Hypoxia Tolerance in Reptiles, Amphibians, and Fishes: Life with Variable Oxygen Availability

The ability of fishes, amphibians, and reptiles to survive extremes of oxygen availability derives from a core triad of adaptations: profound metabolic suppression, tolerance of ionic and pH disturbances, and mechanisms for avoiding free-radical injury during reoxygenation. For long-term anoxic survival, enhanced storage of glycogen in critical tissues is also necessary. The diversity of body morphologies and habitats and the utilization of dormancy have resulted in a broad array of adaptations to hypoxia in lower vertebrates. For example, the most anoxia-tolerant vertebrates, painted turtles and crucian carp, meet the challenge of variable oxygen in fundamentally different ways: Turtles undergo near-suspended…