Coding Gene Single Nucleotide Polymorphism Population Genetics of Nonnative Brook Trout: The Ghost of Introductions Past

Abstract

Fish have been translocated throughout the world, and introductions often have been executed repeatedly and have used mixtures of different strains from the native range. This history might have contributed to their invasive potential by allowing introduced and invading populations to circumvent expected reductions in genetic diversity from founder effects in a scenario termed the “genetic paradox” of invasions. We characterize patterns of genetic diversity in nonnative Brook Trout Salvelinus fontinalis, which have been introduced across the western United States for over a century but have also invaded broadly and pose a primary threat to native trout. We analyzed 155 coding gene single nucleotide polymorphisms (SNPs) in 34 nonnative Brook Trout populations sampled across eight large river systems as well as samples from the only four hatchery strains with documented use in Idaho. We uncovered similar within-population genetic diversity and large effective population sizes in naturalized populations compared with hatchery samples. Naturalized populations also showed substantial genetic structuring (maximum pairwise F _ST = 0.23) across and even within watersheds and indicated suggestions of admixture in certain regions. Assignment probabilities confirmed two main hatcheries as the origin of most fish collected in the field; however, the four hatcheries were excluded as being the origin for 8% of individuals, mirroring results from clustering analyses and suggesting the influence of an additional unsampled hatchery source or sources. Simulated admixtures of hatchery samples produced genetic patterns similar to those observed in field samples, further supporting an influence of multiple historic hatchery stocks on the contemporary genetic structure of Brook Trout in Idaho. Our study highlights the potential contribution of historic hatchery and introduction practices in creating genetically variable and structured naturalized Brook Trout populations across Idaho, which may have allowed these fish to defy the “genetic paradox” early on in their nonnative history and set the stage for successful establishment and subsequent invasion.

Received September 4, 2012; accepted March 31, 2013

ACKNOWLEDGMENTS

This work was funded by Grant 2008-0087-000 of the National Fish and Wildlife Foundation's Keystone Initiative for Freshwater Fishes and is dedicated to the memory of Jim Sedell. We gratefully acknowledge the following people for providing us with genetic samples: Tom Curet and Brett High (IDFG), Mike Young and Aaron Prussian (U.S. Forest Service), Mike Liens (Friends of the Teton River), Jim DeRito (Henrys Fork Foundation), Jody White (Quantitative Consulting), Charlie Conklin (Paradise Brook Trout Company), John Fieroh (Brandon Enterprise Fisheries), and Ed Stege (Leadville National Fish Hatchery). Tom Frew, Liz Mamer, Sharon Clark, and Jeff Dillon of IDFG and Chris Kennedy of the LNFH provided information and documents on hatchery and fish stocking practices. We thank Dan Dauwalter, Seth Wenger, and Matt Mayfield (Trout Unlimited) for help with analyses and figures, and Bruce Rieman, Jason Dunham, Mike Young, and Kurt Fausch for informative discussions on this topic. We also thank A. Montpetit and A. Belisle from Génome Québec Innovation Centre (McGill University, Montreal) for their assistance in SNP genotyping. This manuscript was improved by comments from Jason Dunham, Dan Dauwalter, two anonymous reviewers, and the editor and associate editor of this journal.