Genetic Similarity of Two Forms of Cutthroat Trout, Salmo clarki, in Wyoming

Patterns of genetic differentiation among populations of cutthroat trout, Salmo clarki, in fluvial and lacustrine habitats, as well as in an area where suspected subspecies occur sympatrically were studied using protein electrophoresis. Genetic variability is very low for two genetic parameters; the proportion of loci heterozygous per individual averaged 0.01, and the proportion of loci polymorphic per population averaged 0.05. These low values are attributed to the influence of recent glaciations. The genetic identity of populations is within a narrow spectrum of 1.00 to 0.995. An estimation of the time since divergence between the two morphological forms of cutthroat trout, based on the electrophoretic identity of proteins, is 20,000 years. These results support a hypothesis of a recent origin of the fine-spotted cutthroat trout within the Snake River drainage. MERISTIC analysis demonstrates only slight differentiation among subspecies of the polytypic cutthroat trout (Salmo clarki), yet often there are obvious differences in spotting pattern and body coloration (Roscoe, 1974). However because the spotting pattern and body coloration is so variable within, as well as between major drainages the origins and evolutionary relationships among the existing subspecies are poorly understood. One such confusing group is the cutthroat trout of the Snake River above Shoshone Falls and of the