Will there be a second extinction? Molecular identification of multiple alien water frogs (Pelophylax ridibundus sensu lato) in Tuscany, Central Italy, reveals genetic pollution within a unique hybridogenetic system

The introduction of alien water frogs is perhaps one of the most underestimated herpetological conservation issues in Europe. The identification of distinct species is highly challenging at the phenotypic level, and artificial syntopy between various taxa and lineages may lead to diverse outcomes, including hybridisation and local extinction. In central Italy the native synklepton of Pelophylax bergeri (the parental taxon) and P. kl. (klepton) hispanicus (the hybridogenetic hybrid, which clonally transmits the genome of an extinct ridibundus-like taxon) is present. Until recently, data regarding the presence of alien water frogs in central Italy was scarce, and no alien taxa have been reported for Tuscany. In this study, four distinct non-native Pelophylax lineages have been identified via molecular analysis in the Cecina and Arno river basins and ascribed to the Marsh frog group (P. ridibundus sensu lato). Alien Pelophylax ridibundus, P. kurtmuelleri, and P. cf. bedriagae sensu stricto currently appear to be widespread in the Cecina basin. Furthermore, evidence of hybridisation with autochthonous taxa has been suggested by genetic analyses in four out of eight sampling localities. With a view to evaluate urgent conservation strategies, a greater sampling effort is required to assess the actual distribution and ecology of the alien lineages, and further research is necessary to measure their impact on the native hybridogenetic system of the central-southern Italian pool frogs.