Repeated evolution of underwater rebreathing in diving Anolis lizards

Area of Science:

• Comparative Physiology
• Evolutionary Biology
• Herpetology

Background:

• Terrestrial animals face challenges using aquatic environments due to air-based respiration.
• Diving arthropods and some vertebrates have evolved air-based underwater respiration strategies.
• Semi-aquatic Anolis lizards inhabit neotropical streams and frequently dive for resources or refuge.

Purpose of the Study:

• To document and investigate routine air-based underwater respiration in semi-aquatic Anolis lizard species.
• To understand the physiological mechanisms and evolutionary significance of underwater rebreathing in anoles.

Main Methods:

• Conducted experiments on semi-aquatic Anolis lizards to observe and quantify underwater respiration.
• Measured partial pressure of oxygen in narial air bubbles during experimental submersion.
• Utilized phylogenetic analyses to assess the adaptiveness of rebreathing behaviors.
• Examined skin properties (hydrophobicity) and morphology (rugosity) related to air retention.

Main Results:

• Semi-aquatic Anolis lizards engage in routine underwater rebreathing of narial air bubbles.
• Oxygen levels in rebreathed air bubbles decreased during submersion, indicating respiratory gas exchange.
• Specialized rebreathing is facilitated by a hydrophobic skin layer forming an air-retaining plastron.
• Phylogenetic analyses indicate specialized rebreathing is an adaptation for semi-aquatic habitat specialists.

Conclusions:

• Semi-aquatic Anolis lizards possess a specialized air-based underwater rebreathing system.
• This 'plastron' mechanism, supported by hydrophobic skin, allows for extended dives.
• Underwater rebreathing may enhance dive performance through gas exchange, CO2 clearance, or a 'physical gill' effect.