Allozyme and Morphological Divergence of Rainbow Trout (Oncorhynchus mykiss) above and below Waterfalls in the Deschutes River, Oregon

Abstract

We examined allozyme and morphological variation among populations of rainbow trout (Oncorhynchus mykiss) in the Deschutes River Basin. Populations isolated above a major waterfall in the White River (a tributary of the Deschutes River) represented a group of rainbow trout with plesiomorphic characteristics previously known only from isolated drainages of the northern Great Basin. White River populations were characterized by little or no variation at sSod-1 and Ldh-B2, fine scales, and few pyloric ceca. Other populations in the Deschutes River were more similar to anadromous populations east of the Cascade Mountains in the Columbia River. Our results suggest that the two forms in the Deschutes River and a persistent population in a desiccating drainage of the Great Basin in Oregon diverged from a common, ancestral population during the Pleistocene. We found no evidence that all isolated groups of rainbow trout with plesiomorphic characteristics in the White River, Oregon desert basins, and northern California represented a monophyletic group.