Mechanisms and evolution of resistance to environmental extremes in animals.

When animals are exposed to an extreme environmental stress, one of three possible outcomes takes place: the animal dies, the animal avoids the environmental stress and survives, or the animal tolerates the environmental stress and survives. This review is concerned with the third possibility, and will look at mechanisms that rare animals use to survive extreme environmental stresses including freezing, desiccation, intense heat, irradiation, and low-oxygen conditions (hypoxia). In addition, an increasing understanding of the molecular mechanisms involved in environmental stress tolerance allows us to speculate on how these tolerances arose. Uncovering the mechanisms of extreme environmental stress tolerance and how they evolve has broad implications for our understanding of the evolution of early life on this planet, colonization of new environments, and the search for novel forms of life both on Earth and elsewhere, as well as a number of agricultural and health-related applications.