The question of whether a lizard can breathe underwater is generally answered with a simple “no,” as these reptiles are air-breathing vertebrates. However, a closer look at the adaptations evolved by certain species reveals a more complex and fascinating reality. Most lizards must rely entirely on the air above the surface, using physiological mechanisms to extend their time submerged. A select few have developed truly extraordinary behaviors that mimic a form of underwater respiration, allowing them to remain submerged for periods far exceeding what simple breath-holding would permit.
The Fundamental Limitation of Lizard Respiration
Lizards, like all reptiles, rely exclusively on pulmonary respiration, meaning they breathe using lungs designed to extract oxygen from atmospheric air. Their respiratory system lacks the specialized structures necessary to process dissolved oxygen from water, such as the gills found in fish. The lungs of a lizard contain internal subdivisions, or faveoli, which increase the surface area for gas exchange, but this system is strictly adapted for air. The mechanical process of breathing involves the movement of the ribs and associated muscles to expand and contract the body cavity. Since lizards do not possess a muscular diaphragm like mammals, a submerged lizard cannot perform the physical movements needed to utilize the oxygen within that water.
Extended Apnea: The Art of Holding Breath
Despite their reliance on atmospheric air, many semi-aquatic and marine lizards are highly skilled at extended breath-holding, known as apnea. This ability is a sophisticated physiological strategy to conserve the oxygen stored in the blood and lungs. The Marine Iguana (Amblyrhynchus cristatus), the world’s only sea-going lizard, exemplifies this adaptation, regularly diving to graze on underwater algae.
When the Marine Iguana submerges, it triggers a powerful set of reflexes known as the diving response. A key component is bradycardia, where the heart rate dramatically slows, dropping from around 40 beats per minute to as low as 10 beats per minute during a dive. This reduced heart rate significantly lowers the rate at which the body consumes oxygen. The response is paired with peripheral vasoconstriction, which constricts blood vessels supplying the extremities and non-vital organs. By prioritizing blood flow to the brain and heart, these adjustments allow large lizards to remain submerged for up to thirty minutes while actively foraging.
The Unique Case of Aquatic Rebreathing
A truly unique adaptation has been discovered in certain species of Neotropical anole lizards, such as the water anole (Anolis aquaticus), which exhibit a behavior termed “aquatic rebreathing.” When these small lizards dive to escape predators, they exhale a bubble of air that adheres to their snout and head. The lizard then cycles the air from this bubble back into its lungs through its nostrils. This bubble acts like a temporary, reusable air tank, allowing the lizard to remain submerged for surprisingly long durations, sometimes up to 18 minutes.
Researchers have confirmed the functional role of this bubble by measuring the oxygen content within it, which steadily decreases over the course of a dive. This decrease confirms that the lizard is indeed using the air supply to supplement the oxygen already stored in its lungs. The bubble’s function may go beyond simply recycling exhaled air, potentially acting as a “physical gill.”
Because the bubble’s surface is in direct contact with the water, gases can diffuse across the air-water interface. As the lizard uses oxygen, the partial pressure of oxygen inside the bubble drops, which may draw dissolved oxygen from the surrounding water into the bubble. Simultaneously, the carbon dioxide exhaled by the lizard, which is highly soluble in water, can potentially diffuse out of the bubble and into the stream. This remarkable behavior, facilitated by the lizard’s water-repellent skin, grants these small reptiles a significant survival advantage.