Geographic Patterns of Protein Variation and Subspeciation in Cutthroat Trout, Salmo clarki

Abstract

Genetic differentiation and the evolutionary relationships among 30 populations, representing five subspecies of inland cutthroat tout, Salmo clarki (Richardson), were studied by examining geographic variation at 35 genetic loci assayed with starch gel electrophoresis. Analysis of population subdivision using Nei's (1973, 1975) HT, HS, and GST statistics, indicated low genetic variability within, and extreme genetic subdivision among subspecies inhabiting independent basins and drainages. Substantial subdivision was also observed for isolated populations within the Labontan Basin. UPGMA and Wagner clustering analysis indicated that inland S. clarki can be subdivided into three major groups: 1) S. c. utah, S. c. pleuriticus, and S. c. bouvieri constitute a subspecies complex that inhabits drainages of the Bonneville Basin, Colorado River, Upper Snake River, and the Yellowstone River; 2) S. c. henshawi, a subspecies inhabiting the Lahontan Basin; and 3) S. c. lewisi, a widely dispersed group inhabiting the Upper Columbia and Upper Missouri River drainages. Salmo c. henshawi is closely related to the utah-pleuriticus-bouvieri complex whereas lewisi is electrophoretically distinct and not closely related to the other four inland subspecies. These results are concordant with chromosomal analysis and topographical changes in Western North America.