Introgression of the Florida Largemouth Bass Genome into Stream Populations of Northern Largemouth Bass in Oklahoma

Abstract

Oklahoma streams and reservoirs historically contained only the northern subspecies of largemouth bass Micropterus salmoides salmoides. From 1970 to 1991 Oklahoma reservoirs throughout the state were supplementally stocked with the Florida subspecies M. s. floridanus and various intergrades of the northern and Florida subspecies. To document the effect 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 code the enzymes isocitrate dehydrogenase (sIDHP), aspartate aminotransferase (sAAT‐B), and superoxide dismutase (sSOD). These three loci are diagnostic for Florida largemouth bass. Analysis was also carried out for loci that code the enzymes malate dehydrogenase (sMDH‐A and sMDH‐B), phosphoglucomutase (PGM), and glucose‐6‐phosphate isomerase (GPI‐A and GPI‐B). These five loci are known to be polymorphic in largemouth bass. Overall, Florida‐ subspecific alleles were found in 4% of fish collected and at 11 % of sites that held largemouth bass. Combined frequencies of Florida‐subspecific alleles ranged from 0.00 to 0.18; highest frequencies 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 Fst values (standardized variances of allele frequencies) around 0.08 indicated little differentiation among streams. Two distance matrices based on allele frequencies (one derived from the total data set and one from a subset that excluded individuals with Florida‐subspecific alleles) showed significant correlation (approximate Mantel t‐test, P < 0.0001). This indicated that the genetic relationships among all stream populations as a whole were not significantly influenced by individuals with Florida‐subspecific alleles. Allele frequencies that were not in Hardy–Weinberg equilibrium (HWE) and heterozygote deficiencies at the sIDHP* and sAAT‐B* loci in introgressed populations suggested that the main influence of introgression was localized within individual stream systems. However, the finding of HWE in the population with the highest rate of introgression may have indicated a freely interbreeding mixture in that stream system