Glucose Prevents Formation of Ice Crystals

Biological Strategy

Spring peeper

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Protect From Ice

Freezing temperatures can be difficult for living systems to manage. They can cause ice crystals to form in blood and tissues, which causes damage to cells and ultimately, death. Living systems can’t afford the energy required to melt ice crystals, so instead, many have strategies to prevent crystals from forming in the first place. Many amphibians, plants, and insects have chemicals that act as antifreeze to prevent icy crystal formation. Another challenge ice presents is that it creates a slick surface, requiring friction to traverse. This is why polar bears’ paws have a rough surface that grips ice.

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Protect From Temperature

Many living systems function best within specific temperature ranges. Temperatures higher or lower than that range can negatively impact a living system’s physiological or chemical processes, and damage its exterior or interior. Living systems must manage high or low temperatures using minimal energy, which often requires controlling responses along incremental temperature changes. To do so, living systems use a variety of strategies, such as avoiding high or low temperatures, removing excess heat, and holding heat in. Insulation is a well‑known example of managing low temperatures by retaining heat using thick layers of hair, fur, or feathers to hold warm air next to the skin.

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Amphibians

Class Amphibia (“to live a double life”): Frogs, salamanders, toads

Amphibians live a “double life” by being able to survive both on land and in water. Unlike reptiles with dry, scaly skin, amphibians have smooth skin that needs to be kept moist. Many live in the water through development and start life with gills, and then transition to breathing with lungs. They can get even more oxygen through cutaneous respiration, or breathing through their skin. This class represents the first animal group to be able to efficiently walk on land—aided by the well-defined limbs that gave them a “leg up” on their finned competitors.

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Glucose produced by spring peepers in cold weather reduces ice crystal formation by concentrating the frogs' body fluids.

“In 1997, biologists from Pennsylvania’s Slippery Rock University revealed that the spring peeper (Pseudacris crucifer), a tiny species of North American frog, produces glucose during frosty weather to concentrate its body fluids and so reduce ice crystal formation, enabling it to survive for up to three days with almost half of its total body fluid frozen. It returns to a fully active state in only a day after thawing out.” (Shuker 2001:110)

“To prevent lethal freeze injury, these [North American] frogs initiate intensive hepatic glycogenolysis immediately after the onset of tissue freezing and concomitantly distribute the glucose throughout their bodies, raising levels of tissue glucose by as much as 10- 100 X above normal (Storey and Storey, 1984). The treefrog Hyla versicolor is exceptional because it converts most of the glucose into glycerol, which is then distributed to body tissues (Storey and Storey, 1985). Because so much of their body water is sequestered into ice (to 70%), frozen frogs cannot sustain systemic functions, including breathing, heartbeat, and blood flow (Layne et al., 1989). Upon thawing, freeze-tolerant frogs resume cardiovascular functions first, whereas, other functions resume during the ensuing hours (Layne and First, 1991)…Pseudacris crucifer mobilizes glucose to levels that are comparable to most other freeze-tolerant frogs.” (Layne and Kefauver 1997:260)

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