Subspeciation in Cutthroat Trout Based on Geographic Patterns of Protein Variation

Electrophoretic procedures developed in the early to mid-1960s enabled researchers to rapidly and reliably identify allozyme variation reflecting simple Mendelian genetic differences between taxa.  Although subsequently used primarily for population genetics studies, allozyme data were soon recognized as having at least limited systematic value.  When applied to the Cutthroat Trouts, substantial genetic divergence was found between Behnke’s earlier-recognized Coastal and Westslope subspecies, a Lahontan Basin group, and a Yellowstone group consisting of Behnke’s Yellowstone, fine-spotted Snake River, Bonneville, Colorado River, Greenback, and Rio Grande subspecies.  Indeed, Nei’s genetic distance values for each of these four groups were as large as those delineating species-level separation in other taxa, but within the Lahontan group and within the Yellowstone group, little (sometimes no) genetic divergence was found.  Additionally, one study reported that the Lahontan group, albeit its substantial divergence, may be to be closer to the Yellowstone group genetically than to the Westslope or Coastal subspecies, which is consistent with their chromosome karyotypes; also trouts from Utah’s Sevier River drainage and from the Snake Valley streams along the Utah-Nevada border are more similar to the Colorado River subspecies than they are to Bear River populations in the Bonneville basin.