Diving lizards breathe air with bubbles on the muzzle


With a GoPro and a little patience, biology professor Lindsey Swierk discovered an Anolis lizard from Costa Rica in 2019 deploying a bubble horn to its muzzle underwater. The reptile was not preparing for combat, but rather to “breathe” the air it exhaled which became trapped in an invisible layer between its skin and the surrounding water.

The intelligent re-inhalation of precious oxygen, a feat that can last up to 16 minutes, mimics the technology used by scuba divers – thus the diving lizard was born.

Two years later, a team of evolutionary biologists learned that several distantly related semi-aquatic anole species were executing this same survival strategy. This suggests for the first time that these lizards are repeatedly evolving the specialized breathing technique, which likely improves diving performance by allowing rapid absorption of oxygen from the water.

Not to mention that prolonged time spent underwater helps protect reptiles from predators, according to the study published May 12 in the journal Current Biology.

“Rebreathing has never been considered a potential natural mechanism for underwater respiration in vertebrates,” Luke Mahler, assistant professor of ecology and evolutionary biology at the University of Toronto, said in a statement. “But our work shows that it is possible and that anoles have deployed this strategy on several occasions in species that use aquatic habitats. “

The discovery that different species of anoles “converged during evolution” to breathe underwater using rebreathed air bubbles also raises other “exciting” questions, added Lindsey Swierk, co -author of the study with Binghamton University in New York.

“For example, the rate of oxygen uptake of the bubble decreases the longer an anole dives, which could possibly be explained by a reduction in the metabolic rate of one anole,” Swierk said in the release.

The team carried out experiments on 20 species of Anolis lizards (three or more adult lizards in each group), including five semi-aquatic. Researchers have discovered the breathing technique of scuba diving in 18 species, with the majority of lizards of all semi-aquatic species showing off their bubble horns.

Sustained breathing – five or more breaths per trial – occurred in 12 of the species tested, but mainly among the semi-aquatic.

The strategy works because lizards have hydrophobic skin that repels water, allowing “dead space air” between the skin and surrounding water to enter the lungs via a tiny bubble stuck to their skin. muzzle, similar to the way fish breathe with gills.

To test whether the lizards were really extracting oxygen from their bubble horns, the team placed oxygen sensors inside them. As it turns out, oxygen levels continued to drop as the lizard spent time underwater, “like a real scuba tank.”

Researchers believe that the special skin of anoles may be exaptive, meaning that it has been adopted repeatedly over generations for a purpose (underwater breathing) other than that for which it was designed.

The team is now testing additional theories that could explain the behavior, such as whether body cooling during dives plays a role.

“Anoles are a remarkable group of lizards,” Swierk said, “and the number of ways this taxon has diversified to take advantage of their environment is mind-boggling.”

A separate study published last year found that some anole species developed larger pads after hurricanes compared to those that had not experienced an intense storm. It was the first article to indicate that hurricanes act as an agent of natural selection.

Katie Camero is a McClatchy National Real-Time Science reporter. She is a Boston University alumnus and has reported for the Wall Street Journal, Science and The Boston Globe.

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