Is the deuterostome clade an artifact?

Area of Science:

• Evolutionary Biology
• Phylogenetics
• Animal Kingdom

Background:

• The clade Deuterostomia, comprising Chordata, Echinodermata, and Hemichordata, is a long-standing consensus in animal phylogeny.
• Recent phylogenetic analyses have cast doubt on the monophyly of Deuterostomia due to short branch lengths potentially indicating systematic error.

Purpose of the Study:

• To investigate potential sources of systematic error influencing phylogenetic analyses of Deuterostomia.
• To re-evaluate the monophyly of Deuterostomia by employing a site-by-site approach and mitigating known sources of error.

Main Methods:

• Utilized a site-by-site phylogenetic analysis approach.
• Simulated conditions promoting long-branch attraction (LBA), such as branch-length heterogeneity and amino acid compositional constraints.
• Implemented methods to mitigate potential systematic errors in phylogenetic inference.

Main Results:

• Deuterostome monophyly was strongly supported under conditions that promote long-branch attraction (LBA).
• Mitigation of LBA-promoting factors led to a marked decrease or disappearance of support for Deuterostomia.
• The findings suggest that previous support for Deuterostomia may be an artifact of systematic error.

Conclusions:

• The monophyly of Deuterostomia, a cornerstone of animal phylogeny, is questionable when systematic errors are accounted for.
• A very short or non-existent deuterostome branch has significant implications for interpreting early animal evolution, including fossil records and the nature of the bilaterian ancestor.