Microsatellite variation, effective population size, and population genetic structure of vermilion snapper, Rhomboplites aurorubens, off the southeastern USA

Vermilion snapper (Rhomboplites aurorubens) were collected from four sites off the Atlantic coast of the USA and one site in the Gulf of Mexico to eva luate effective population size and genetic stock structure. Previous studi es had suggested geographic variation in the ratio of males to females, so this population characteristic was explored in conjunction with the genetic analysis. Sex ratio varied greatly among the five sample sites; males comp rised 57% of samples in the Gulf of Mexico, while within the South Atlantic Eight they comprised between 36% (Morehead City, North Carolina) and 53% ( Carolina Beach, North Carolina) of samples. No clear geographic trends in t he sex ratio emerged; instead, it was found to vary with fish length, the p ercentage of males decreasing with increasing size. Allelic variation asses sed at seven dinucleotide microsatellite loci was large; gene diversities r anged from 0.43 to 0.95 and allelic counts from 7 to 39. Estimates of the e ffective population size ranged from 24 500 (based on the infinite-alleles model) to 150 500 (based on the stepwise-mutation model). There was evidenc e for excess homozygosity within samples: estimates of F-IS (the correlatio n of alleles within individuals) ranged from 0.01 to 0.03 among the seven l oci, and three estimates were significantly greater than zero. Differentiat ion among localities was very weak, as estimates of F-ST (the correlation o f alleles within populations) were on the order of 0.001 to 0.002 and genet ic distance estimates between localities were not related to geographic dis tances. This suggested that vermilion snapper in the South Atlantic Eight ( Cape Hatteras, North Carolina to Cape Canaveral, Florida) and Gulf of Mexic o are likely to consist of one genetic stock. Despite the overall homogenei ty, there were indications of a temporally dynamic local structure that wou ld bear further examination.