Genetic Divergence and Effective Size among Lane Snapper in U.S. Waters of the Western Atlantic Ocean

Abstract

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 (N_e ). 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 (N_b ) that produced the cohort(s) from which the samples were taken. The difference between the long-term and short-term estimates of N_e (or N_b ) 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.

Received July 23, 2010; accepted December 14, 2010

ACKNOWLEDGMENTS

We thank the following people for their invaluable assistance in obtaining samples for this study: L. Anibal, J. Leon, H. Lopez, D. Matos-Caraballo, and A. Rosario of the Department of Natural and Environmental Resources Fisheries Research Laboratory in Mayaguez, Puerto Rico; W. Ledee and D. Olsen of the St. Thomas Fisherman's Association; H. Rivera and W. Tobias of the U.S. Virgin Islands Division of Fish and Wildlife; and R. Beaver of the Florida Fish and Wildlife Commission. We also thank E. Carson for generating Figure 1 and for constructive comments on a draft of the manuscript. This work was supported by the Cooperative Research Program of the U.S. Department of Commerce (Grant NA06NMF4540061) and Texas AgriLife Research Project H-6703. This article is number 75 in the series Genetic Studies in Marine Fishes and contribution 193 of the Center for Biosystematics and Biodiversity at Texas A&M University.