Y Chromosome Marker Evolution in Cutthroat Trout
Gary H. Thorgaard, Joseph P. Brunelli, Nolan R. Smith, and Bobbi M. Johnson
Abstract.—A Y chromosome marker shared with Rainbow Trout Oncorhynchus mykiss has been sequenced in many Cutthroat Trout O. clarkii subspecies. The marker is found in and inherited through males. It evolves more slowly than the maternally inherited mitochondrial DNA. The marker delineates the four major groups of Cutthroat Trout: the Lahontan Cutthroat Trout O. c. henshawi subspecies complex, the Yellowstone Cutthroat Trout O. c. bouvieri subspecies complex, Westslope Cutthroat Trout O. c. lewisi, and Coastal Cutthroat Trout O. c. clarkii. The paternal inheritance pattern of the Y marker makes it useful for dissecting the origins of fish with mixed ancestries. We describe a case study using both Y and mitochondrial markers in Lahontan Cutthroat Trout subspecies complex trout populations. Our results confirmed Lahontan Cutthroat Trout affinities for the Paiute Cutthroat Trout O. c. seleniris and Willow–Whitehorse Creek Cutthroat Trout. However, we found evidence of a complex ancestry for Guano Creek, Oregon trout, a group that has been proposed by some to be related to the Alvord Cutthroat Trout, a subspecies thought to be extinct.