Far from Home: Tracing the non-native origin of water frogs (genus Pelophylax) in Malta by molecular markers

Abstract One of the most frequently translocated species outside their native range in Europe are water frogs of the genus Pelophylax. Recently, water frogs belonging to the same genus have also been recorded on the island of Gozo in Malta. To trace their origin, we genetically examined 17 individuals from three Gozitan localities where water frogs have been recorded recently. We analysed one mitochondrial gene (ND2) and one nuclear (SAI-1) gene to identify the geographic origin of the frogs and a set of microsatellite markers to determine their population-genetic structure and the predicted number of source populations. Based on the ND2 and SAI-1 markers, the water frogs on the island of Gozo originate from southern Anatolia, Turkey. According to sequence variation in ND2, they were assigned to a caralitanus mtDNA clade, which is endemic to southern Anatolia and taxonomically represents either an evolutionary lineage within P. cf. bedriagae or a separate species P. caralitanus. All Gozo water frogs had only one haplotype in the ND2 and one allele in the SAI-1 gene, indicating a recent and single introduction event. These results are supported by microsatellite analysis, which revealed low genetic variability and the absence of any population-genetic structure, suggesting that Gozo water frogs originate from only one source population.