INTROGRESSION OF THE FLORIDA LARGEMOUTH BASS GENOME INTO STREAM POPULATIONS OF NORTHERN LARGEMOUTH BASS IN OKLAHOMA

Oklahoma streams and reservoirs historically contained only the northe rn subspecies of largemouth bass Micropterus salmoides salmoides. From 1970 to 1991 Oklahoma reservoirs throughout the state were supplement ally stocked with the Florida subspecies M. s. floridanus and various intergrades of the northern and Florida subspecies. To document the ef fect of such introductions on the genetic structure of largemouth bass stream populations, largemouth bass throughout Oklahoma were sampled by seining. Electrophoretic analysis was carried out for loci that cod e the enzymes isocitrate dehydrogenase (sIDHP), aspartate aminotransfe rase (sAAT-B), and superoxide dismutase (sSOD). These three loci are d iagnostic for Florida largemouth bass. Analysis was also carried out f or loci that code the enzymes malate dehydrogenase (sMDH-A and sMDHB), phosphoglucomutase (PGM), and glucose-6-phosphate isomerase (GPI-A an d GPI-B). These five loci are known to be polymorphic in largemouth ba ss. Overall, Florida-subspecific alleles were found in 4% of fish coll ected and at 11% of sites that held largemouth bass. Combined frequenc ies of Florida-subspecific alleles ranged from 0.00 to 0.18; highest f requencies were in the southeastern half of Oklahoma. Overall genetic variability was highest among streams of the Red River basin, and sMDH -B was the most variable locus. Low mean F-st values (standardized va riances of allele frequencies) around 0.08 indicated little differenti ation among streams. Two distance matrices based on allele frequencies (one derived from the total data set and one from a subset that exclu ded individuals with Florida-subspecific alleles) showed significant c orrelation (approximate Mantel t-test, P < 0.0001). This indicated tha t the genetic relationships among all stream populations as a whole we re not significantly influenced by individuals with Florida-subspecifi c alleles. Allele frequencies that were not in Hardy-Weinberg equilibr ium (HWE) and heterozygote deficiencies at the sIDHP and sAAT-B* loci in introgressed populations suggested that the main influence of intr ogression was localized within individual stream systems. However, the finding of HWE in the population with the highest rate of introgressi on may have indicated a freely interbreeding mixture in that stream sy stem.