Selection of heat-resistant strains in Bohai Red Scallops and their transcriptomic responses to heat stress

Temperature has consistently been a critical environmental factor in the cultivation of scallops, and with global warming, marine animals will likely experience even more exposure to heat stress. Thus, it is necessary to select heat-resistant strains in scallops. In this study, heat stress selection was performed on the unselected Bohai Red scallop (CG) using the measured upper median lethal temperature (LT₅₀), yielding an elite group (EG), from which the heat-resistant F1 offspring (EGF1) were reproduced. Tolerance to heat stress was significantly increased in EGF1, as evidenced by the elevated LT₅₀ and the activities of certain antioxidant enzymes. Transcriptomic analyses and GO and KEGG analyses demonstrated that both EG and CG animals may mitigate heat stress and maintain cellular homeostasis through pathways associated with protein folding, energy metabolism, and antioxidant mechanisms. Furthermore, the scallops in the EG group showed a strong immune profile, with immune-related DEGs enriched mainly in interleukin-1 receptor binding and Toll-like receptor pathways. Conduct GO and KEGG enrichment analyses on the MM.darkolivegreen module, which demonstrates the strongest positive correlation with heat stress in Weighted Gene Co-expression Network Analysis (WGCNA). These analyses revealed pathways consistent with those identified in differentially expressed genes (DEGs), thereby providing mutual validation of the results. These results enhance our understanding of the molecular mechanisms driving heat stress adaptation in Bohai Red scallops and establish a theoretical foundation for the inheritance and evolution of heat-resistant traits.