Non-invasive assessment of cold tolerance in the ivory shell (Babylonia areolata) using PPG-based cardiac performance indicators

Cold stress constrains the stable production and regional expansion of the ivory shell, Babylonia areolata , yet rapid and non-destructive tools for evaluating individual cold tolerance remain limited. We established a photoplethysmography (PPG)-based method to continuously monitor cardiac responses during acute cooling and rewarming and derived three indicators: critical arrhythmia temperature (CAT), cardiac decline rate (CDR), and cardiac recovery temperature (CRT). No significant sex- or size-related differences in these three indicators were detected within the tested adult range. CAT, CDR, and CRT were negatively associated with post-challenge survival duration and differed between survivors and non-survivors, supporting their biological validity as individual-level cold-tolerance indicators. The method was subsequently applied to three parental-origin groups from Fujian, Hainan, and Thailand. Cardiac responses to decreasing temperature differed among groups, and the Fujian-origin group showed lower cardiac thermal sensitivity in the critical low-temperature interval together with lower CAT, CDR, and CRT. These findings indicate greater cardiac stability and cold-tolerance potential of Fujian-origin individuals under the standardized acute challenge. PPG-based cardiac phenotyping therefore provides a rapid, quantitative, and non-destructive tool for screening live individuals, evaluating parental resources, and supporting overwintering management and cold-tolerant breeding in B. areolata .