Evolution of the 28S ribosomal RNA gene in anurans: regions of variability and their phylogenetic implications

Fifteen restriction sites were mapped to the 28S ribosomal RNA gene ofindividuals representing 54 species of frogs, two species of salamanders, acaecilian, and a lungfish. Eight of these sites were present in all speciesexamined, and two were found in all but one species. Alignment of theseconserved restriction sites revealed, among anuran 28S rRNA genes, fiveregions of major length variation that correspond to four of 12 previouslyidentified divergent domains of this gene. One of the divergent domains(DD8) consists of two regions of length variation separated by a shortsegment that is conserved at least throughout tetrapods. Most of theinsertions, deletions, and restriction-site variations identified in the28S gene will require sequence-level analysis for a detailed reconstructionof their history. However, an insertion in DD9 that is coextensive withfrogs in the suborder Neobatrachia, a BstEII site that is limited torepresentatives of two leptodactylid subfamilies, and a deletion in DD10that is found only in three ranoid genera are probably synapomorphies.