioica的基因组测序，我们收集了来自14个后口动物和24个其他缓慢进化的外群物种的146个核基因（33,800个明确排列的氨基酸）的系统基因组数据集。在这里，我们展示了对这些数据集的系统发育分析提供了令人信服的证据，证明被囊动物而不是头脊索动物是脊椎动物的近亲。脊索动物的单一性仍然不确定，因为尽管没有显著的统计支持，头脊索动物却令人惊讶地与棘皮动物归为一类，这一假设需要用额外的数据来验证。这一新的系统发育方案促使形态学和古生物学数据的重新评估，并对以被囊动物和头脊索动物为模式动物的发育和基因组研究的解释具有重要意义。
Tunicates or urochordates (appendicularians, salps and sea squirts), cephalochordates (lancelets) and vertebrates (including lamprey and hagfish) constitute the three extant groups of chordate animals. Traditionally, cephalochordates are considered as the closest living relatives of vertebrates, with tunicates representing the earliest chordate lineage(1,2). This view is mainly justified by overall morphological similarities and an apparently increased complexity in cephalochordates and vertebrates relative to tunicates(2). Despite their critical importance for understanding the origins of vertebrates(3), phylogenetic studies of chordate relationships have provided equivocal results(4-7). Taking advantage of the genome sequencing of the appendicularian Oikopleura dioica, we assembled a phylogenomic data set of 146 nuclear genes (33,800 unambiguously aligned amino acids) from 14 deuterostomes and 24 other slowly evolving species as an outgroup. Here we show that phylogenetic analyses of this data set provide compelling evidence that tunicates, and not cephalochordates, represent the closest living relatives of vertebrates. Chordate monophyly remains uncertain because cephalochordates, albeit with a non-significant statistical support, surprisingly grouped with echinoderms, a hypothesis that needs to be tested with additional data. This new phylogenetic scheme prompts a reappraisal of both morphological and palaeontological data and has important implications for the interpretation of developmental and genomic studies in which tunicates and cephalochordates are used as model animals.