Molecular characterization and hybridization in Salmo (trutta) macrostigma morphotypes from Central Italy

The super-species Salmo trutta is taxonomically divided into a number of semi-species, local varieties, morphs, and possible hybrids due to restocking. Their genetic status is nevertheless not always clear, although relevant for management and conservation practices. We used mitochondrial haplotypes, nuclear microsatellites, and LDH-C1 genotyping to study the trout population of Lake Posta Fibreno, one of the few extant populations of the semi-species Salmo (trutta) macrostigma (S.t.m.). Levels of introgression from Northern European stocks were estimated and the possible genetic separation and/or differential introgression were evaluated in the three generally recognized morphological variants fibreno, leopardo, and rossa. We show that trout from Posta Fibreno belong to the Adriatic group. The three morphotypes are genetically uniform, regardless of their apparently stable morphological differences. Low levels of introgression from non-autochthonous stocks of Northern European origin were detected, but these figures are not statistically different among the three morphs, ruling out the possibility that one or more morphs are in fact hybrid phenotypes. The relative purity of the S.t.m. population form Posta Fibreno was compared with available accounts of introgression in other Italian populations, showing that it is in fact one of the least affected, and of significant interest for conservation.