Differences in Molecular Responses to a Thermally Variable Preconditioning Treatment for Two Caribbean Coral Species Ecology and Evolution

Coral reefs around the world are increasingly threatened by rising ocean temperatures, leading to more frequent mass bleaching events. However, some corals, typically found in more thermally variable environments, have demonstrated resilience to thermal stress. Consequently, applying temperature variability for assisted acclimatization has been identified as a promising intervention for restoration efforts. While previous studies support this technique for thermal preconditioning, the underlying molecular mechanisms remain unclear. To address this research gap, we applied a variable temperature regime to promote preconditioning on two Caribbean coral species, the staghorn coral (Acropora cervicornis) and the knobby brain coral (Pseudodiploria clivosa) and evaluated changes in host and algal symbiont (Family Symbiodiniaceae) gene expression. Overall, the response to acclimatory treatments and the molecular mechanisms underlying them were species-specific. A. cervicornis had a greater transcriptional response to the temperature treatment compared to P. clivosa (583 vs. 55 differentially expressed genes). In A. cervicornis, there was significant downregulation of key stress response genes, including peroxidases, nitric-oxide synthase, and tumor necrosis factors, and an upregulation of genes involved in histone modifications. Importantly, these genes have been previously implicated in the generalized stress response of corals, suggesting that the molecular mechanisms of thermal preconditioning employ similar pathways. Considering the varying responses observed between species in this study, further research across a wider diversity of reef-building coral species is necessary before implementation at the scale needed for restoration efforts.