MITOCHONDRIAL-DNA DIVERSITY OF ROANOKE RIVER STRIPED BASS

The genetic heterogeneity of mitochondrial DNA (mtDNA) in Roanoke River striped bass Morone saxatilis was examined by restriction endonuclease analysis of mtDNA isolated from 32 specimens captured during the 1989 and 1990 spawning runs. Restriction fragment banding patterns based on restriction site polymorphisms revealed six distinct genotypes, designated I-VI, among the 32 sampled individuals. The predominant genotype, designated genotype I, was found in 59% of the individuals sampled, while genotypes defined by Acc I-Nde I (genotype II), Taq I (genotype III), Taq I-Hinf I (genotype IV), Dde I (genotype V), and Spe I (genotype VI) were found in 25%, 7%, 3%, 3%, and 3% of the individuals. Five distinct mtDNA fragment length variants, designated classes A-E, were identified from the same 32 individuals. The number and size of individual length variants agreed with those identified previously in striped bass populations from geographically distant sites. Analysis of the distribution of length variant classes A-E among genotypes I-VI (defined by restriction site polymorphisms) revealed a lack of concordance between individual length variants and specific genotypes. Geographically and genotypically independent distributions of the five length variants strongly suggest that mtDNA fragment length variants have converged in striped bass. Although mtDNA fragment length variants have been used to distinguish among regional striped bass stocks, our results suggest that caution should be exercised in phylogeographic assignment on the basis of mtDNA length variants alone. Using estimates based on restriction site polymorphisms only, we calculated a nucleotide sequence divergence value of p = 0.003, nearly an order of magnitude greater than reported previously for striped bass. Our results indicate that either the Roanoke River striped bass stock is genetically more diverse than other striped bass stocks, or that previous estimates of stock diversity are low.