Natural hybridization between Pinctada fucata and Pinctada maculata inferred from internal transcribed spacer regions of nuclear ribosomal RNA genes

Abstract

Genetic evidence of the occurrence of natural hybridization between female Pinctada fucata and male Pinctada maculata among wild pearl oysters (n=20) collected for use as the mother shell for private pearl farming in the Oshima Strait at Amami-o-shima, Kagoshima Prefecture, Japan, were obtained. A polymerase chain reaction-based species identification method for Pinctada was developed using polymorphisms in the internal transcribed spacer (ITS) region of the nuclear ribosomal RNA (rRNA) gene. This method enabled the amplification of the ITS regions using a primer set specific for P. maculata and P. fucata. However, 10 of 20 individuals morphologically identified as P. fucata had sequences specific to both P. maculata and P. fucata inthe ITS region. These putative hybrids showed sequences of a maternally inherited mitochondrial 16S rRNA gene, identical to that of P. fucata. Shells of the putative hybrids were difficult to discriminate from those of P. fucata exhibiting similar taxonomic traits. Moreover, the hybrids exhibited slower growth than P. fucata but faster growth than P. maculata.