Preliminary genetic data suggest the occurrence of the Balkan water frog, Pelophylax kurtmuelleri, in southwestern Poland

Recent molecular studies have detected the occurrence of exotic water frog species (Pelophylax sp.) in central and western European populations. Here, we report genetic evidence for the occurrence of the Balkan water frog, Pelophylax kurtmuelleri, in southwestern Poland. We found a high frequency of an allele of serum albumin intron-1 and a mitochondrial cytochrome b haplotype specific for this southern taxon in frogs from the Barycz river drainage system. We interpret this finding as evidence of admixture between P. kurtmuelleri and the local ridibundus-esculentus water frog population. The origin of the exotic P. kurtmuelleri mitochondrial and nuclear alleles in southwestern Poland could be due to (i) hybridization after a human-mediated introduction of P. kurtmuelleri, (ii) the persistence of ancestral polymorphism in central European P. ridibundus, or (iii) hybridization between P. kurtmuelleri and P. ridibundus in the Balkans followed by the northward expansion of admixed P. ridibundus. Identical mtDNA haplotypes found in southwestern Poland and localities on the borders between Greece, Albania and Macedonia suggest that this region harboured the source population of P. kurtmuelleri at the studied site.