Cryoprotective dehydration

In the springtail, Onychiurus arcticus, dehydration forms a critical component of its overwintering strategy (Holmstrup and Somme 1998; Worland et al. 1998). Fully hydrated animals have a limited supercooling capacity of about —6.5°C. This suggests that the species would be unable to survive temperatures of as low as —20°C that are encountered in its microhabitat. However, when exposed to subzero temperatures its body water content declines significantly, with the final value depending on the temperature, but capable of being as low as <10 per cent of the initial value. This is in keeping with the increase in the vapour pressure difference between supercooled water and ice that is

Figure 5.21 The relationship between total body water content and melting point in individuals of Onychiurus arcticus.

Source: Reprinted from Journal of Insect Physiology, 44, Worland etal., 211-219, © 1998, with permission from Elsevier.

Total body water (g/g dry weight)

Total body water (g/g dry weight)

Figure 5.21 The relationship between total body water content and melting point in individuals of Onychiurus arcticus.

Source: Reprinted from Journal of Insect Physiology, 44, Worland etal., 211-219, © 1998, with permission from Elsevier.

characteristic of declining temperatures (Holmstrup and Somme 1998). The decline in body water content results in a substantial lowering of the melting point (Fig. 5.21), such that it equals the ambient temperature (therefore the animal is not supercooled). There is therefore no risk of tissue ice formation or inoculation from the environment. Trehalose, a known anhydroprotectant that is thought to stabilize membranes and proteins, also increases in this springtail in response to cold, and together with dehydration results in a decline in the melting point of the body fluids. This cryopro-tective dehydration (which is not the equivalent of prolonged supercooling) is clearly the most significant strategy for the survival of the low temperatures characteristic of this species' Arctic habitats (Holmstrup and Somme 1998; Worland et al. 1998).

Was this article helpful?

0 0

Post a comment