Time-course transcriptome analysis identifies increased receptor-mediated signaling prior to synchronous spawning in Acropora digitifera

Sympatric coral colonies often release gametes synchronously on one to several nights each year, a phenomenon known as coral mass spawning. For corals, the timing of gamete release is crucial for successful fertilization and is thought to be regulated by a complex interaction between genetic mechanisms and environmental factors such as lunar cycles, temperature, and photoperiod. Although previous studies have examined transcriptomic differences under contrasting environmental conditions (e.g., full versus new moon), time-course transcriptome analyses provide deeper insight into the dynamic molecular processes that precede spawning. Here, we present transcriptome profiles of Acropora digitifera collected during the spawning season to investigate gene expression changes associated with the initiation of spawning. Our analyses suggest the involvement of serotonergic receptor and steroid-mediated signaling in triggering gamete release. We also detected upregulation of an alpha1-adrenergic receptor gene prior to spawning, which may play a role in regulating smooth muscle contraction required for the coordinated release of gamete bundles. In contrast, transcriptomic analyses of the symbiotic algae did not reveal consistent expression patterns associated with host spawning timing, suggesting that algal symbionts are unlikely to directly control this process. Together, these findings provide new insights into the molecular mechanisms underlying coral mass spawning and highlight candidate signaling pathways that may regulate this remarkable reproductive synchronization.