AN EVALUATION OF INTROGRESSION OF ATLANTIC COAST STRIPED BASS MITOCHONDRIAL-DNA IN A GULF-OF-MEXICO POPULATION USING FORMALIN-PRESERVED MUSEUM COLLECTIONS

Striped bass Morone saxatilis populations in drainages along the Gulf of Mexico coast (Gulf) were depleted in the 1950s and 1960s, probably because of anthropogenic influences. It is believed that only the Apal achicola-Chattahoochee-Flint (A-C-F) river system continually supporte d a naturally reproducing population of Gulf lineage. Striped bass juv eniles of Atlantic coast (Atlantic) ancestry were introduced to restor e population abundances in the A-C-F from the late 1960s to the mid 19 70s and in many other Gulf rivers from the 1960s to the present. We pr eviously identified mtDNA polymorphisms that were unique to approximat e to 60% of striped bass from the A-C-F and which confirmed the contin ued successful natural reproduction of striped bass of Gulf maternal a ncestry within the system. However, the genetic relatedness of the ext ant A-C-F population to 'pure' Gulf striped bass was not addressed. In this study, we determined the frequency of a diagnostic mtDNA XbaI po lymorphism in samples of 'pure' Gulf striped bass that were collected from the A-C-F prior to the introduction of Atlantic fish, that were o btained from museum collections, and that were originally preserved in formalin. PCR primers were developed that allowed for amplification o f a 191-bp mtDNA fragment that contained the diagnostic XbaI restricti on site. Using RFLP and direct sequence analyses of the PCR amplicons, we found no significant differences in mtDNA XbaI genotype frequencie s between the archived samples and extant A-C-F samples collected over a 15-year period. This indicates that significant maternally mediated introgression of Atlantic mtDNA genomes into the A-C-F gene pool has not occurred. Additionally, we found no evidence of the unique Gulf mt DNA genotype in striped bass from extant populations in Texas, Louisia na and the Mississippi River. These results highlight the importance o f the A-C-F as a repository of striped bass to restore extirpated Gulf populations and the potential use of museum collections in retrospect ive population studies.