Nature’s scuba tanks? Researchers discover how the lizard Anolis breathes underwater

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A team of evolutionary biologists from the University of Toronto has shown that Anolis lizards, or anoles, are able to breathe underwater using a bubble attached to their snout.

Anoles are a diverse group of lizards found in the tropical Americas. Some anoles are flow specialists. Semi-aquatic species frequently dive underwater to avoid predators, where they can remain submerged for up to 18 minutes.

“We have found that semi-aquatic anoles exhale air in a bubble that clings to their skin,” explains Chris Boccia, alumnus of the Department of Ecology and Evolutionary Biology of the Faculty of Arts and Sciences.

Chris Boccia is a recent Masters of Science graduate from the Department of Ecology and Evolutionary Biology in the Faculty of Arts and Sciences (photo courtesy of Chris Boccia)

“The lizards then re-inhale the air, a maneuver we have called ‘rebreathing’ after scuba diving technology.”

Boccia is the lead author of an article describing the discovery published in the journal Current biology.

The researchers measured the oxygen content of the air in the bubbles and found that it decreased over time, confirming that the air breathed was involved in breathing. Rebreathing likely evolved because the ability to stay submerged for longer increases the lizard’s chances of escaping predators, the authors say.

The authors studied six species of semi-aquatic anoles and found that all of them possessed the trait of respiration, although most of the species are distant. Although rebreathing has been widely studied in aquatic arthropods such as aquatic beetles, it was not expected in lizards due to physiological differences between arthropods and vertebrates.

“Rebreathing had never been considered a potential natural mechanism of underwater respiration in vertebrates,” says Luke mahler, assistant professor in the department of ecology and evolutionary biology and thesis director of Boccia.

“But our work shows that it is possible and that anoles have deployed this strategy on several occasions in species that use aquatic habitats.

Luke Mahler is Assistant Professor in the Department of Ecology and Evolutionary Biology (photo courtesy of Luke Mahler)

Mahler and co-author Richard Glor, University of Kansas, first observed breathing anoles in Haiti in 2009, but were unable to perform any other observations or experiments. . Another co-author, Lindsey Swierk, of Binghamton University, State University of New York, described the same behavior in a Costa Rican species in 2019. These early observations suggested that rebreathing was an adaptation for diving, but this idea had not been tested before now.

Boccia says he became interested in aquatic anoles after meeting one in Panama. He started his rebreathing investigations in Costa Rica in 2017 and continued his research in Colombia and Mexico.

As the authors note, the rebreathing trait may have developed because the skin of the anoles is hydrophobic – it repels water – a characteristic that likely evolved in the anoles because it protects them from rain and parasites. Underwater, air bubbles cling to the hydrophobic skin and the ability to harness these bubbles for breathing has developed as a result.

While more work is needed to understand how the process works in detail, Boccia, Mahler, and their coauthors suggest different ways in which rebreathing can work.

In its simplest form, the air bubble on a lizard’s snout likely acts as a diving tank, providing a submerged animal with a supply of air in addition to the air in its lungs. This is what aquatic arthropods like aquatic beetles do to extend the duration of their immersion.

Researchers also suggest that the rebreathing process may make it easier to use air found in a lizard’s nasal passages, mouth, and windpipe that otherwise would not be used by the lizard for breathing.

The bubble can also help rid waste carbon dioxide (CO2) from exhaled air through a process other researchers have observed in aquatic arthropods. These studies concluded that because CO2 is highly soluble in water and the level of CO2 in bubbles is higher than in the surrounding water, the exhaled CO2 dissolves in the surrounding water instead of dissolving in the surrounding water. ‘to be re-inhaled.

Finally, the authors speculate that the bubble can act as a gill and absorb oxygen from the water – again, something that has already been observed in arthropods. Boccia and Mahler are planning further research to confirm whether these rebreathing processes occur with anoles.

“This work enriches our understanding of the creative and unexpected ways in which organisms cope with the challenges posed by their environment,” says Mahler. “This is valuable in itself, but discoveries like this can also be valuable to humans as we seek solutions to our own difficult problems.”

“It is too early to say if the rebreathing of lizards will lead to any particular human innovations,” Boccia says. “But rebreathing biomimicry may be an interesting proposition for several areas – including rebreathing scuba diving technology, which has motivated our naming of this phenomenon.

The research was funded by the Natural Sciences and Engineering Research Council of Canada, among others.

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