Heat adhesion duration: A new high-throughput abalone thermal tolerance assessment method

Abstract

Under the background of continual global warming, mass summer mortalities of aquatic organisms have become more frequent, causing serious ecological and economic losses. Abalone aquaculture has experienced such losses, and thus, thermal-tolerant species are needed for mechanistic research and selective breeding programs. Hence, suitable methods to evaluate the thermal tolerance of abalone have become vitally important. In this study, a high-throughput evaluation method (heat adhesion duration, HAD) was developed based on the adhesion capacity of abalone. The stability and accuracy of the new method were verified by comparisons of survival time, Arrhenius breakpoint temperatures (ABT) of cardiac performance, and Kaplan-Meier survival curves. Positive correlations were found between HAD and survival time and between HAD and ABT, indicating that individuals with higher HAD were more thermal tolerant. The HAD values increased with acclimation temperature (20 °C, 24 °C) but were not affected by abalone size, age, or sex. The assessments of HAD, ABT, and Kaplan-Meier survival curves indicated stronger thermal tolerance of the southern population (JJ) of Haliotis discus hannai compared to the northern population (DL), suggesting plasticity of abalone in thermal tolerance. In addition, the thermal resistance of five abalone species from two hybridization systems, H. discus hannai (DD), H. gigantea (GG), H. fulgens (FF), hybrid H. gigantea ♀ × H. discus hannai ♂ (GD), and hybrid H. discus hannai ♀ × H. fulgens ♂ (DF), was evaluated by HAD and ABT, confirming the existence of heterosis for thermal tolerance. The high-throughput method developed in this study could provide a reliable indicator for molecular mechanism analyses and genetic selection for thermal tolerance in abalone.