A team of evolutionary biologists, including faculty at the State University of New York at Binghamton, says some Anales lizards have adapted to re-breathing the exhaled air underwater using bubbles attached to their noses. The lizard, which lives along a new tropical stream, often dives into the water and stays underwater for up to 16 minutes.
Lindsey Swierk, an assistant research professor of biological sciences at Binghamton University, documented the animal’s behavior in Costa Rica in 2019 and was shocked to see the small reptile drown itself for so long and use GoPro to record it underwater.
“It’s easy to imagine the advantage these small, slow Western doctors get by avoiding their predators underwater — they’re really hard to spot!” Swierk said. “But the real question is how they managed to stay underwater for so long.”
In the experiment, they found that the Anores lizards could breathe underwater by “re-breathing” the air they exhaled, which subtly trapped them in their skin and the surrounding water.
“We found that Anoles lizards exhale air into a bubble that adheres to their skin,” said lead author Chris Boccia, a recent master’s degree in science from the University of Toronto. “The lizard then re-inhales the air, which we call ‘re-breathing according to scuba diving technology.”
The researchers believe that the hydrophobic skin they observed in all sampled lizards may be adaptive, facilitating the repeated evolution of specialized respiration of species that dive frequently. Air-based respiration mechanisms may improve diving performance by incorporating dead cavity air from the mouth or abdominal cavity into the lungs, facilitating the removal of carbon dioxide, or allowing oxygen (the “physical gill” mechanism) to be absorbed from the surrounding water. The team used oxygen sensors in re-breathing bubbles to determine whether the lizard consumed oxygen from the bubbles. The researchers found that the concentration of oxygen in its bubbles decreased over time, supporting this view.
The discovery of different species of semi-aquatic lizards that have evolved to extract oxygen from the bubbles they breathe raises other exciting questions. For example, the longer a lizard dives, the lower the rate at which oxygen is consumed from the bubbles, which may be explained by the decrease in the mole’s metabolic rate as the dive time increases. Graduate co-author Alexandra Martin of Binghamton University is currently exploring whether body cooling during diving can help explain the phenomenon.
“Rebreathing has never been considered a potential natural mechanism for underwater breathing invertebrates,” said Luke Mahler, an assistant professor of EEB at the University of Toronto and a paper tutor at Boccia. “But our work shows that this is possible and that this lizard has repeatedly deployed this strategy in species that use aquatic habitats.”
Sverke and Mahler are planning future research projects to better understand the evolution of physiology and behavior associated with respiration. Anoles are a remarkable lizard population, and the number of diverse ways this group takes advantage of its environmental advantages is incredible.