The mechanism of the cryoprotective effect of glycerol in beetles tolerant to freezing

The mechanism of the cryoprotective effect of glycerol has been studied experimentally on freezetolerant Pytho depressus beetles. The lowest tolerated temperature of the beetles was determined as a function of their pre-freezing glycerol concentration. The temperatures, at which the potentially harmful non-penetrating solutes would reach the injurious level in the frozen body fluid were estimated for solutions with different pre-freezing concentrations of glycerol, assuming a colligative effect of glycerol. The lowest tolerated temperature of the beetles ranged from ?7.5 C for beetles lacking glycerol to ?27 C for beetles having a pre-freezing glycerol concentration of 1500 mmolal in their body fluid. The estimated temperatures fitted these observations almost perfectly. Thus, the results support the view that the cryoprotective effect of glycerol in freeze-tolerant beetles is based on the colligative properties of the substance.