Dispersal and rapid evolution in brown trout colonizing virgin Subantarctic ecosystems

Two brown trout Salmo trutta stocks of different origin (wild Polish, domestic commercial) came into secondary contact after deliberate releases conducted in virgin rivers systems of the Subantarctic Kerguelen Islands (70 degrees E 49 degrees S). Samples obtained in 2001-2003 and a historical sample from 1993 were analysed for genetic variation at seven microsatellite loci and one allozyme locus (LDH-C1*). Bayesian clustering analysis demonstrated that rapid genetic differentiation formed separate genetic units in neighbouring rivers in less than 20 years. These genetic units were characterized by a large proportion of Polish genotypes mixed with some genomes of domestic origin (up to 30%). A different colonization strategy of the naturalized stocks, likely related with differential performance, was identified as a cause of rapid population differentiation in this area.