Deciphering Production Potential and Gonadal Differentiation of the Backcross Hybrids Between Argopecten irradians and A. purpuratus

The scallops of the genus Argopecten hold a significant position in the international shellfish aquaculture industry. However, due to their hermaphroditic nature, selfing reproduction has led to an increasingly severe phenomenon of germplasm degradation. The development of interspecific hybridization can effectively address this issue, but the fertility of interspecific hybrid offspring is greatly affected. Backcrossing appears to be a more practical and feasible solution, yet current research in this regard remains extremely scarce. In this study, the F1 generation of bay–Peruvian hybrid scallops (Aip derived from Ai ♀ × Ap ♂) and Peruvian–bay hybrid scallops (Api derived from Ap ♀ × Ai ♂) were successfully backcrossed with Peruvian scallops (Argopecten purpuratus, Ap) and bay scallops (Argopecten irradians, Ai) to produce F2 backcrossed population (Aipi derived from Aip ♀ × Ai ♂; Aipp derived from Aip ♀ × Ap ♂; Apii derived from Api ♀ × Ai ♂ and Apip derived from Api ♀ × Ap ♂). These F2 populations were comprehensively analyzed in terms of heterozygosity, gonadal development and differentiation, fertility, genetic diversity, and offspring identification. The results revealed that the fertilization and hatching rates of the F2 generation were significantly lower than those of the parental generations. However, they exhibited normal development through larval, juvenile, and adult stages, albeit with prolonged larval development periods. Notably, the juvenile and adult stages demonstrated significant hybrid vigor. The F2 generation retained hermaphroditic characteristics but also included individuals with exclusively female gonads. Cloning of Dmrt1 and Foxl2 genes in these scallops showed high similarity with the bay scallop’s corresponding genes, and Dmrt1 is specifically expressed in the testis, while Foxl2 is specifically expressed in the ovary, as is the case in the bay scallop. Eleven pairs of polymorphic loci were selected from developed microsatellite markers for bay scallops, and the analysis revealed that the polymorphism levels in the F2 backcrossed population were higher than those in purebred parental self-crosses. Additionally, the reliability of parental genetic information in the backcrossed population has also been corroborated according to the scallop descent identification experiments. The findings of this study enhance the understanding of Aipi, Aipp, Apii, and Apip, providing a theoretical foundation for the selection and breeding of scallop species with superior traits and addressing inbreeding decline in scallop culture.