TAXON COMPOSITION AND GENETIC-VARIATION OF WATER FROGS IN THE MID-RHONE FLOODPLAIN

Natural hemiclonal hybrid lineages of water frogs reproduce by hybrido genesis, excluding one parental genome in the germ line and mating wit h the coexisting same parental species. Two such sexual host-hybridoge n system occur in the Rhone valley: the L-E system in the north, the P -G system in the south. Although these hybridogenetic complexes may ov erlap along the Rhone river, there is no evidence for a contact zone i n our samples: only Rana ridibunda and R. esculenta were identified us ing protein electrophoresis. Whether the absence of R. perezi reflects a more southern distribution or its exclusive occurrence in other hab itats, remains to be tested. Comparison of somatic and gonadal tissues reveals that gametogenesis of R. esculenta is of the L-E type: gamete s carry ridibunda genomes. R. ridibunda apparently is not native, but was introduced by humans, and the R. esculenta in our samples is proba bly an immigrant from nearby L-E systems.