Introgressive hybridization between native and non-native smallmouth bass in Oklahoma

Scope and method of study. A genetic survey across the natural range of smallmouth bass, Micropterus dolomieu, demonstrated that the native populations in eastern Oklahoma represent the two most divergent lineages of the species (referred to as the Ouachita and Neosho smallmouth basses). These results generated a need for knowledge regarding the genetic structure of smallmouth bass in reservoirs within the native range that had been stocked with non-native Tennessee "lake strain" smallmouth bass. Microsatellite DNA loci were used to assess the genetic structure of smallmouth bass populations in two such reservoirs (Broken Bow and Tenkiller) and to test for genetic introgression of the native forms in upstream tributary populations.; Findings and conclusions. I identified and screened 14 microsatellite loci, three of which (Mdo1, Mdo2, and Mdo3) were diagnostic of the hatchery stock of the Tennessee lake strain within the range of the Ouachita smallmouth bass in Oklahoma and one of which (Mdo1) was diagnostic of the hatchery stock within the range of the Neosho smallmouth bass. Two of these three loci were diagnostically different between Oklahoma populations of the two native stocks, and the third locus showed marked differences in allele frequencies. The results indicated that alleles diagnostic of the Tennessee lake strain represent 41% of the genome in samples from Broken Bow Reservoir and 85--90% of the genome in samples from Tenkiller Reservoir. An analysis of growth versus genotype in the two reservoirs was precluded because the Broken Bow sample consisted almost entirely of backcross progeny and the Tenkiller sample consisted primarily of non-native genotypes for the locus examined. However, in both reservoirs, the marked change in genetic structure coincided with an apparent increase in the smallmouth bass fishery, indicating that the introduction of the Tennessee lake strain stimulated increased production of smallmouth bass. Samples collected in 1999, six to eight years after the introductions, showed no evidence of genetic introgression. However, the persistent occurrence of a reservoir population harboring non-native alleles means that, with time, genetic introgression of stream populations is likely to occur. Such introgression represents losses of native stocks and the management options they represent, and, in theory, could adversely affect the smallmouth bass fishery in streams.