Selection of Heat-Resistant Strains in Bohai Red Scallops and Their Transcriptomic Responses to Heat Stress

Abstract

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, we first determined the upper median lethal temperature (LT50) of Bohai Red scallops. Then we selected heat-resistant scallops (elite group, EG) by exposing Bohai Red scallops to the determined LT50 (28.9°C). Heat-resistant F1 offspring (EGF1) were reproduced from the selected individuals in EG. Tolerance to heat stress was significantly increased in EGF1, as evidenced by the elevated LT50 and the activities of some antioxidant enzymes in EGF1. Transcriptomic analyses and Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses revealed that in both the EG and (control group) CG scallops, animals were capable of resisting heat stress and maintaining cellular homeostasis probably through the action of molecular chaperones, including heat shock proteins and chaperonin-containing T-complex (CCT). There was a notable increase in the activity of pathways associated with energy metabolism and antioxidant processes, including glutathione and propionate metabolism. However, more differentially expressed genes (DEGs) were identified in the unselected control group (CG) than in EG. Furthermore, the scallops in the elite group showed a strong immune profile, with immune-related DEGs enriched in the PI3K-Akt and Toll-like receptor pathways, which may induce inflammatory factors to defend against heat stress. Our results in this study may contribute to understanding the mechanisms underlying heat stress adaptation in the Bohai Red scallops and provide a theoretical basis for the inheritance and evolution of heat-resistant traits.

Keywords: The scallop 'Bohai Red', heat-resistant breed selection, transcriptomics, antioxidant, immune system