Population genetics reveal patterns of natural colonisation of an ecologically and commercially important invasive fish

Although historical records of introductions that trigger successful biological invasions are common, subsequent patterns of dispersal and colonisation mutes are unclear. We use microsatellites to examine genetic population structuring of established invasive brown trout (Sabno trutta) populations in Newfoundland, Canada for evidence of "natural" dispersal, human-mediated introductions, and colonisation routes. We also explored ancestry of contemporary populations relative to presumed progenitors. Results analysed using STRUCTURE, DAPC, a NJ tree and F-ST comparisons support records of historical introductions; current Newfoundland populations are largely descended from Scottish stock, with St. John's the primary introduction site. Subsequent dispersal of these trout was facilitated principally by anadromy, largely consistent with a classic stepping-stone model, with significant isolation-by-distance. With one exception, dispersal along the north and south coasts of the Avalon peninsula appears to be natural and independent, involving stochastic processes resulting in unique outcomes for population composition. This study is a good example of dispersal patterns during a contemporary invasion underscoring the potential for non-anadromous founders to re-express anadromy, facilitating colonization of distant sites.