Lack of support for Deuterostomia prompts reinterpretation of the first Bilateria
Paschalia Kapli1, Paschalis Natsidis1, Daniel J. Leite1, Maximilian Fursman1,*, Nadia Jeffrie1, Imran A. Rahman2, Hervé Philippe3, Richard R. Copley4 and View Maximilian J. Telford1,†
Science Advances 19 Mar 2021:
Vol. 7, no. 12, eabe2741
Fig. 1 The deuterostome branch is short and weakly supported compared with the protostome branch.
Abstract
The bilaterally symmetric animals (Bilateria) are considered to comprise two monophyletic groups, Protostomia (Ecdysozoa and the Lophotrochozoa) and Deuterostomia (Chordata and the Xenambulacraria). Recent molecular phylogenetic studies have not consistently supported deuterostome monophyly. Here, we compare support for Protostomia and Deuterostomia using multiple, independent phylogenomic datasets. As expected, Protostomia is always strongly supported, especially by longer and higher-quality genes. Support for Deuterostomia, however, is always equivocal and barely higher than support for paraphyletic alternatives. Conditions that cause tree reconstruction errors—inadequate models, short internal branches, faster evolving genes, and unequal branch lengths—coincide with support for monophyletic deuterostomes. Simulation experiments show that support for Deuterostomia could be explained by systematic error. The branch between bilaterian and deuterostome common ancestors is, at best, very short, supporting the idea that the bilaterian ancestor may have been deuterostome-like. Our findings have important implications for the understanding of early animal evolution.
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