GENETIC DETECTION OF PUTATIVE HYBRIDIZATION BETWEEN NATIVE AND INTRODUCED RAINBOW-TROUT POPULATIONS OF THE UPPER SNAKE RIVER

Native trout populations throughout western North America have decline d because of habitat alteration, introgression with introduced trout, or competitive exclusion by nonnative species. Consequently, identific ation and preservation of native trout are now the goals of many manag ement programs. We examined allozyme and mitochondrial DNA (mtDNA) var iation in seven naturally occurring populations and one hatchery popul ation of rainbow trout Oncorhynchus mykiss from southern Idaho and nor thern Nevada to determine their genetic origins. Allozyme and mtDNA re sults were concordant in identifying three populations as genetically pure interior rainbow trout and one population as a hybrid swarm. Resu lts for the remaining four populations were discordant. However, these latter four populations were best classified as hybrid swarms due to the nature of either the allozyme or mtDNA data, which included geneti c characteristics of both coastal and interior rainbow trout. Our stud y demonstrates the utility of mtDNA analysis in conjunction with indep endent criteria such as allozymes for detecting hybridization at the p opulation level. Hybridized populations exhibited a greater number of mtDNA haplotypes than did genetically pure populations. Haplotypes wit hin hybridized populations differed more from one another than did mtD NA haplotypes within nonhybridized populations.