Biological ice nucleation and ice distribution in cold-hardy ectothermic animals

Reviews where ice starts in a cooling animal, the proteins and particles that make it start, and how the resulting ice is distributed between and within tissues.

Studied in

Insecta, Amphibia, Reptilia

Sample size

review

Freeze-tolerant animals often produce ice-nucleating proteins that trigger freezing at high sub-zero temperatures in extracellular spaces, while freeze-avoiding animals do the opposite — clearing their guts and removing nucleators to stay liquid as far below zero as possible.

• Ice distribution within tissues is technically hard to observe and much of the evidence is indirect.
• Nucleator identity is established in relatively few species.

• Freeze tolerance

  An animal facing sub-zero temperatures either stops ice forming or permits it. These are opposite solutions: one group removes everything ice could start from, the other makes proteins whose job is to start it.

• Freeze tolerance

  Freeze-tolerant animals make themselves freeze on purpose, at the highest sub-zero temperature they can manage. A slow freeze starting at −1 °C is survivable; a sudden one at −8 °C is not.