Hibernating without oxygen: physiological adaptations of the painted turtle

Area of Science:

• Physiology
• Biochemistry
• Ecology

Background:

• Temperate freshwater turtles face prolonged periods of anoxia (lack of oxygen) during winter, often trapped under ice or in oxygen-depleted environments.
• Survival requires maintaining function during anoxia for extended durations, posing significant physiological challenges.

Purpose of the Study:

• To elucidate the physiological mechanisms enabling freshwater turtles to survive prolonged anoxic conditions during winter.
• To understand the interplay between metabolic depression and shell-based buffering systems.

Main Methods:

• The study focuses on the physiological and biochemical adaptations of freshwater turtles to anoxia.
• Analysis of metabolic rate depression, including the glycolytic pathway and ATP-consuming processes.
• Investigation of shell and skeletal buffering mechanisms for lactic acid neutralization.

Main Results:

• Turtles exhibit a coordinated depression of metabolic processes, significantly slowing ATP production and consumption.
• Substrate depletion and lactic acid production rates are greatly reduced.
• The turtle's shell and skeleton provide extensive buffering capacity, sequestering accumulated lactic acid through carbonate release and uptake.

Conclusions:

• Freshwater turtles employ a dual strategy of metabolic suppression and shell/skeletal buffering to survive anoxia.
• These adaptations permit survival for 3-4 months at low temperatures (3°C) with extremely high circulating lactate levels (≥150 mmol l⁻¹).
• This resilience is key to the survival of temperate freshwater turtle populations through harsh winter conditions.