Geographic Variation, Isolation, and Evolution of Cutthroat Trout with Comments on Future Directions for Management and Research
Dennis K. Shiozawa, R. Paul Evans, Derek D. Houston, and Peter J. Unmack
Abstract.—North American trout have undergone a long and complicated taxonomic history and this holds for taxonomic designations of Cutthroat Trout Oncorhynchus clarkii. Current Cutthroat Trout taxonomy recognizes a monophyletic species comprising 11–16 subspecies. The complex geological and climatic history of western North America is postulated to have strongly influenced differentiation among Cutthroat Trout subspecies. Early studies relied on morphological and meristic data in conjunction with fossil data and known aquatic connections within and among hydrological basins to infer the phylogenetic history of Cutthroat Trout. More recently, molecular studies incorporating karyotypes, allozymes, restriction fragment length polymorphisms, and mitochondrial DNA (mtDNA) sequence data have tested these early phylogenetic hypotheses and yielded additional insights into Cutthroat Trout evolution, although some phylogenetic relationships remain unresolved. In this study, we analyzed DNA sequence data from approximately half of the mitochondrial genome (8,057 base pairs) to better resolve phylogenetic relationships and estimate divergence times among Cutthroat Trout lineages. Herein, we present a well-resolved mtDNA phylogeny and discuss Cutthroat Trout evolution in a phylogeographic framework, as well as clarify current taxonomic implications and make recommendations for future research directions.