A study of polymorphic microsatellite markers and mitochondrial DNA of pure and hybrid green frog populations of Rana spp

Abstract

Rana spp individuals were collected from three Serbian, one Montenegrian and two Greek localities and were scored for variation at their mitochondrial and nuclear genomes. Two regions of the mitochondrial genome, about 600 bp each, corresponding to the 16S rRNA and to cytb genes, were examined and six microsatellite loci were scored. The findings can be summarized as follows. 1. Three major phylads of mtDNA were found corresponding to previously described R. lessonae, R. ridibunda and R. epeirotica types. 2. Within the lessonae phylad we detected two distinct subclades, the standard lessonae and the lessonae U, the latter found so far only in the Ulcinj locality. 3. Within the epeirotica phylad, there are two subclades, one found in Ioannina and the other in Lysimachia. These subclades are less differentiated compared to the lessonae subclades. 4. One Serbian population, Nis, and one Greek population, Lysimachia, appear to consist mainly of one species, R. ridibunda and R. epeirotica, respectively. 5. The other four populations contain R. ridibunda in coexistence with a hybrid. In two Serbian and one Montenegrian populations the hybrid contains the genomes of R. ridibunda and R. lessonae, and is known as R. esculenta. In Ioannina the hybrid contains the genomes of R. ridibunda and R. epeirotica and is referred to here as “hybrid”. 6. The hybrids are hybridogenic, i.e. the produce eggs in which the whole set of chromosomes come from one parental species, this being R. lessonae in the Serbian populations and R. epeirotica in Ioannina. 7. In Pancevo and in Ioannina the hybrid male is inviable. 8. There is extensive heteroplasmy, but one in which one mtDNA is major and the other minor. This is a highly unusual situation and is reported for the first time in any animal population. We provide an explanation of this phenomenon based on: a) on the hybridogenic system of reproduction and, b) on the mechanism that prevents or allows leakage of paternal mtDNA in hybrids.