Common pearl oysters in China, Japan, and Australia are conspecific: evidence from ITS sequences and AFLP

To elucidate the species status of Pinctada fucata in China, P. fucata martensii in Japan and P. imbricata in Australia, one population of each taxon was studied using internal transcribed spacer 1 and 2 (ITS1, and ITS2) and amplified fragment length polymorphism (AFLP) markers. ITS1 and ITS2 were 401-405 and 229-237 bp long, respectively. Twenty-nine ITS1 and 15 ITS2 unique genotypes were obtained from 44 and 34 individuals, respectively, with some genotypes shared by two or three populations. In AFLP analysis, each individual exhibited a distinct phenotype. No population had diagnostic markers. Mean genetic divergences within and among the three populations were very low and overlapped (between-population: 0.7-0.9% for ITS1, 0.9-1.3% for ITS2, and 53.3-55.6% for AFLP; within-population: 0.5-0.9% for ITS1, 0.8-1.2% for ITS2, and 50.4-53.6% for AFLP). Low levels of genetic differentiation were observed among the three populations while the Australian population is partially genetically isolated. Under an infinite allele model, genetic differentiation among populations was not significant based on a permutation test. Under an infinite site model, most F-ST values were not significant for ITS data although they were significant for AFLP data. Network analysis using ITS data indicated that individuals from the same population did not cluster together. Analysis of molecular variance (AMOVA) demonstrated that > 94% variation was contributed by within-population variation. These findings suggest that the three taxa are conspecific and Pinctada fucata is the correct name.