Abstract
Species with large geographic distributions often exhibit complex patterns of diversity that can be further complicated by human activities. Cutthroat trout (Oncorhynchus clarkii) are one of the most widely distributed freshwater fish species in western North America exhibiting substantial phenotypic and genetic variability; however, fish stocking practices have translocated populations outside of their native range and may have obscured intraspecific boundaries. This study focuses on cutthroat trout populations representing three distinct evolutionary clades that are found intermixed within a contact zone between the Bonneville and upper Snake River watersheds in the western United States. We used mitochondrial and microsatellite genetic data, as well as historical stocking records, to evaluate whether populations of cutthroat trout in the contact zone are native or are introduced. We found significant genetic differentiation and fine-scale genetic population structure that was organized primarily by watershed boundaries. While we detected increased genetic diversity in some areas in close proximity to the greatest number of stocking events, the highly organized population structure both within and between areas of the contact zone indicates that the populations are native to the watersheds. Intermixing of distinct evolutionary lineages of cutthroat trout appears to be the result of historical connections between paleodrainages. Our analyses provide a context for understanding how genetic data can be used to assess the status of populations as native or introduced.
Highlights
Natural geological processes may have a substantial influence on population structure and gene flow by altering the landscape through volcanism, glaciation, mountain building, and plate tectonics [1,2]
Over all cutthroat trout populations sampled for this study, 14 locations were in the Portneuf River watershed, 11 were in the Raft River watershed, and three were in the Malad River watershed (Table 1, Fig 1)
Of the 18 different haplotypes we detected in the contact zone, 15 haplotypes were identical to sequences previously deposited in Genbank; three new haplotypes were identified from One Mile Creek (H14), Second Creek (H16), and Pine Creek (H7; Table 2)
Summary
Natural geological processes may have a substantial influence on population structure and gene flow by altering the landscape through volcanism, glaciation, mountain building, and plate tectonics [1,2]. Habitat variability can lead to ecological specialization and genetic differentiation through behavioral, morphological, or physiological adaptation. Natural processes can sub-divide populations and promote diversification, human activities can obscure natural evolutionary patterns [4,5,6]. The translocation of species outside of their native range is arguably one of the most important human mediated factors that complicates native species distribution patterns [4,7,8,9]. For species with extensive geographic structuring, disentangling natural and human-mediated factors affecting their distribution can be difficult, but is critical to the development of management plans for protecting species and their role within ecosystems
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