Genetic Relationships among Geographically Isolated Populations of Bluefish (Pomatomus saltatrix)

Abstract

Restriction fragment length polymorphism (RFLP) analysis of mitochondrial DNA (mtDNA) was employed to elucidate genetic relationships among six geographically isolated populations of bluefish (Pomatomus saltatrix). MtDNA haplotypes based on nine informative restriction endonucleases were generated from samples of approximately 20 bluefish each from Portugal, Brazil, South Africa, western Australia and eastern Australia, and analysed with previous data for 472 bluefish from the east coast of the USA and 19 from eastern Australia. Considerable genetic variation was evident within most populations, with haplotype (nucleon) diversities ranging from 0.104 to 0.924 (mean 0.686, pooled 0.917) and nucleon sequence diversities ranging from 0.05% to 0.71% (mean 0.42%, pooled 1.09%). No mtDNA haplotypes were shared among samples, although some haplotypes from isolated populations were quite similar, differing by one or two restriction site changes. Net nucleotide sequence divergences between samples ranged from 0.26% (USA v. Portugal) to 1.75% (Brazil v. western Australia). Clustering of nucleotide sequence divergences indicated that bluefish from the United States, Portugal and South Africa were closely related, as were those from eastern and western Australia. The Brazilian sample was distantly related to all other groups. Neighbour-joining and parsimony analyses of restriction site data supported the groupings based on nucleotide sequence divergences and suggested that a low degree of historical mixing may occur among closely related populations. Migration between isolated populations, though very limited, could result from long-distance dispersal of early life-history stages or movements of vagile adults during times of suitable temperate distributions.