Evolutionary Ecology of Redband Trout

We examined genetic differences at 29 enzyme encoding loci among 10,541 rainbow trout Oncorhynchus mykiss from 240 collections throughout the species’ range, including redband trout (i.e., several rainbow trout subspecies) in pluvial lake basins of the northern Great Basin that have had largely internal drainage with no connection to the Pacific Ocean. Differences among groups accounted for 29.2% of the genetic variation. Although we observed major genetic differences between coastal and inland groups (10.7%), which are currently considered to represent the major phylogenetic division in the species, we found that the greatest evolutionary divergence (19.7%) was related to persistence of three major river systems: the upper Sacramento, Klamath, and Columbia rivers. Genetic traits of redband trout from the northern Great Basin, where we found distinct subspecies or races, indicated that over millennia these pluvial habitats were sources of evolutionary diversity associated with large river systems rather than completely isolated refugia. However, redband trout did not constitute a distinct monophyletic group. Based on our data, redband trout of the Goose Lake, Warner Valley, and Chewaucan basins were distinct genetic races that were part of the diverse complex of Sacramento redband trout O. mykiss stonei. Harney Basin redband trout were a unique genetic race most closely associated with Columbia River redband trout O. mykiss gairdneri. White River and Fort Rock redband trout were associated with the Columbia River but showed allelic divergence comparable with that among other subspecies. Upper Klamath Lake rainbow trout included a previously unrecognized group associated with populations in the headwaters of the basin and a different subspecies from type locations for Upper Klamath Lake redband trout O. mykiss newberrii (i.e., Upper Klamath Lake and the upper Klamath River).