Phylogeographic inferences on the native brown trout mtDNA variation in central Italy

Italian Journal of Zoology (Impact Factor: 0.89). 06/2006; 73:179-189. DOI: 10.1080/11250000600679751

ABSTRACT Genetic diversity was analysed in Salmo trutta populations living in an area of central Italy by sequencing 310 bp of the 5′ end of the mtDNA control region (D‐loop) and by Restriction Fragment Length Polymorphism (RFLP) analysis of three mtDNA segments. Data show a genetic structure profoundly altered by stockings with allochthonous material of Atlantic origin. In fact, 15 of the RFLP haplotypes detected are linked to an Atlantic sequence. The remaining 9 were instead coupled with sequences representing the three major phylogenetic lineages previously identified in the Mediterranean basin (Adriatic, marmoratus, and Mediterranean), representing the native genetic diversity of brown trout in that area. The close genetic affinity observed between these latter haplotypes and those found in the Balkan peninsula by other authors seems to be in accordance with a recent, natural, history of dispersion between the two borders of the Adriatic Sea. These results appear significant from a conservation point of view as, in spite of the massive stocking with hatchery‐reared specimens, they highlight the persistence of Salmo trutta native genetic diversity in central Italy.

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    ABSTRACT: Brown trout Salmo trutta have been described in terms of five major mtDNA lineages, four of which correspond to major ocean basins, and one, according to some authors, to a distinct taxon, marbled trout Salmo marmoratus. The Atlantic and Danubian lineages of brown trout meet in a poorly documented contact zone in Central Europe. The natural versus human mediated origin of the Atlantic lineage in the upper Danube is a question of both theoretical and practical importance with respect to conservation management. We provide a comprehensive population genetic analysis of brown trout in the region with the aim of evaluating the geographic distribution and genetic integrity of these two lineages in and around their contact zone. Genetic screening of 114 populations of brown trout across the Danube/Rhine/Elbe catchments revealed a counter-intuitive phylogeographic structure with near fixation of the Atlantic lineage in the sampled portions of the Bavarian Danube. Along the Austrian Danube, phylogeographic informative markers revealed increasing percentages of Danube-specific alleles with downstream distance. Pure Danube lineage populations were restricted to peri-alpine isolates within previously glaciated regions. Both empirical data and simulated hybrid comparisons support that trout in non-glaciated regions north and northeast of the Alps have an admixed origin largely based on natural colonization. In contrast, the presence of Atlantic basin alleles south and southeast of the Alps stems from hatchery introductions and subsequent introgression. Despite extensive stocking of the Atlantic lineage, little evidence of first generation stocked fish or F1 hybrids were found implying that admixture has been established over time. A purely phylogeographic paradigm fails to describe the distribution of genetic lineages of Salmo in Central Europe. The distribution pattern of the Atlantic and Danube lineages is extremely difficult to explain without invoking very strong biological mechanisms.The peri-alpine distribution of relict populations of pure Danubian lineage brown trout implies that they colonized headwater river courses post-glacially ahead of the expansion of the Atlantic lineage. The recognition of natural as opposed to anthropogenic introgression of the Atlantic lineage into Danubian gene pools is of fundamental importance to management strategies.
    BMC Evolutionary Biology 08/2013; 13(1):176. · 3.29 Impact Factor
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    ABSTRACT: 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.
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