Lizard makes its own “oxygen tank” to breathe underwater

In a Costa Rican rainforest, a small semiaquatic lizard known as the water anole jumps into a stream. Minutes pass, but the anole does not emerge to breathe, as lizards normally do.

Instead, the lizard settles on a rock in the riverbed with a small air bubble on top of your head which expands like a balloon and then shrinks. Just like a diver, the reptile is breathing underwater with a stored oxygen reservoir .

Using this air bubble helps the anole extend its stay underwater, according to Dr. Lindsey Swierk, assistant research professor of biological sciences at Binghamton University in New York.

Images Swierk recently captured of submerged anoles show prominent bubbles inflating and deflating on the reptiles’ heads. This technique may help anoles hide from predators on land, Swierk reported Tuesday. in the journal Biology Letters.

Swierk has been studying aquatic anoles for nearly a decade, and in 2021 he teamed up with other researchers to describe bubble breathing behavior in several species of semiaquatic lizards in the genus Anolis.

“A lot of the collaborations came out of some very basic questions — a lot of us watching these videos, wondering how does this happen, why does this happen,” she told CNN.

For the new study, Swierk investigated the species Anolis aquaticus, which lives near forested streams in southwestern Costa Rica and western Panama. She found that bubble formation directly affected how long an anole could stay submerged.

During the experiments, the bubble-breathing anoles remained underwater for an average of 3.5 minutes, about 32 percent longer than anoles that were prevented from forming air bubbles by applying an emollient to parts of their heads.

“They can prolong their dives using these breathing bubbles,” Swierk said.

Water anoles are not fast runners and rely primarily on camouflage to hide from predators such as birds, snakes, mammals and other lizards. And when camouflage fails, waiting for the threat to pass underwater is an effective survival strategy, Swierk explained.

“A fascinating behavior”

Trapping air in bubbles to breathe underwater is a practiced by some types of insects and arachnids, such as water beetles and diving bell spiders. So far, anoles are the only animals with backbones known to breathe using bubbles.

“This is a fascinating behavior in lizards,” said Dr. Earyn McGee, a lizard herpetologist and conservation engagement coordinator at the Los Angeles Zoo. “This type of research will increase our understanding of how these lizards and possibly other animals evolved their underwater breathing techniques.”

To get a closer look at the anoles’ bubble breathing method, Swierk collected animals of the species Anolis aquaticus at the Las Cruces Biological Station in Costa Rica. Their destination was a nearby “arena” — a clear plastic tank containing stream water and rocks.

In one group of anoles, the researchers coated the reptiles’ snouts and heads (avoiding covering the nostrils) with a thin layer of moisturizing emollient to prevent air bubbles from adhering to the anoles’ heads. The scientists then submerged the anoles and filmed them in the arena until they emerged.

In the control group without moisturizer, all of the anoles produced large bubbles that they repeatedly used to breathe, at a rate of about six per minute. Some anoles in the emollient-treated group also produced bubbles, but they were much smaller and did not stick to the lizards’ skin like air bubbles that could be inhaled.

In both groups, the anoles performed a throat pumping action called gular pumping, which many types of lizards use to supplement their lungs with oxygen.

For diving anoles, gular pumping may also play a role in circulating stored oxygen, affecting how long anoles can stay underwater. But in experiments, hydrated anoles that couldn’t produce oxygen-filled bubbles surfaced 67 seconds sooner than those that used bubbles to breathe.

However, this diving tactic has a downside.

“One of the costs of diving is that they get very cold,” Swierk said. Mountain streams are typically cold, and as ectotherms, anoles regulate their body temperature through their environment.

“They pay a temperature cost when they dive,” she said. Being too cold “could reduce their ability to run quickly, defend their territories against invaders, court mates or digest their food.”

Another downside could be that if a submerged lizard is still visible, a predator might simply wait for it to resurface, McGee said.

“Lizards can only stay underwater for so long,” she said. “How does the lizard know when it’s safe to come out — or do they just use up all the air and then emerge?”

The mechanism of anoles’ bubble breathing is something Swierk hopes to understand through collaborations with several research groups. One part of the puzzle is whether the shapes of anoles’ heads or the microscopic structures in their scales affect the volume of air that fills their bubbles. Another unsolved question is how diving anoles store and circulate oxygen while underwater.

“As far as we know now, the oxygen that the lizard is using, it takes underwater with it,” Swierk said. That oxygen could be stored in its lungs, elsewhere in its respiratory system or in air sacs attached to its skin, which are then incorporated into the head bubble.

Oxygen could also diffuse into the bubble from the water. “But we don’t know that for sure,” Swierk added. “We’re still working on that.”

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This content was originally published in Lizard makes its own “oxygen tank” to breathe underwater on the CNN Brasil website.

Source: CNN Brasil

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