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Detection of hybridization and introgression in wild populations that have been supplemented by hatchery fish is necessary during development of conservation and management strategies. Initially, allozyme data and more recently highly polymorphic microsatellite markers have been used to obtain this information. We used both markers to assess the effectiveness of four assignment methods (STRUCTURE, NEWHYBRIDS, BAPS and GeneClass) to detect hatchery introgression in wild stocked populations. Simulations of hybrid genotypes from real parental data revealed that the number and type of markers used with STRUCTURE, NEWHYBRIDS and BAPS can identify as admixed most first and second generation hybrids as well as first generation backcrosses. In wild populations, introgression rates estimated from different markers and methods were correlated. However, slight disagreements were observed at both population and individual levels. Overall, the fully Bayesian (STRUCTURE, NEWHYBRIDS and BAPS) performed better than partially Bayesian (GeneClass) assignment tests. In wild collections, BAPS analyses were limited because of the lack of a native baseline. In all cases, the efficiency of methods was reduced as introgression increased.

Compatible data from 11 polymorphic allozyme loci were assembled from 14 published studies and additional unpublished information for 232 native collections of brown trout sampled over a broad geographical range. Most of the genetic variation was explained by the distribution of allelic variation at the LDH-C* and CK-A1* loci. Patterns of geographical distribution coupled with postglacial geological events supported a model of colonization from three preglacial lineages, each fixed for different sets of alleles at these two loci. During glacial retreat, recolonization is proposed to have occurred mainly into adjacent areas through (i) a northwestern migration from an eastern Mediterranean-Caspian refuge, (ii) a northern expansion from a refuge in Atlantic drainages of Iberia and southern France, and (iii) a northern and eastern radiation from a refuge centred near the English Channel. Extant populations in deglaciated areas are suggested to represent mixed or pure descendants of these migrating groups. Repopulation from a fourth Mediterranean refuge distinguished by the presence of the LDH-A2*100QL allele was excluded based on the absence of this allele in repopulated areas.

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We provide mitochondrial sequence variation of the invasive fish Gambusiaholbrooki from 24 European populations, from Portugal to Greece. Phylogeographic structure in Europe was compared with genetic data from native samples (USA) and historical records were reviewed to identify introduction routes. Overall, data agree with records of historical introductions and translocations, and indicate that the most abundant haplotype throughout Europe originated from North Carolina and corresponded to the first introduction in 1921 to Spain, being transferred to Italy in 1922 and to many countries afterwards. Our results also show that at least another independent introduction occurred first in France and subsequently from France to Greece. Haplotypes of G. affinis were not detected in our European sampling effort but historical records and other data suggest that this species was introduced to Italy in 1927 and it might be present. At the continental scale, there is less diversity in Europe than in North America, in agreement with the low number of introduced fish. At the local scale, some European populations gained diversity from multiple introductions and from "de novo" mutationsThis study was financially supported by the Spanish Ministry of Education (CGL2006-11652-C02-02/BOS) and the Government of Catalonia (Catalan Government Distinction Award for University Research 2004 to EGB