Genetic discrimination of morphologically similar, sympatric species of pearl oysters (Mollusca : Bivalvia : Pinctada) in eastern Australia

Two species of small pearl oysters have long been recorded from New South Wales but these have proved difficult to separate on the basis of shell characters. An electrophoretic and morphological study has confirmed the presence of two genetic species. Four loci (of fourteen scored) show little overlap in the suite of allozymes present in the two species. There is a very low incidence of heterozygotes of taxon-characteristic allozymes at these loci, indicating that interbreeding between the species is infrequent. There is broad local sympatry of the species, with both occurring in all but one of the sites sampled on the eastern seaboard. The two species differ on average in several morphological ratios, but there is overlap in the ranges of all ratios. The more common species is genetically similar to three samples of P. imbricata (= P. radiata, P. fucata) from Japan (Nei unbiased distance of less than 0.08). There has been no previous indication of genetic subdivision within this species, so we regard the Japanese and Australian taxa as conspecific. The second species has been referred to P. albina and P. sugillata. We treat it as P. albina. Both taxa treated here are morphologically distinct from other similar small Pinctada species such as P. chemnitzi and P. maculata.