Mitochondrial DNA diversity among populations of striped bass in the southeastern United States

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Abstract
Mitochondrial DNA (mtDNA) genotypes were determined for Atlantic striped bass from the St. Johns River in northeastern Florida and several hatchery reared individuals from Monck's Corner, South Carolina. Adults and hatchery-reared descendants of striped bass with high lateral line scale counts were sampled from several sites in the Apalachicola River system along the Gulf coast of Florida. In addition, naturally reproduced 1985 year class juveniles from the Apalachicola system were sampled. All mtDNA genotypes were compared with those observed in our sample of approximately 200 fish from the Atlantic coastal migratory stock. Ten different restriction endonucleases were used, generating 169 mtDNA fragments in most individuals. Heteroplasmy was observed in striped bass from both the St. Johns River and the Apalachicola system. Base sequence divergence among the populations surveyed was extremely low (maximum p = 0.0004), among the lowest reported for any animal species to date. However, the restriction enzymes RsaI and XbaI both revealed base substitutions unique to populations of Gulf Coast striped bass. Approximately 57% of striped bass from the Apalachicola system displayed an XbaI genotype not seen in any of our Atlantic collections. Four discrete mtDNA size classes were detected, differing by approximately 200, 300, and 400 base pairs from the smallest mtDNA molecule observed. The largest genotype was only seen in the Apalachicola system. The smallest genotype, while restricted to Gulf Coast striped bass sampled for this study, has been frequently observed in the Atlantic coastal migratory stock. The presence of mtDNA genotypes unique to the Apalachicola systems suggests the continued existence of a maternal lineage of striped bass of Gulf ancestry and points to the use of mtDNA as a valuable tag in the management of these populations. The lack of mtDNA sequence divergence in striped bass suggests a very recent origin for these populations.