Evolution of ribosomal internal transcribed spacers in Deuterostomia

[Display omitted] •Complete ITS1 and ITS2 sequences were analyzed in Deuterostomia 16 classes.•Length and GC-content increase in ITSs from primitive to higher Deuterostomia taxa.•Thymine content decrease in ITSs sense DNA sequences in the higher Deuterostomia.•Non-LTR retrotransposon insertion into the ITS1 of Geochelone nigra is detected.•Role of GC-biased gene conversion for Deuterostomia ITSs evolution is suggested. Sequences of ribosomal internal transcribed spacers (ITSs) are of great importance to molecular phylogenetics and DNA barcoding, but remain unstudied in some large taxa of Deuterostomia. We have analyzed complete ITS1 and ITS2 sequences in 62 species from 16 Deuterostomia classes, with ITS sequences in 24 species from 11 classes initially obtained using unannotated contigs and raw read sequences. A general tendency for both ITS length and GC-content increase from interior to superior Deuterostomia taxa, a uniform GC-content in both ITSs within the same species, thymine content decrease in sense DNA sequences of both ITSs are shown. A possible role of GC-based gene conversion in Deuterostomia ITS evolutionary changes is hypothesized. The first example of non-LTR retrotransposon insertion into ITS sequence in Deuterostomia is described in turtle Geochelone nigra. The roles of mobile genetic element insertions in the evolution of ITS sequences in some Sauropsida taxa are discussed as well.