‘Scuba-diving’ lizards are real — and here’s why their underwater trick is special
With a GoPro and some patience, biology professor Lindsey Swierk discovered a Costa Rican Anolis lizard in 2019 deploying a bubble horn on its snout underwater. The reptile wasn’t preparing for battle, but rather “rebreathing” air it exhaled that got trapped in an invisible layer between its skin and surrounding water.
The clever re-inhaling of precious oxygen, a feat that can last up to 16 minutes, mimics technology used by scuba divers — thus the scuba-diving lizard was born.
Two years later, a team of evolutionary biologists learned several distantly related semi-aquatic anoles species perform this same survival strategy. This suggests for the first time that these lizards repeatedly evolve the specialized breathing technique, which likely improves dive performance by allowing the swift uptake of oxygen from water.
Not to mention, prolonged time spent underwater helps protect the reptiles from predators, according to the study published May 12 in the journal Current Biology.
“Rebreathing had never been considered as a potential natural mechanism for underwater respiration in vertebrates,” Luke Mahler, an assistant professor of ecology and evolutionary biology at the University of Toronto, said in a statement. “But our work shows that this is possible and that anoles have deployed this strategy repeatedly in species that use aquatic habitats.”
The finding that different species of anoles “have evolutionarily converged” to breathe underwater using rebreathed air bubbles points to other “exciting” questions, too, study co-author Lindsey Swierk with Binghamton University in New York added.
“For example, the rate of oxygen consumption from the bubble decreases the longer an anole dives, which could possibly be explained by a reduction in an anole’s metabolic rate,” Swierk said in the statement.
The team conducted experiments on 20 Anolis lizard species (three or more adult lizards in each group), including five semi-aquatic ones. Researchers discovered the scuba-diving breathing technique among 18 species, with the majority of lizards in 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 mostly among the semi-aquatics.
The strategy works because the 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 glued to their snouts, similar to how fish breathe with gills.
To test if the lizards were truly extracting oxygen from their bubble horns, the team placed oxygen sensors inside of them. Turns out oxygen levels continued to drop the longer the lizard spent submerged underwater, “in true scuba-tank fashion.”
Researchers speculate anoles’ special skin may be exaptative, meaning it was repeatedly adopted across generations for a purpose (underwater breathing) other than the one it was built for.
The team is now testing additional theories that might 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 that this taxon has diversified to take advantage of their environments is mind-boggling.”
A separate study published last year found that some anole species developed larger toepads after hurricanes compared to those that didn’t experience an intense storm. It was the first paper to indicate hurricanes act as an agent of natural selection.
This story was originally published May 26, 2021 at 4:28 PM with the headline "‘Scuba-diving’ lizards are real — and here’s why their underwater trick is special."
