Slight thermal stress exerts genetic diversity selection at coral (Acropora digitifera) larval stages

Background Rising seawater temperatures increasingly threaten coral reefs. The ability of coral larvae to withstand heat is crucial for maintaining reefs. While the reproductive process from spawning to larval dispersal is extensively studied, the influence of heat stress on genetic diversity at the individual larval level still needs to be clarified. Results This study investigates the larval response to heat stress before acquiring symbiotic algae, aiming to elucidate the relationship between coral genetic diversity and heat stress. Larvae sourced from eight Acropora digitifera colonies were subjected to ambient temperature (28°C) and heat conditions (31°C). The impact of heat stress on larval genetic diversity was assessed through sequencing. While overall genetic diversity, represented by π, did not significantly differ between the control and heat-exposed groups, Tajima’s D differed, indicating different selective pressures in each group. Twelve larval protein-coding sequences were identified on these loci, and the codon evolution of most of these genes showed signs of adaptive evolution. These results demonstrate the complex nature of the selective pressures operating in coral larvae under different temperatures, suggesting that corals might have experienced similar selection pressures during speciation. Conclusion These findings underscore the significance of genetic diversity in coral reproduction for maintaining reef ecosystems. They also indicate that even minor heat stress can exert significant selective pressure, potentially leading to profound implications for coral reef ecosystems. This research is crucial for understanding and mitigating the impact of rising seawater temperatures on coral reefs.