Genomic and transcriptomic analyses reveal the molecular mechanism of heterosis in hybrid largemouth bass (Micropterus salmoides)

Populations of largemouth bass (Micropterus salmoides) are showing diminishing genetic diversity and degradation of valuable traits, so it is important to enhance their genetic diversity. Two geographically isolated populations of largemouth bass — the protospecies from the United States and the farmed population in Jiangsu, China — were used to produce hybrids. Two hybrid populations (NC and CN) were produced, and the growth performance, genetic diversity, and transcriptomes were compared between the hybrids and purebred groups (CC and NN). The weight gain rate and specific growth rate were significantly higher in the hybrid groups than in the purebred groups, and the hybrids showed significant growth heterosis. The values of diversity indices (observed and expected heterozygosity, polymorphism information content, and nucleotide diversity) were higher in the hybrid groups than in the purebred groups. Differentially expressed genes (DEGs) in the hybrids predominantly exhibited dominant expression patterns; 544 and 180 DEGs in NC and CN, respectively, showed overdominant expression. In NC, genes with overdominant expression were enriched in pathways associated with the synthesis and metabolism of various materials, including amino acids, lipids, and carbohydrates. Many DEGs between the hybrid and purebred groups were significantly enriched in the protein processing in endoplasmic reticulum pathway, which is associated with non-specific immune regulation. Genes in regions under strong selection pressure played important roles in material metabolism and synthesis. Thus, hybridization enhances the genetic diversity of largemouth bass and improves its growth performance. Our findings provide new information about the mechanisms of heterosis, offering insights for future breeding research.