Oxygen transport is not compromised at high temperature in pythons

Area of Science:

• Physiology
• Ecology
• Herpetology

Background:

• The oxygen and capacity limited thermal tolerance (OCLTT) model predicts reduced oxygen transport at high temperatures.
• Ectothermic vertebrates may face thermal tolerance limits due to oxygen transport capacity.

Purpose of the Study:

• To test the applicability of the OCLTT model in an air-breathing ectotherm, the snake Python regius.
• To investigate the relationship between temperature, oxygen uptake, cardiac performance, and blood gases in snakes.

Main Methods:

• Measurements of oxygen uptake (V̇(O₂)), cardiac performance, and arterial blood gases.
• Progressive temperature increase from 30 to 40°C in fasting and digesting snakes.
• Analysis of acid-base balance and arterial partial pressure of oxygen (PO₂).

Main Results:

• Oxygen uptake increased exponentially with temperature in fasting snakes.
• Digesting snakes showed plateaued oxygen uptake at high temperatures (3-4x fasting levels).
• Snakes maintained normal acid-base balance, high aerobic metabolism, and adequate arterial PO₂ across temperatures.

Conclusions:

• No evidence of reduced oxygen transport capacity at high temperatures in Python regius.
• The OCLTT model's predictions may not apply to this species.
• Upper thermal tolerance in Python regius is likely limited by factors other than oxygen transport.