GENETIC-RELATIONSHIPS AMONG GEOGRAPHICALLY ISOLATED POPULATIONS OF BLUEFISH (POMATOMUS SALTATRIX)

Restriction fragment length polymorphism (RFLP) analysis of mitochondr ial DNA (mtDNA) was employed to elucidate genetic relationships among six geographically isolated populations of bluefish (Pomatomus saltatr ix). MtDNA haplotypes based on nine informative restriction endonuclea ses were generated from samples of approximately 20 bluefish each from Portugal, Brazil, South Africa, western Australia and eastern Austral ia, and analysed with previous data for 472 bluefish from the east coa st of the USA and 19 from eastern Australia Considerable genetic varia tion was evident within most populations, with haplotype (nucleon) div ersities ranging from 0 . 104 to 0 . 924 (mean 0 . 686, pooled 0 . 917 ) and nucleon sequence diversities ranging from 0 . 05% to 0 . 71% (me an 0 . 42%, pooled 1 . 09%). No mtDNA haplotypes were shared among sam ples, although some haplotypes from isolated populations were quite Si milar, differing by one or two restriction site changes. Net nucleotid e sequence divergences between samples ranged from 0 . 26% (USA v. Por tugal) to. 1 . 75% (Brazil v. western Australia). Clustering of nucleo tide sequence divergences indicated that bluefish from the United Stat es, Portugal and South Africa were closely related, as were those from eastern and western Australia. The Brazilian sample was distantly rel ated to all other groups. Neighbour-joining and parsimony analyses of restriction site data supported the groupings based on nucleotide sequ ence divergences and suggested that a low degree of historical mixing may occur among closely related populations. Migration between isolate d populations, though very limited, could result from long-distance di spersal of early life-history stages or movements of vagile adults dur ing times of suitable temperate distributions.