Mitochondrial DNA Diversity And Population Structure In Marine Fish Species From The Gulf Of Mexico
Variation in mitochondrial DNA (mtDNA) was examined among 693 red drum (Sciaenops ocellatus), 300 black drum (Pogonias cromis), and 421 red snapper (Lutjanus campechanus) sampled from several localities in the Gulf of Mexico. The number of mtDNA genotypes (haplotypes) observed were: 99 in red drum, 37 in black drum, and 68 in red snapper. Variation in mtDNA haplotype frequencies among localities in all three species was not significant, although two mtDNA haplotypes in black drum appeared to be clinally distributed. Maximum-parsimony analysis and phenetic clustering of mtDNA haplotypes and of samples in each species revealed little evidence of phylogeographic structuring. These data indicate that gene flow among localities in each species is sufficient to preclude genetic divergence. Spatial autocorrelation analysis of mtDNA haplotype frequencies revealed an isolation-by-distance effect in red drum and black drum, and indicated that migration between neighboring estuaries or bays in black drum may be less frequent than in red drum. Spatial autocorrelations in red snapper were negative in all distance classes, suggesting little migration even between adjacent localities. Differences in intrapopulational mtDNA diversities were found in all three species, suggesting that geographic differences in effective female population size may occur within each species.