Ice Nucleation in Freeze - Tolerant Vertebrates

The survival of freeze-tolerant vertebrates requires that ice nucleation in tissues be initiated at relatively high temperatures. Three current hypotheses for the initiation of freezing in these animals are: a) inoculation by contact with ice crystals in the external environment; b) nucleation by ice-nucleating bacteria associated with the animal; and c) nucleation by icenucleating proteins in the blood. The available evidence indicates that ice inoculation is the most important mechanism under natural conditions, although ice-nucleating bacteria harbored in the gut or skin during winter may function as an auxiliary system to promote crystallization, albeit at slightly lower temperatures. Despite the intriguing similarities between the blood icenucleating agents of some vertebrates and those of certain freeze-tolerant invertebrates, these agents seem unlikely to play an analogous, adaptive role in freeze tolerance.