Variations of Supercooling Capacity in Intertidal Gastropods

SIMPLE SUMMARY: Intertidal snails can survive freezing (i.e., tolerate the formation of ice in their body) at very low subzero temperatures. The temperature at which body fluids spontaneously freeze (supercooling point, SCP) varies among intertidal snails, potentially depending on their geographic and vertical distributions. The objective of this study was to understand the variations of SCP in common intertidal snails in China. We compared nine intertidal species with different geographic and vertical distributions. Results indicated that at the intraspecies level, the higher the cooling rate of an individual was, the higher the SCP was. High-shore species living in Northern China showed lower SCPs, while southern high-shore species had higher SCPs. These results suggested that cooling rate and local winter temperatures contribute to the difference in SCPs within and between species and might be useful for evaluating and predicting species distribution. ABSTRACT: Winter low-temperature confines species distribution. Intertidal gastropods are distributed from tropical to polar zones, facing variable intensities and durations of low temperatures. They usually set their supercooling points (SCPs) at high subzero temperatures to stimulate freezing. However, the variations in SCP in intertidal gastropods at intraspecific and interspecific levels remain poorly understood. Here, we measured the body size, cooling rate, and SCP of nine intertidal gastropod species in China. These species were distributed in high or middle intertidal zone with different geographic distributions. The average SCPs (−4.27~−7.10 °C) and the coefficients of variation of SCP (22.6%~45.9%) were high in all species. At the intraspecific level, the supercooling capacity was positively correlated with the cooling rate. Interspecifically, the supercooling capacity was closely related to the cooling rate, and also to the species’ geographical distribution. Northern high-shore species showed lower SCPs, while southern high-shore species had higher SCPs. There was no difference in SCP between widespread high- and mid-shore species. Our results indicated that the supercooling capability is potentially an adaptative response to the local winter temperatures, and the cooling rate is a factor in determining the difference in SCP at the intraspecific and interspecific levels.