Freeze Tolerance and Freeze Avoidance in Ectotherms

Abstract

The vast majority of ectothermic animals on earth must elude exposure to subzero temperatures to prevent the lethal freezing of body fluids. For this reason the northern ranges of many ectotherms are limited; thus, few terrestrially-hibernating reptile and amphibian species are found in northern latitudes (Behler and King 1979) and the diversity of invertebrate fauna in the intertidal zones of polar regions is low (Aarset 1982). Migration or the choice of warm hibernacula allow some species to elude subzero temperatures during winter (e.g., monarch butterflies fly to Mexico, toads dig down 1 m or more into the earth to avoid the frost line, garter snakes gather by the hundreds in undergound dens, turtles, many frogs, and various insects overwinter under water). For many other species, however, the challenges of life below 0°C are met with physiological and biochemical adaptations for cold hardiness.