Genetic Variation in and Among Populations of Non-Native Brook Trout in Idaho: The Ghost of Introductions Past

How do founding populations of introduced species establish and invade when they should have reduced genetic variability, high extinction risk, and little adaptive potential?  Recent studies focusing on this “genetic paradox” have demonstrated that, in fact, invasive populations often have higher genetic variation than native populations and may possess pre-adapted or novel genotypes due to multiple introductions and in-situ hybridization among disparate native lineages.  Somewhat uniquely, fish have been introduced intentionally throughout the world, with local introductions often executed repeatedly and using mixtures of different strains from the native range – a context which may greatly influence invasive potential.  Here, we evaluate patterns of genetic diversity in non-native brook trout, which were introduced across the western US for over a century but have also invaded broadly and pose a primary threat to native trout species.  We analyzed 155 Single Nucleotide Polymorphisms (SNPs) identified in coding gene regions among 34 samples of brook trout populations across Idaho as well as samples from the only four strains documented to have been introduced in Idaho; the latter have a broad geographic origin ranging from Quebec to Pennsylvania.  We integrate our evaluation of population structure, population genetic diversity, and individual genotypic variation with assignments back to introduced strains to provide a genetic and historical context for this species’ ubiquitous invasive success.