A hotchpotch of water frogs in northern Italy

Water frogs of the genus Pelophylax have been widely traded by humans across all European countries for decades, and so far they have been shown to be invasive in most of them. The spread of alien Pelophylax threatens the persistence of native populations mainly via competition and hybridization. Particularly, the latter is worrying for the persistence of the native hybridogenetic systems, as it may induce hybrid swarms whose fnal outcome is hard to foresee. Alien water frogs have been already detected across several Italian regions, but the extension of the invasion is still unknown, in terms of both species composition and distribution. Here, we carried out the most extensive molecular survey of alien water frog populations across northern Italy, the main invaded area, and obtained a worrying scenario of multiple introduced alien taxa, often co-occurring at the same site. Frogs carrying the native mitochondrial haplotypes were found mainly at the edge of the invaded range. The most widespread taxa turned out to be P. ridibundus and P. kurtmuelleri, but members of the highly diversifed P. bedriagae species complex also occurred in the western (P. bedriagae) and the eastern sector (P. cf. bedriagae sensu stricto and P. cf. bedriagae “Cilician West”) of the range. We inferred the geographic origin of alien taxa according to mitochondrial haplotype variation and provide the fact-fnding background to investigate the impact of alien introductions on native populations, in order to evaluate efective and reliable conservation strategies for native hybridogenetic systems