Living without oxygen: lessons from the freshwater turtle

Area of Science:

• * Zoology and comparative physiology.
• * Vertebrate adaptation to extreme environments.

Background:

• * Freshwater turtles, particularly painted turtles (Chrysemys picta), are exceptionally tolerant to anoxia (lack of oxygen).
• * They can survive up to 5 months submerged in anoxic conditions at low temperatures (3°C).

Purpose of the Study:

• * To elucidate the integrative physiological adaptations enabling extreme anoxia tolerance in painted turtles.
• * To understand the roles of metabolic depression and acid-base regulation in survival.

Main Methods:

• * Analysis of metabolic rate reduction during anoxic conditions.
• * Investigation of acid-base balance mechanisms, focusing on skeletal buffering capacity.
• * Examination of lactic acid buffering and storage in bone and shell.

Main Results:

• * A significant reduction in energy metabolism to approximately 10% of the normoxic rate was observed.
• * Turtles effectively defend their acid-base status against severe lactic acidosis.
• * Skeletal and shell carbonate reserves are mobilized to buffer lactic acid, which is then stored within these structures.

Conclusions:

• * The extraordinary anoxia tolerance of painted turtles is attributed to a combination of profound metabolic rate reduction and a robust skeletal buffering system.
• * The shell and bone act as crucial reservoirs for buffering and storing acid generated during anaerobic glycolysis.