A chromosomal study of the Pyrenean endemic brown frog species, Rana pyrenaica, and various Italian populations of R-dalmatina and R-italica

This paper reports the data of a chromosomal analysis carried out by standa rd and banding stainings (C, Ag-NOR, Alu I, Chromornycine A(3)) in R. pyren aica. This Pyrenean endemic brown frog showed a 2n = 26 all biarmed chromos omes, settling in 5 large pairs + 8 relatively smaller pairs and NORs on th e short arm of the 6(th) chromosome pair. C-bands were observed in the NOR- associated regions and along the centromeres of all the chromosomes. Faint pericentromeric C-bands were also observed on the short arm of chromosomes 1 to 5. NORs localization and C-banding pattern are distinctive for this sp ecies. In fact, parallel analysis performed on specimens of different popul ations of R. italica and R. dalmatina, showed that heteromorphism for NORs and heterochromatin was restricted to size variation between homologues. Fu rthermore. chromosomes of R. dalmatina and R. italica showed a marked bias to no-nrandom gaps and/or ruptures after "in vitro" exposure to chemical st ress, offering a new insight into chromosomal differentiation and speciatio n in this species group via environmental stress- induced rearrangements.