Genetic assessment of native trout populations (Salmo trutta complex) in Lombardy (North Italy): implication for future conservation and management

The brown trout is a complex of developing species distributed around the Palearctic region. Glacial and interglacial peaks allowed the divergence of five main mitochondrial lineages. The reconstruction of its recent evolutionary history is essential to set-up concrete management and conservation efforts. Attempts to identify its native distribution is exacerbated by stocking activities with allochthonous strains during last century, which can lead to genetic introgression. An exhaustive genetic investigation has never been conducted in North Italy, especially in Lombardy region, which is posing critical management and conservation issues. In order to investigate the evolutionary status of trout in this area a genetic assessment of remote trout populations (possibly less impacted by introductions) was completed throughout the alpine and subalpine basins in Lombardy. For further strengthening, a few historical samples (back to 1821) collected in museums has been analysed. Genetic analyses covered more than 200 fish from 13 populations plus one population of hatchery-reared fish, used for stocking. Evolutionary history was inferred using the mitochondrial control region marker, whilst the level of introgression using the nuclear gene LDH-C1. Outputs revealed strong signs of introgression with the allochthonous strain. Nevertheless, the mitochondrial lineages linked to the Mediterranean brown trout is present in the current samples as well as in the museum samples, suggesting its historical presence in the ecosystems of alpine and subalpine basins.