Physiological mechanisms of shell microstructural regulation in Japanese pearl oyster under hypoxic stress: Insights into molluscan resilience against environmental changes

Investigating the anomalous expression of nacre, one of the most common microstructures of the Mollusca, as an environmental archive and its genomic background provides novel insights into sclerochronology and biomineralization. In this study, we aimed to elucidate the physiological responses of the Japanese pearl oyster, Pinctada fucata, under hypoxia, focusing on shell microstructure plasticity. We conducted RNA-seq analysis in specimens from different depths with different oxygen concentrations and observed changes in microstructures. We found differences in shell microstructure and distinct gene expression profiles between hypoxia and normoxia. Several shell matrix protein genes were downregulated under hypoxia, suggesting their role in shell formation. We estimated the dissolved oxygen threshold affecting the physiological resistance of P. fucata to microstructural alterations. These results indicate that molluscan shell microstructures are under genetic controls in response to environmental stressors. Our findings on anomalous nacre may serve as a novel sclerochronological proxy for understanding hypoxic occurrences.