Acute Heat Priming Dampens Gene Expression Response to Thermal Stress in a Widespread Acropora Coral

Physiological plasticity is fundamental for resisting environmental change. As climate change accelerates and environmental stressors become more frequent, understanding how habitat-forming species shift their physiology to match their environment is essential for predicting broader ecosystem responses. In this study, we examined whether prior exposure to sub-bleaching heat stress influenced the gene expression responses to a subsequent thermal challenge in a common reef-building coral. We primed Acropora corals from the World Heritage-listed Ningaloo Reef (WHNR) to acute (24 h) sub-bleaching temperatures (+5°C from the mean monthly maximum MMM, 32°C) before subjecting them to a more intense thermal challenge (+6°C from MMM, 33°C), and assessed the physiological and transcriptional responses in both naïve (no prior preconditioning) and primed corals compared to controls. Both groups mounted large gene expression responses to heat stress (33°C), which returned to baseline after a recovery period (16 h) at control temperatures (27°C, MMM), with no visible signs of physiological stress. However, primed corals showed a dampened stress response relative to naïve corals, marked by a 28% decline in differentially expressed genes and an overall reduction in intensity of expression of those genes compared to controls. Similar patterns were observed in the symbiotic partners, which showed a dampened response within the primed corals compared to the controls, despite no detectable declines in photosynthetic performance within either treatment. Our results show that short-term preconditioning of corals is associated with transcriptional dampening of key stress response genes, and that corals are capable of rapid transcriptional recovery and resilience to recurrent heat stress.