Genetic Divergence and Effective Size among Lane Snapper in US Waters of the Western Atlantic Ocean

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Coastal Sciences, Gulf Coast Research Laboratory


Population structure of lane snapper Lutjanus synagris in U.S. waters in the northern Caribbean Sea was assessed using nuclear-encoded microsatellites and mitochondrial DNA (mtDNA) from samples from four localities in the U.S. Caribbean and one locality in the Florida Keys. Significant heterogeneity was detected for both allele and genotype distributions (microsatellites) and for haplotype distribution (mtDNA). Pairwise comparisons revealed that fish in the Florida Keys differed significantly from fish in the U.S. Caribbean with respect to both microsatellites and mtDNA. A parsimony network of mtDNA haplotypes was consistent with division of the five sample localities into two distinct populations. Genetic diversity at both microsatellites and mtDNA was greater among fish from the Florida Keys. The average, long-term migration rate from the U.S. Caribbean westward to the Florida Keys was approximately 1.75-fold greater than the reverse, suggesting that the elevated genetic variability among fish from the Florida Keys reflects the westward movement of alleles as a function of westward-flowing surface currents in the region. Bayesian coalescent analysis (microsatellites) indicated that each of the two populations has experienced a 10-fold decline in effective population size (Ne). Estimates of long-term effective size, generated using a coalescent, maximum-likelihood method, were 1,671.9 (Florida Keys) and 2,923.2 (U.S. Caribbean). Estimates of contemporaneous effective size, generated using a linkage-disequilibrium approach with minor alleles (those with frequencies of 0.02 or less) being excluded, were 275.6 (Florida Keys) and 668.9 (U.S. Caribbean) and differed significantly from one another. Because the samples contained mixed cohorts, the short-term estimates reflect the effective number of breeders (Nb) that produced the cohort(s) from which the samples were taken. The difference between the long-term and short-term estimates of Ne (or Nb) suggests that the declines in the effective size of both populations are relatively recent and that management concern over lane snapper in the Florida Keys is justified.

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North American Journal of Fisheries Management





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