Oxidative cost to ventilation in a turtle, Pseudemys floridana

Area of Science:

• Comparative Physiology
• Respiratory Physiology
• Bioenergetics

Background:

• Ventilation represents an energy cost for all animals.
• Understanding this cost is crucial for metabolic studies, especially in ectotherms with variable body temperatures.
• Previous estimates for reptiles are limited.

Purpose of the Study:

• To quantify the oxidative cost of ventilation in Pseudemys floridana.
• To determine how this cost varies with body temperature.
• To relate ventilation cost to overall metabolic rate (VO2) and ventilation rate (VE).

Main Methods:

• Artificial ventilation of Pseudemys floridana lungs with excess airflow.
• Measurement of oxygen consumption (VO2) during artificial ventilation and at rest.
• Calculation of oxidative cost of ventilation per unit of gas ventilated.
• Relating cost to body temperature (BT) and body weight (Wt).

Main Results:

• At 22°C, the oxidative cost of ventilation was 0.0047 ml O2/ml gas ventilated, approximately 10 times that of humans.
• The relative oxidative cost of ventilation (as % of resting VO2) is described by the equation: cost = 0.47 VE/VO2.
• Relative cost decreased with increasing body temperature, from 30% VO2 at 10°C to 10% VO2 at 37°C.

Conclusions:

• Ventilation imposes a substantial metabolic cost on Pseudemys floridana, particularly at lower body temperatures.
• The inverse relationship between ventilation cost and body temperature has implications for acid-base balance (arterial PCO2) and metabolic regulation.
• This study provides quantitative data on respiratory energetics in a reptile model.