Variation of sperm morphology in Pacific oyster precludes its use as a species marker but enables intraspecific geo-authentification and aquatic monitoring

According to recent reports, shell morphology is unreliable for the identification of oysters because of the high phenotypic plasticity of these bivalves. Using COI DNA barcoding and sperm morphology, we reinvestigated the species validity of wild Pacific oyster Crassostrea gigas habituating the Peter the Great Bay (Sea of Japan). DNA barcoding confirmed the species validity of samples collected. Application of the single sperm pattern was not possible for species identification due to pronounced sperm plasticity being found. Six sperm morphs were discovered in the testes of each oyster collected. The amount of abundant sperm morphs and the type of the most dominant sperm pattern are particular to geographical localities that are individual depending on the environmental factors. Ecological monitoring of marine areas and commercially assigned intraspecific geo-authentification of the Pacific oyster seems possible based on the analysis of this species’ heterogenic sperm. Further work will be needed to test if sperm heterogeneity exists in other Ostreidae species and if heterogenic sperms could be used for interspecific analysis.