Nothing but a trace left? Autochthony and conservation status of Northern Adriatic Salmo trutta inferred from PCR multiplexing, mtDNA control region sequencing and microsatellite analysis

Phylogeny of Northern Adriatic Salmo trutta is still not resolved, leading to taxonomic controversies and hindering reasonable conservation and fisheries management. We report on the genetic screening of 467 brown trout from 25 sites within Adige, Brenta and Po River drainage basins (Italy). Our main aim was to identify native (Adriatic) brown trout within the central part of the Northern Adriatic area. D-loop lineage screening evidenced a predominance of the Atlantic clade with a frequency of 0.87, followed by the Marmoratus clade with 0.11, and, finally, the Adriatic clade with a frequency of 0.02. The Adriatic clade was found exclusively in specimens from Pianetti River and was represented by haplotype Adcs1. However, microsatellite-based analysis of population structure within Pianetti River specimens failed to identify Adriatic brown trout, but pointed to a nuclear genomic replacement of the former by Atlantic strains. In conjunction with earlier phylogenetic studies, our results contrast with a present-day widespread distribution scenario of Adriatic brown trout within the Northern Adriatic region. From a conservation viewpoint, the punctiform occurrence of Adriatic haplotypes, their ambiguous provenance, and, finally, the presumable genomic replacement at the nuclear genetic level, might hinder reasonable conservation actions and call for revised fisheries management guidelines.