Evolution and Phylogenetic Significance of Ribosomal Gene Location in Chromosomes of Squamate Reptiles

Abstract

Using in situ hybridization with a biotin-labeled probe, we determined the chromosomal location of ribosomal genes in 56 species of squamate reptiles, including representatives of nine major taxa. Where possible, these data were examined in a phylogenetic context, and in several cases they provided phylogenetically useful shared derived character states. The ribosomal genes in Sceloporus variabilis are found on a single pair of microchromosomes, which seems to be primitive for the phrynosomatids. In the remainder of species of Sceloporus we examined, the ribosomal genes are found on the long arm of pair 2. We also found that Holbrookia, Cophosaurus, and Callisaurus share a derived condition not found in Uma. Two species of the viperid genus Agkistrodon share a condition that may be derived relative to other pit vipers. A third species of Agkistrodon differs from all other reptiles we examined in that ribosomal genes are located on the sex chromosomes. Location of rDNA also provides systematic information in several other clades of squamates.