Department of Biological Sciences and Alabama Museum of Natural History, University of Alabama, Tuscaloosa, AL 35487, USA.
Department of Biological Sciences, Auburn University, Auburn, AL 36830, USA.
Mol Phylogenet Evol. 2018 Apr;121:166-173. doi: 10.1016/j.ympev.2018.01.005. Epub 2018 Jan 9.
Tunicata, a diverse clade of approximately 3000 described species of marine, filter-feeding chordates, is of great interest to researchers because tunicates are the closest living relatives of vertebrates and they facilitate comparative studies of our own biology. The group also includes numerous invasive species that cause considerable economic damage and some species of tunicates are edible. Despite their diversity and importance, relationships among major lineages of Tunicata are not completely resolved. Here, we supplemented public data with transcriptomes from seven species spanning the diversity of Tunicata and conducted phylogenomic analyses on data sets of up to 798 genes. Sensitivity analyses were employed to examine the influences of reducing compositional heterogeneity and branch-length heterogeneity. All analyses maximally supported a monophyletic Tunicata within Olfactores (Vertebrata + Tunicata). Within Tunicata, all analyses recovered Appendicularia sister to the rest of Tunicata and confirmed (with maximal support) that Thaliacea is nested within Ascidiacea. Stolidobranchia is the sister taxon to all other tunicates except Appendicularia. In most analyses, phlebobranch tunicates were recovered paraphyletic with respect to Aplousobranchia. Support for this topology varied but was strong in some cases. However, when only the 50 best genes based on compositional heterogeneity were analysed, we recovered Phlebobranchia and Aplousobranchia reciprocally monophyletic with strong support, consistent with most traditional morphology-based hypotheses. Examination of internode certainty also cast doubt on results of phlebobranch paraphyly, which may be due to limited taxon sampling. Taken together, these results provide a higher-level phylogenetic framework for our closest living invertebrate relatives.
被囊动物门，是约 3000 种已描述的海洋滤食性脊索动物的一个多样化分支，对研究人员来说非常有趣，因为被囊动物是现存与脊椎动物最接近的亲属，并且它们促进了我们自身生物学的比较研究。该群体还包括许多造成巨大经济损失的入侵物种，还有一些被囊动物是可食用的。尽管它们具有多样性和重要性，但被囊动物主要分支之间的关系尚未完全解决。在这里，我们补充了来自 7 个物种的转录组数据，这些物种涵盖了被囊动物的多样性，并对多达 798 个基因的数据集进行了系统基因组分析。我们采用了敏感性分析来检验减少组成异质性和分支长度异质性的影响。所有分析都最大程度地支持了 Olfactores（脊椎动物+被囊动物）内的单系被囊动物。在被囊动物中，所有分析都恢复了栉水母与被囊动物其余部分的姐妹关系，并（最大程度地支持）确认了尾索动物是内生于尾海鞘纲的。海鞘是所有其他被囊动物的姐妹分类群，除了栉水母。在大多数分析中，肠鳃纲被囊动物相对于无肠目是并系的。这种拓扑结构的支持程度不同，但在某些情况下是很强的。然而，当仅基于组成异质性分析前 50 个最佳基因时，我们恢复了肠鳃纲和无肠目是相互单系的，支持度很强，与大多数基于传统形态学的假说一致。对节段确定性的检查也对肠鳃纲并系的结果提出了质疑，这可能是由于分类群采样有限。总之，这些结果为我们最接近的现存无脊椎动物亲属提供了一个更高层次的系统发育框架。
