Cold Tolerance of Insects and Other Arthropods [and Discussion]

Arthropods, as poikilotherms, adapt to cold environments in a variety of ways that include extension of locomotory activity to low temperatures, enhancement of metabolic rate and maintenance of a positive energy balance whenever possible. The ecological implications for many such animals are extension of the life cycle and a requirement for an individual to overwinter several times. Prolonged sub-zero temperatures increase the risk of tissue freezing, and two main strategies have been evolved, first avoidance of freezing by supercooling, and secondly, tolerance of extracellular ice. In the first strategy, freezing is invariably lethal and extensive supercooling (to — 30 °C and below) occurs through elimination or masking of potential ice nucleators in the body and accumulation of cryoprotective substances such as polyhydric alcohols and sugars. Such species are termed freezing intolerant. The second strategy, freezing tolerance, is uncommon in arthropods and other invertebrates, and usually occurs in a single life stage of a species. Freezing of liquid in the extracellular compartment is promoted by proteinaceous ice nucleators. Freezing is therefore protective, and the lethal temperature is well below the supercooling point in freezing tolerant individuals, whereas in most freezing intolerant species it is close to or at the supercooling point. Proteins also act as antifreezes in insects of both strategies, producing a thermal hysteresis by lowering the freezing point of haemolymph in a non-colligative fashion while not affecting the melting point temperature. Recent studies and developments in arthropod cold tolerance are discussed against this background, and a broader approach than hitherto is advocated, which integrates ecological information with physiological data

Biochemical modification of plasma ice nucleating activity in a freeze-tolerant frog

Recently, we reported the presence of ice nucleating activity, apparently proteinaceous, in the plasma of a freeze-tolerant frog, Rana sylvatica, collected in autumn and spring. Although this protein has not been purified, its ice nucleating behavior can act as an internal reference for tests that attempt to modify its ability to nucleate ice formation. If the addition of a chemical reagent alters the temperature of ice crystallization compared with the control, it can be assumed that protein modification may have occurred. The ice nucleating protein in R. sylvatica showed resistance to proteolysis with four different proteases although there was a significant reduction in the temperatures of nucleation with these treatments (ANOVA P < 0.001). However, ice nucleating activity was lost when plasma was treated with the addition of urea or N-bromosuccinimide. Modification of protein sulphydryl groups with iodoacetamide did not affect the crystallization temperature (Tc) but treatment with iodoacetic acid resulted in a significant increase in Tc of plasma. An abrupt loss of ice nucleating ability was observed in plasma samples after heating above 87 °C. Anomalous potentiation of ice nucleating activity occurred when the plasma was heated to and held at temperatures between 67-75 °C

Ice nucleating activity in the blood of the freeze-tolerant frog, Rana sylvatica

Although the presence of antifreeze and ice nucleating agents in the hemolymph of insects has been well documented, there have been no reports of either of these types of agent in vertebrates. The technique of differential scanning calorimetry was used to examine the blood, serum, and plasma of a freeze-tolerant frog, Rana sylvatica, for the presence of antifreeze protein activity. Results demonstrate the absence of antifreeze protein but the presence of an ice nucleating agent that may serve as a functional component of the overwintering strategy of this species. Ice nucleating activity was detected in samples of cell-free blood, serum, and plasma, suggesting that the agent is a soluble component and possibly plasma protein. To our knowledge, the identification of ice nucleating activity in this freeze-tolerant vertebrate is novel

Intermediary metabolism during low temperature acclimation in the overwintering gall fly larva, Eurosta solidaginis

1. The levels of glycogen, lipid, protein, polyols (glycerol and sorbitol), sugars, amino acids, adenylates, and other intermediary metabolites were measured in the overwintering, third instar larvae of the gall fly, Eurosta solidaginis, sampled at specified temperatures during a controlled (1°C per day decrease) low temperature acclimation of the larvae from 15° to - 30°C. 2. Glycogen reserves were depleted as temperature was decreased, the decrease in glycogen fully accounting for the observed increases in glycerol, sorbitol, glucose, and trehalose in the larvae at low temperatures. Protein and total glyceride reserves of the larvae, however, were not altered during low temperature acclimation. 3. Temperature specific patterns of glycerol and sorbitol accumulation were found. Glycerol concentrations, which were 65% of maximum at 15°C, reached a plateau in concentration of 235 μmol/g wet wt. between 5 a