Evolution of vertebrate respiratory central rhythm generators

Area of Science:

• Neuroscience
• Evolutionary Biology
• Comparative Physiology

Background:

• Central rhythm generators for ventilation are well-studied in limited vertebrate groups (lamprey, anurans, turtles, mammals).
• Information is scarce regarding the evolutionary transition from aquatic respiration in fish to terrestrial air-breathing in amniotes.

Purpose of the Study:

• To review the known respiratory rhythm-generating circuits across vertebrate classes.
• To trace the evolutionary trajectory of these circuits, focusing on key transitional periods.
• To identify knowledge gaps crucial for understanding vertebrate respiratory evolution.

Main Methods:

• Comparative analysis of existing literature on respiratory neurobiology in diverse vertebrate taxa.
• Examination of developmental origins of respiratory networks from rhombomeres.
• Hypothesizing the evolutionary fate of oscillator circuits during vertebrate evolution.

Main Results:

• Fish respiratory rhythm generators appear as single oscillators controlling both breathing phases.
• Amniotes exhibit independent oscillators for inspiration and expiration, projecting to distinct motoneuron pools.
• Amphibians, particularly anurans, present a complex transitional case with unresolved questions.

Conclusions:

• The evolution of vertebrate respiratory rhythm generators involved a divergence from single, phase-spanning oscillators to independent inspiratory and expiratory oscillators.
• Understanding the anuran system is critical for elucidating the fish-to-amniote transition.
• Further research is needed to fully map the evolutionary history of these vital neural circuits.