Vergleichende Zoologie, Institut für Biologie, Humboldt-Universität zu Berlin, Philippstrasse 13, Haus 2, 10115, Berlin, Germany.
Animal Evolution and Biodiversity, J-F-Blumenbach Institute for Zoology & Anthropology, Georg-August-University Göttingen, Untere Karspüle 2, 37073, Göttingen, Germany.
Cladistics. 2020 Jun;36(3):259-300. doi: 10.1111/cla.12405. Epub 2019 Nov 13.
With approximately 3000 marine species, Tunicata represents the most disparate subtaxon of Chordata. Molecular phylogenetic studies support Tunicata as sister taxon to Craniota, rendering it pivotal to understanding craniate evolution. Although successively more molecular data have become available to resolve internal tunicate phylogenetic relationships, phenotypic data have not been utilized consistently. Herein these shortcomings are addressed by cladistically analyzing 117 phenotypic characters for 49 tunicate species comprising all higher tunicate taxa, and five craniate and cephalochordate outgroup species. In addition, a combined analysis of the phenotypic characters with 18S rDNA-sequence data is performed in 32 OTUs. The analysis of the combined data is congruent with published molecular analyses. Successively up-weighting phenotypic characters indicates that phenotypic data contribute disproportionally more to the resulting phylogenetic hypothesis. The strict consensus tree from the analysis of the phenotypic characters as well as the single most parsimonious tree found in the analysis of the combined dataset recover monophyletic Appendicularia as sister taxon to the remaining tunicate taxa. Thus, both datasets support the hypothesis that the last common ancestor of Tunicata was free-living and that ascidian sessility is a derived trait within Tunicata. "Thaliacea" is found to be paraphyletic with Pyrosomatida as sister taxon to monophyletic Ascidiacea and the relationship between Doliolida and Salpida is unresolved in the analysis of morphological characters; however, the analysis of the combined data reconstructs Thaliacea as monophyletic nested within paraphyletic "Ascidiacea". Therefore, both datasets differ in the interpretation of the evolution of the complex holoplanktonic life history of thaliacean taxa. According to the phenotypic data, this evolution occurred in the plankton, whereas from the combined dataset a secondary transition into the plankton from a sessile ascidian is inferred. Besides these major differences, both analyses are in accord on many phylogenetic groupings, although both phylogenetic reconstructions invoke a high degree of homoplasy. In conclusion, this study represents the first serious attempt to utilize the potential phylogenetic information present in phenotypic characters to elucidate the inter-relationships of this diverse marine taxon in a consistent cladistic framework.
被囊动物门拥有大约 3000 种海洋物种，是脊索动物中差异最大的亚类群。分子系统发育研究支持把被囊动物门作为头索动物的姐妹群，这对头索动物的进化研究至关重要。尽管越来越多的分子数据可用于解决内部被囊动物的系统发育关系，但表型数据并未得到一致利用。本文通过对包含所有高等被囊动物类群以及 5 个头索动物和半索动物外群物种的 49 种被囊动物的 117 个表型特征进行分支分析，解决了这些缺点。此外，还对 32 个 OTU 的表型特征与 18S rDNA 序列数据进行了联合分析。联合数据分析的结果与已发表的分子分析结果一致。逐步增加表型特征的权重表明，表型数据对最终的系统发育假说有不成比例的贡献。基于表型特征分析的严格一致树以及在联合数据集分析中找到的单个最简约树都恢复了尾索动物作为有尾类动物的姐妹群。因此，两个数据集都支持这样的假说，即被囊动物的最后共同祖先为自由生活，尾索动物的固着是被囊动物中的衍生特征。“海鞘类”被发现为并系群，而火体虫目是有尾类动物的姐妹群，位于多毛类动物和柱头虫类的分支之外；然而，在形态特征分析中，多毛类动物和柱头虫类之间的关系未得到解决；然而，在联合数据集的分析中，海鞘类被重建为并系群，嵌套在多毛类动物的“被囊动物”中。因此，两个数据集在解释尾索动物类群复杂的浮游生物生活史的进化方面存在差异。根据表型数据，这种进化发生在浮游生物中，而从联合数据集推断，它是从固着的尾索动物向浮游生物的二次过渡。除了这些主要差异外，两个分析在许多系统发育分组上是一致的，尽管两个系统发育重建都涉及高度的趋同进化。总之，本研究代表了首次认真尝试利用表型特征中存在的潜在系统发育信息，在一致的分支框架内阐明这个多样化的海洋类群的相互关系。
