An analysis of genetic population structure in red drum, Sciaenops ocellatus, based on mtDNA control region sequences

Abstract

Genetic information per- taining to stock structure in red drum (Sciaenops ocellatus) is equivocal, com- plicating attempts to develop sound fishery management and stock enhance- ment plans. In this study, genetic stock structure was examined by using mito- chondrial DNA (mtDNA) control region sequences of 209 individual red drum from six locations in the Gulf of Mexico and five locations in the nearshore Atlantic Ocean off the southeastern United States. Eighty-one polymorphic sites within a 369 base-pair portion of the control region defined 134 dif- ferent haplotypes which differed by up to 26 nucleotide substitutions. Red drum showed high average within-sam- ple haplotype (0.98) and nucleotide (0.030) diversities. Sequence diver- gences between pairs of haplotypes ranged from 0.27% to 7.06% (x=3.17%). Cluster analysis of haplotypes revealed very little phylogeographic structure among mtDNA lineages. However, a neighbor-joining tree based on nucleo- tide divergence between pairs of sam- ples showed cohesion among Atlantic samples and, to a lesser degree, among Gulf samples. In contrast to a prior study, we found no evidence that red drum in Mosquito Lagoon, Florida, con- stitute a self-contained, reproductively isolated population. Hierarchical anal- ysis of molecular variance supported the hypothesis that red drum are subdi- vided into two weakly diverged popula- tions with a genetic transition in south Florida between Sarasota Bay and Mos- quito Lagoon. This area forms a zone of differentiation between two geneti- cally semi-isolated populations between which the structuring of heterogeneity differs from that under the assump- tion of panmixia. In addition, the analy- sis of molecular variance also indicated that red drum from Apalachicola Bay are genetically divergent from all other samples. The Atlantic and Gulf red drum populations are likely to respond independently to harvest regulations; these fisheries should continue to be managed separately. Additional subdi- vision of the Gulf stock between pen- insular Florida and the northern and western Gulf may also be warranted.