Metabolic Shifts and Muscle Remodeling as Pro-Survival and Energy Compensation Strategies in Photosymbiotic Giant Clams after Bleaching

. The density and structure of unique muscle fibers with high collagen content, observed in siphonal mantle of these animals, were negatively altered after heat stress. These changes were associated with a metabolic shift from carbohydrates and fatty acids to amino acids as the breakdown of collagen-rich muscle fibers can partially compensate for energy loss during bleaching. Such a shift was proposed to be regulated by AMP-activated protein kinase (AMPK) signaling and FoxO-atrogin pathways. Overall, our study highlights a pro-survival mechanism in giant clams through plastic regulation, which likely contributes to their relatively high environmental resilience during bleaching.