GENETIC-STUDIES IN MARINE FISHES .4. AN ANALYSIS OF POPULATION-STRUCTURE IN THE RED DRUM (SCIAENOPS-OCELLATUS) USING MITOCHONDRIAL-DNA

Variation in mitochondrial DNA (mtDNA) was examined among 397 individuals representing 13 geographic samples of red drum (Sciaenops ocellatus). Five of the samples were from the Atlantic coast of the southeastern United States, and eight were from the northern Gulf of Mexico. Seventy-six mtDNA haplotypes were found: eight haplotypes were found in 13 or more individuals, ten were found in four to 12 individuals, 22 were found in two to three individuals, and 36 were found in only one individual each. Mitochondrial DNA nucleon diversity values within samples ranged from 0.850 to 1.000; the value over all fish surveyed was 0.943. These data indicate that red drum have at least "normal" levels of genetic variability. Estimates of the percentage nucleotide sequence divergence among the 76 mtDNA haplotypes ranged from 0.137 to 1.962, with a mean (+/- SE) of 0.803 +/- 0.006. Heterogeneity in the frequencies of four haplotypes was detected between pooled samples from the Atlantic vs. pooled samples from the Gulf. No heterogeneity was detected among samples from the Atlantic or among samples from the Gulf. F(ST) values (a measure of the variance in mtDNA haplotype frequencies) over the four heterogeneous haplotypes ranged from 0.019 to 0.137 (mean F(ST) = 0.057), and the effective number of female migrants (N(e)m) per generation using Wright's island model ranged from 1.58 to 12.91 (mean N(e)m = 4.14). The average percentage nucleotide sequence divergence within samples ranged from 0.494 to 0.734, with a mean (+/- SE) of 0.574 +/- 0.021. The percentage nucleotide sequence divergence among pairwise comparisons of samples ranged from 0.498 to 0.713, with a mean (+/- SE) of 0.571 +/- 0.005. Parsimony and phenetic analyses of individual mtDNA haplotypes and of sample localities revealed no strong evidence for geographic cohesion of haplotype or sample groupings. A matrix correlation (Mantel) test also revealed no significant association between matrices of mtDNA sequence divergence and geographic distance among sample localities. Collectively, these data indicate that the red drum population is weakly subdivided, with semi-isolated subpopulations occurring along the southeastern Atlantic coast and in the northern Gulf of Mexico. The large number of rare or unique mtDNA haplotypes found in the study may prove useful in evaluating the success of red drum stocking programs.