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 we re: 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 appea red to be clinally distributed. Maximum-parsimony analysis and pheneti c clustering of mtDNA haplotypes and of samples in each species reveal ed little evidence of phylogeographic structuring. These data indicate that gene flow among localities in each species is sufficient to prec lude genetic divergence. Spatial autocorrelation analysis of mtDNA hap lotype frequencies revealed an isolation-by-distance effect in red dru m and black drum, and indicated that migration between neighboring est uaries or bays in black drum may be less frequent than in, red drum. S patial autocorrelations in red snapper were negative in all distance c lasses, suggesting little migration even between adjacent localities. Differences in intrapopulational mtDNA diversities were found in all t hree species, suggesting that geographic differences in effective fema le population size may occur within each species.