Characterization of two repetitive DNA families (RrS1 and Rana/Pol III) inthe genomes of Palaearctic green water frogs

Two repetitive DNA families were detected in the genomes of Palaearctic gre en water frogs. The first family, named RrS1, is a centromeric satellite DN A, which allows discrimination between the genomes of Rana ridibunda and Ra na lessonae, thence representing a useful molecular tool to determine timin g and modes of genome exclusion from the germ line cells of the hybrid R, e sculenta. The second repetitive family, named Rana/Pol III, consists of sho rt, tandemly arrayed sequences, scattered throughout the genomes, and resem bling SINE retroposons in their structure. The Rana/Pol III family is prese nt in the genomes of R. lessonae, R. ridibunda, and their hybrid R. esculen ta, as well as in R. shqiperica, R. epeirotica, R. cretensis, and the Itali an taxon. These sequences are also present in the Iberian species R. perezi , although less abundant, but appear to be lacking in the North African spe cies R. saharica. The distribution of Rana/Pol III elements in the genomes of Palaearctic green water frogs is in agreement with the phyletic history of these anurans, on the basis of genetic data, and enables us to suppose t hat the hybridogenetic mechanism is one of the factors accounting for the p ossible horizontal transfer of transposable elements.