Brown trout (<Emphasis Type="Italic">Salmo trutta</Emphasis>) invasiveness: plasticity in life-history is more important than genetic variability

Brown trout of German origin were introduced into Patagonian National Parks in 1905, where they acclimatized and underwent population expansion endangering populations of native species like Galaxiidae. Spawning adults of two populations were sampled in 2004. Their age, length-at-age and migratory behaviour were assessed from scale samples, as well as their variation at the coding LDH-C1* and eight non coding microsatellite loci. Between-population differentiation for life history (spawning time, migratory behaviour, length and weight at age) and reduced genetic variation were revealed. Based on genetic variation, effective population size smaller than 50 individuals has been estimated for the founder stock, and its German origin has been genetically traced. Flexibility in migratory behaviour and spawning time were identified as key factors conferring competitive advantage on those brown trout populations.