Introgression of Nuclear DNA (nDNA) Alleles of Stocked Atlantic Coast Striped Bass with the Last Remaining Native Gulf of Mexico Population

Abstract

AbstractSince the 1960s, only the Apalachicola–Chattahoochee–Flint (ACF) river system has continually supported a naturally reproducing population of striped bass Morone saxatilis of Gulf of Mexico (Gulf) lineage. Striped bass fry and fingerlings of Atlantic ancestry (from the Santee– Cooper system) were introduced into the ACF from the late 1960s to 1977. Genotypes were previously identified that were unique to fish from the ACF and that confirmed the continued natural reproduction of striped bass of Gulf ancestry within that population. Also, no significant difference in haplotype frequencies between “pure” archived ACF and extant ACF samples was found at an Xba I mitochondrial DNA (mtDNA) restriction site that is diagnostic in distinguishing extant ACF from extant Atlantic specimens. This suggested that significant maternally mediated introgression of Atlantic mtDNA genomes has not occurred. However, because mtDNA is maternally inherited, the introgression of paternally derived nuclear DNA alleles into the ACF gene pool was not evaluated. In this study, five microsatellite loci were identified that were diagnostic in distinguishing between extant Atlantic and ACF fish. The frequencies of diagnostic alleles at three of these loci were determined in archived scale samples of Gulf striped bass from the ACF and Atlantic fish from the St. Johns River along the Atlantic coast of Florida. Fixed differences in allelic identity were found between the archived collections at two loci and significant frequency differences at the third. Significant allelic frequency differences at all three loci were found between extant ACF samples collected over 8 years and the archived ACF collection. These were used to estimate that the degree of introgression of alleles of Santee–Cooper origin with the extant ACF population is 0.515. Despite the introgression of Atlantic alleles, management efforts to restore the ACF population are warranted because of continued successful natural reproduction and the substantial frequencies of unique Gulf alleles in its population.