Physiology of Freeze-Tolerance in Insects

Evolution of Freeze-Tolerance in Insects
The Dangers of Freeze-Tolerance
Protein Ice Nucleators
Future Applications of Freeze-Tolerance Mechanisms
Literature Cited



Freeze-tolerance mechanisms are employed by a wide range of animals in attempt to survive the harsh cold temperatures of winter and arctic environments. Freeze-tolerance is defined as the conversion of 50% or more of an animal’s total body water into extracellular ice. These animals have adapted to counter the negative consequences associated with freezing. Freeze-tolerance is one of two strategies for coping with temperatures below the freezing point of an animals’ bodily fluids; the other approach is freeze-avoidance. Freeze-avoidance is when animals are able to preserve the liquid state of their bodily fluids at extremely low temperatures; a phenomenon known as supercooling. Species that are freeze-tolerant often use supercooling to slow the freezing process. They also use specifc proteins and cryoprotectants to prevent damage from freezing. In order to survive freezing, these animals have evolved adaptations at the behavioral, physiological, and biochemical levels (Storey, 1996).

The flightless midge, Beligica Antarctica The wooly bear caterpillar, Pyrrhartia isabella

Photo (right) from IronChris.

            Insects are the most freeze-tolerant animals in the world. As a result, insects are able to survive where other animals cannot; for example arctic environments where the temperature routinely drops below -70 degrees Celsius (Duman, 2001). This is remarkable considering the fact that insects are ectothermic and have limited ability to regulate their body temperature. There are variations in the ways in which insects employ freeze-tolerant mechanisms; some arctic species are able to maintain freeze-tolerant abilities throughout the entire year while other species use freezing strictly as an overwintering strategy. Overall there are more freeze-tolerant species in arctic regions than temperate areas because freeze-tolerance is energetically less costly than freeze-avoidance at extreme low temperatures (Strathdee, 1998).

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