GENETIC SUBDIVISION OF THE PEARL OYSTER PINCTADA-MAXIMA (JAMESON, 1901) (MOLLUSCA, PTERIIDAE) IN NORTHERN AUSTRALIA

The genetic structure of the pearl oyster Pinctada maxima in northern Australia was investigated by starch-gel electrophoresis. Six polymorphic enzymes were examined in 220 individuals from five areas which span a distance of 3400 km. Across this range, the average F(ST) is 0 . 104, with three of the loci showing highly significant variation in allelic frequencies. Most of the geographic variation is clinal between western and eastern populations. Particularly striking is the near substitution of alternate alleles for GOT between Western Australia and north-eastern Queensland. Comparisons between adjacent pairs of samples usually revealed significant genetic differences, including differences between two areas in the Northern Territory separated by 320 km. In contrast, two samples from Western Australia showed little evidence of genetic subdivision over a distance of more than 800 km. These genetic comparisons indicate that stocks of P. maxima are highly subdivided in northern Australia, but they also favour the view that there are substantial connections of Western Australian populations over large distances.