“Diving” lizards use bubbles to breathe underwater and avoid predators

Meet the world’s smallest (and clumsiest) scuba diver: A species of semi-aquatic lizard produces a special bubble above its nostrils to breathe underwater and avoid predators, according to new research from Binghamton University, State University of New York.

Lindsey Swerk, a research assistant professor of biological sciences at Binghamton University, studies water anoles, a type of semi-aquatic lizard found in the rainforests of southern Costa Rica. She had previously observed these lizards using an underwater bubble. When these lizards feel threatened by a predator, they dive underwater and blow a bubble over their heads.

“We know they can stay underwater for a very long time. We also know they get oxygen from this air bubble,” Swierk said. “We didn’t know if this bubble plays a functional role in respiration. Is this something that lizards do that’s just a side effect of their skin properties or a respiratory reflex, or does this bubble allow them to stay underwater longer than they would, for example, without a bubble?”

To determine whether the bubble plays a functional role in respiration or is merely a byproduct, Swierk applied a substance to the surface of the lizards’ skin that would prevent bubble formation. The paper, “Novel rebreathing adaptation extends dive time in a semi-aquatic lizard,” was published in Biology letters.

“Lizard skin is hydrophobic. Typically, that allows air to stick very tightly to the skin and that bubble to form. But when you coat the skin with an emollient, the air no longer adheres to the surface of the skin, so the bubbles can’t form,” Swierk said.

Swierk recorded the number of bubbles the lizards could produce and how long they could stay underwater, and compared them to those in a control group that was allowed to breathe normally. She found that the lizards in the control group could stay underwater 32 percent longer than those whose bubble formation was impaired.

“This is really important because this is the first experiment that really shows the adaptive importance of bubbles. Breathing bubbles allow lizards to stay underwater longer. Before, we suspected this – we saw a pattern – but we hadn’t really tested whether it played a functional role,” Swierk said.

The study confirmed that the bubble helps the lizards stay underwater longer, providing them with refuge from predators.

“Anoles are kind of like the chicken nuggets of the forest. Birds eat them, snakes eat them,” Swiek says.

“By jumping into the water, they can escape many of their predators and remain very still underwater. They are also quite well camouflaged underwater and will stay underwater until the danger has passed. We know they can stay underwater for at least 20 minutes, but probably longer.”

In the future, Swierk wants to determine whether the lizards use the bubble as a kind of physical gill. Insects that use bubbles to breathe underwater have a physical gill. Insects have lower oxygen requirements, and the amount of oxygen that diffuses from the water into the air in the bubble is enough to sustain them.

Aquatic anoles are probably too large to be sustained solely by the oxygen that diffuses into a bubble. One of Swierk’s graduate students, Alexandra Martin, is testing whether a gill-like physical action allows the lizards to spend even more time underwater by altering the oxygenation of the water and measuring its effects on the lizards’ diving time.

Swierk said the research is exciting because scientists don’t know much about using vertebrate bubbles, which could open the door to bio-inspired materials. It’s also exciting to learn about a new animal behavior.

“People have told me about their passion for scuba diving and freediving, and their interest in how animals might do the same thing,” Swierk said. “So there’s a great opportunity to get people interested in science by making that connection between what they love to do and what’s evolved in nature. Even with seemingly mundane animals, you’re always discovering new things.”