The phylogeny of central chemoreception.

Area of Science:

• Physiology
• Evolutionary Biology
• Comparative Respiratory Physiology

Background:

• Respiratory chemoreceptors detect changes in carbon dioxide (CO2) and hydrogen ions (H+).
• These receptors are crucial for regulating breathing across vertebrate species.
• Their evolutionary origins and localization (peripheral vs. central) vary significantly.

Purpose of the Study:

• To investigate the evolutionary history and localization of CO2/H+ chemoreceptors in vertebrates.
• To understand the transition from peripheral to central chemoreception with the advent of air-breathing.
• To explore the potential for multiple independent origins of central chemoreception.

Main Methods:

• Comparative analysis of chemoreceptor function across diverse vertebrate groups (fish, amphibians, reptiles, birds, mammals).
• Examination of developmental changes in branchial artery derivatives and associated chemoreceptors.
• Review of physiological and anatomical evidence for peripheral and central CO2/H+ sensing.

Main Results:

• Peripheral CO2/H+ chemoreceptors, primarily in fish gills, sense external aquatic conditions.
• In air-breathing tetrapods, chemoreceptors associated with branchial artery derivatives sense arterial PCO2/pH.
• Evidence suggests central CO2/H+ chemoreception arose with air-breathing and may have multiple origins within species.

Conclusions:

• Chemoreceptor sensitivity shifted from environmental to arterial PCO2/pH with the evolution of air-breathing.
• Central chemoreception likely evolved independently multiple times, coinciding with the independent evolution of air-breathing.
• Multiple central sensing sites for CO2/H+ exist within species, indicating complex evolutionary pathways.