Respiratory control and CO2 conductance: temperature effects in a turtle and a frog

Area of Science:

• Comparative physiology
• Respiratory system function
• Amphibian and reptile biology

Background:

• The respiratory control systems in lung-breathing turtles (Pseudemys scripta) and bimodal breathing frogs (Rana catesbeiana) exhibit distinct mechanisms.
• Understanding these systems is crucial for comprehending ectotherm adaptation to environmental temperature fluctuations.

Purpose of the Study:

• To compare the respiratory control systems of a turtle and a frog.
• To analyze CO2 exchange via pulmonary ventilation and skin diffusion across different temperatures.
• To investigate the temperature dependence of respiratory conductances.

Main Methods:

• Comparative analysis of respiratory control in Pseudemys scripta and Rana catesbeiana.
• Application of convective and diffusive conductance equations to model CO2 exchange.
• Measurement of PaCO2 (partial pressure of carbon dioxide in arterial blood) and MO2 (oxygen consumption) to predict conductance values.

Main Results:

• Pulmonary ventilation is the primary respiratory control in both species, resembling mammalian systems.
• Frog skin CO2 exchange is largely passive with minimal adaptive control.
• Conductance values for both lung and skin CO2 exchange showed moderate increases with temperature, attributed to similar Q10 values for PaCO2 and MO2.

Conclusions:

• The blunted temperature dependence of respiratory conductances allows both lung and skin breathers to regulate PaCO2 and pHa effectively across their ectothermic temperature range.
• The findings highlight the adaptive respiratory strategies in ectotherms for maintaining homeostasis.
• Respiratory effector mechanisms are finely tuned to environmental temperature variations in these species.