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In the rain forest of Costa Rica, a small aquatic lizard called a “diving anole” jumps into a stream. Minutes pass, but the anole doesn’t come up for air, as these lizards do. Instead, an underwater lizard is lying on a river rock, a small air bubble on top of its head expanding like a balloon and then shrinking. Like a diver, this reptile breathes a pool of stored oxygen.
Using this bubble helps anoles prolong their stay underwater, according to Dr. Lindsey Swierk, assistant professor of biological sciences at Binghamton University, New York. Swierk’s recent photographs of anoles underwater show prominent swelling and collapse on the reptiles’ heads. This technique may help anoles hide from predators in the wild, Swierk reported Tuesday in the journal Biology Letters.
Swierk has studied diving anoles for nearly a decade, joining in 2021 with other researchers to describe the behavior of bubble breathing across several species of semiaquatic lizards in the Anolis genus.
“A lot of the interactions have come from some basic questions — a lot of us are watching these videos, wondering how it’s happening, why it’s happening,” he told CNN.
For the new study, Swierk investigated the species Anolis aquaticus, which lives near forest streams in southwestern Costa Rica and western Panama. Swierk found that the shape of the bubble directly affects how long an anole can stay submerged. During the tests, the bubble-breathing anoles stayed underwater for an average of 3 ½ minutes. It was about 32% longer than the anoles that were prevented – by the use of an emollient on parts of their heads – from making air bubbles.
“They can prolong their dive by using these breathing tubes,” Swierk said.
Diving anoles are not fast runners and mainly rely on hiding to hide from predators such as birds, snakes, mammals and other lizards. And when hiding fails, waiting for the threat underwater is an effective survival strategy, Swierk said.
Air trapping for underwater breathing is used by some types of insects and arachnids, such as water beetles and diving spiders. To date, anoles are the only vertebrates known to breathe through bubbles.
“This is an amazing behavior of lizards,” said Dr. Earyn McGee, a lizard herpetologist and conservation coordinator at the Los Angeles Zoo. “This kind of research will increase our understanding of how these lizards and possibly other animals evolved their underwater breathing techniques.”
To study the anoles’ bubble breathing technique, Swierk collected A. aquaticus anoles at the Las Cruces Microbiology Center in Costa Rica. Their destination was a nearby “arena” – a clear plastic tank with stream water and rocks. In one group of anoles, the researchers covered the reptiles’ noses and heads (avoiding the noses) with a thin absorbent pad to prevent air bubbles from sticking to the anoles’ heads. After that, the scientists submerged the anoles and took them into the playground until they emerged.
In the non-humidified control group, all the anoles produced large bubbles that they inhaled frequently, at a rate of about six per minute. Some anoles in the emollient-treated group also produced bubbles, but they were very small and did not stick to the lizards’ skin, as the breathing air bubbles did. do. In both groups, anoles performed a throat-pumping process called gular pumping, which many lizard species use to supplement their lungs with oxygen.
For diving anoles, constant pumping can also play a role in circulating stored oxygen, which affects how long anoles can stay underwater. But in tests, humid anoles that couldn’t produce oxygen-filled bubbles emerged 67 seconds faster than those that used bubbles to breathe.
However, this trick like scuba has its problems.
“One of the costs of diving is that they are very cold,” Swierk said. Mountain streams are often cold, and as ectotherms, anoles regulate their body temperature in their environment.
“They pay a thermal cost when they dive,” he said. Extreme cold “could reduce their ability to run fast, defend their territory from predators, court mates, or digest their food.” .”
Another drawback may be that if an underwater lizard remains visible, the predator may be waiting for it to resurface, McGee said.
“Lizards can be submerged for so long,” he said. “How does a lizard know when it’s safe to come out – or does it use up all its life, and then come back out?”
The bubble breathing mechanism of anoles is something Swierk hopes to piece together in collaboration with multiple research groups. Another part of the game is how the shapes of the anoles’ heads or the very small shapes in their scales affect the sound of the 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 uses, it takes underwater as well,” Swierk said. That oxygen can be stored in its lungs, in other parts of the respiratory system or in air pockets attached to its skin, and then absorbed into the bubble of the head.
Oxygen may also enter the bubble from the water, “but we don’t know that for sure,” Swierk added. “We’re still working on that.”
Mindy Weisberger is a science writer and content producer whose work has appeared in Live Science, Scientific American and How It Works magazine.
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