Molecular organization of 5S rDNAs in Rajidae (Chondrichthyes): Structural features and evolution of piscine 5S rRNA genes and nontranscribed intergenic spacers.

The genomic and gene organisation of 5S rDNA clusters have been extensively characterized in bony fish and eukaryotes, providing general issues for understanding the molecular evolution of this multigene DNA family. By contrast, the 5S rDNA features have been rarely investigated in cartilaginous fish (only three species). Here, we provide evidence for a dual 5S rDNA gene system in the Rajidae by sequence analysis of the coding region (5S) and adjacent nontranscribed spacer (NTS) in five Mediterranean species of rays (Rajidae), and in a large number of piscine taxa including lampreys and bony fish.

Rapid miocene-pliocene dispersal and evolution of Mediterranean rajid fauna as inferred by mitochondrial gene variation.

Rajidae (colloquially known as skates and rays) experienced multiple and parallel adaptive radiations allowing high species diversity and great differences of species composition between regional faunas. Nevertheless, they show considerable conservation of bio-ecological, morphological and reproductive traits. The evolutionary history and dispersal of North-east Atlantic and Mediterranean rajid fauna were investigated throughout the sequence analysis of the control region and 16S rDNA mitochondrial genes.