Use of high-resolution melting analysis for detecting hybrids between the oysters Crassostrea sikamea and C-angulata reveals bidirectional gametic compatibility

To the best of our knowledge, the hybridization potential between the two closely related oyster species, Crassostrea sikamea and C. angulata, has yet to be reported. Moreover, hybrids obtained in most early experiments on oyster hybridization have been inadequately validated by genetic methods. In this study, a novel method based on high-resolution melting (HRM) analysis was used to visualize the coexistence of species-specific single nucleotide polymorphisms or insertion-deletion variations from both oyster species. Mitochondrial cytochrome c oxidase subunit I sequences were used to track the genetic material from a female to its descendants, while the nuclear genomic sequences of the first ribosomal internal transcribed spacer regions were used to track the genetic material from both parents and confirm hybrids of C. sikamea and C. angulata. Based on HRM analysis, bidirectional gametic compatibility between C. angulata and C. sikamea was successfully detected, although only several hundreds of larvae successfully hatched from tens of millions of C. angulata eggs inseminated by C. sikamea sperm, and the larvae were inviable. These results suggest the existence of bidirectional gametic compatibility between C. angulata and C. sikamea. Hybrids from C. sikamea eggs and C. angulata sperm showed higher growth rates and survival success during the swimming-larva stage, and may be potentially used for the genetic improvement of oyster aquaculture. This study provides a useful and reliable method for confirming hybrids in samples from either laboratory research or ecological field studies.