Plitvice Lakes National park harbors ancient,yet endangered diversity of trout (genus Salmo)

National park Plitvice Lakes is the oldest, the largest and the most visited national park in Croatia, well known for its stunning karstic watersheds that supply Plitvice Lakes and exceptionally valuable biodiversity. Lack of knowledge on the taxonomic status, population structure and viability of trout in the Plitvice Lakes National park, as well as the possibility of existence of cryptic diversity, motivated this study which aimed to determine: taxonomic status and phylogenetic relationship of Plitvice Lakes trout with other Salmo species, genetic structure and diversity of their populations, as well as future viability of populations. 150 samples of trout were obtained from 17 localities. Two mitochondrial gene markers, gene for cytochrome b and mitochondrial control region were used in phylogenetic reconstruction, as well as in population genetic investigation. Intraspecific and intrapopulation genetic diversity was described by calculating several measures of genetic polymorphism, while gene flow among populations was estimated as the migration rates and as the number of immigrants per generation. Phylogenetic trees revealed that Plitvice Lakes watershed is inhabited by two evolutionary independent units of the genus Salmo, representing two species, Salmo labrax Pallas, 1814 and Salmo trutta Linnaeus, 1758. Possibly ‘pure’ populations of both species were found alongside several admixed ones in which both species are present. Our data has shown low intraspecific and intrapopulational diversities for Plitvice Lakes trout and restricted gene flow. Small effective sizes of populations and weak interconnections between them, which are most likely a consequence of fragmentation and habitat degradation, accentuating the need for urgent conservation measures.