Population structure, genetic diversity and demographic patterns unveil massive Mediterranean brown trout manipulations in a protected area of the northern Apennines (Italy)

Abstract The Salmo trutta species complex includes threatened or intensively managed taxa. Domestic-Atlantic strains are widely farmed and massively introduced into the wild to support fisheries, although such practices seriously threaten native populations of Mediterranean brown trout through anthropogenic hybridization. Characterizing the distribution and genetic composition of wild populations across river catchments is crucial to identify conservation priorities and define appropriate management strategies. Here, we genotyped 586 brown trout at the diagnostic nuclear LDH-C1 gene and the mitochondrial D-loop fragment, to assess the conservation status of 33 sites in a protected area spanning river catchments from both the Adriatic and Tyrrhenian slopes in the northern Apennines (Italy). The results indicated a critical situation of widespread domestic-Atlantic introgression. Further analyses at 15 microsatellite loci on 159 individuals from 12 natural sites (along with 113 references from hatcheries) revealed similarity to hatchery stocks, higher genetic diversity and bottleneck signals in introgressed/exotic populations, consistently with relatively recent introductions of domestic-Atlantic individuals into wild sites. Conversely, the only native sites from a single river catchment on the Adriatic slope showed genetic distinctiveness, reduced diversity and demographic stability. We also found genetic evidence of a human-mediated introduction of allochthonous Mediterranean trout in a single wild site, as well as of a putative between-slopes translocation. We provide further insight into the occurrence and consequences of human manipulations on wild Mediterranean brown trout populations, contextually offering a reliable baseline for an ongoing conservation project aiming at preserving native populations of this endangered taxon.