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Open Access Publications from the University of California

Evolutionary Genetics of Rainbow Trout, Parasalmo gairdnerii (Richardson)


Starch-gel electrophoresis was used to obtain allozyme data from 114 populations of rainbow-series trout. Seventy-three alleles were segregating at 24 genetic loci. An additional seven loci were monomorphic in all populations. Eight genetically discrete intraspecific population-groups were identified and formal nomenclatural recognition of their subspecific status was suggested. The widespread coastal rainbow trout subspecies, Parasalmo gairdnerii gairdnerii was found to have higher levels of genetic variability than seen in most salmonid species. A substantial proportion, 86.8%, of the total heterozygosity was ascribed to within population variation. Between population genetic identity estimates were high and only weakly correlated with geographic proximity. Historical rates of gene flow among coastal rainbow trout populations was estimated to be high, at least 1.7 migrants per population per generation. Seven populations were distinguished by unique alleles, analysis of which indicate that these populations may have recently been isolated from other coastal rainbow trout populations.

A few headwater streams in Baja California del Norte' comprise the very restricted range of the San Pedro Martir trout. Closely related to but distinct from coastal rainbow trout, P. g. nelsoni are easily separated from all other Parasalmo taxa on the basis of a unique creatine kinase allele. In Northern California and Nevada, throughout the Pacific Northwest east of the Cascade Mountains are found redband trout, previously considered a single taxon defined by symplesiomorphic characters. Genetic data delineated three groups: inland redband trout, P. g. gibbsii; McCloud River redband trout, P.g. newberrii; and Goose Lake redband trout, P.G. ssp. Each redband trout was distinguished quantitatively by between taxa genetic distance estimates and qualitatively on the basis of characteristic alleles. Endemic to the Kern River basin are three rainbow-series trout taxa each diagnosed by characteristic alleles: Volcano Creek golden trout, P. g. aquabonita; Little Kern River golden trout, P. g. whitei; and Kern River rainbow trout, P. g. qilberti. Both golden trout taxa exhibited relative genetic paucity. Genetic evidence suggests a testable hypothesis of a hybrid origin for Kern River rainbow trout.

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