‘Chicken nugget of the forest’ uses air bubble to stay underwater, avoid predators

According to new research from Binghamton University, the Anolis aquaticus , a scuba-diving tropical lizard from Central America, can breathe underwater. A special bubble is released through its nostrils, which clings to its head.

Water anoles have been well-documented, as Lindsey Swierk, senior author of the observational study just published in Biology Letters , stated.

“We know that they can stay underwater for a really long time, that they’re pulling oxygen from this bubble of air,” Swierk said. “We didn’t know whether there was actually any functional role for this bubble in respiration.”

“Is it something that lizards do that is just a side effect of their skin’s properties or a respiratory reflex, or is this bubble actually allowing them to stay underwater longer than they would, say, without a bubble?”

To answer the question, Swierk conducted an experiment to first understand this intriguing mechanism more deeply which she hopes will one day lead to the development of new biomaterials.

“The chicken nuggets of the forest” need to escape—fast

Lindsey Swierk described anoles as “kind of like the chicken nuggets of the forest.” As a sought-after snack, water anoles must avoid danger from the skies as well as on the ground. So they developed an impressive strategy that enables them to throw themselves into the water quickly and stay there until the threat leaves.

The air bubble allows the camouflaged water anole to remain underwater “for a really long time,” Swierk said in a press release. Longer than 20 minutes.

But Swierk didn’t know whether the bubble was a by-product of a respiratory function or whether it permitted lizards to breathe underwater. To investigate the bubble that renders this lizard a scuba diver further, Swierk applied a substance to its skin that prevented the bubble from sticking to its head.

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

After splitting the water anoles into two groups, some were allowed to breathe normally whereas a select few had their bubble-making capacity impaired. As a result, Swerk just proved that the bubble enabled lizards to stay underwater 32% longer than those with impaired bubble formation.

“This is really significant because this is the first experiment that truly shows the adaptive significance of bubbles. Rebreathing bubbles allow lizards to stay underwater longer. Before, we suspected it – we saw a pattern – but we didn’t actually test if it served a functional role,” Swierk explained.

Is the bubble a physical gill?

Next, Swierk plans to assess whether the bubbles act as a physical gill for the lizard . Insects, for example, use bubbles to breathe underwater, but they don’t require that much oxygen. She suspects that the water anole is too big to sustain itself only with the air in the bubble.

One of Swierk’s graduate students, as per the press release , is currently testing whether a physical gill-type action is allowing lizards to spend even more time underwater by changing the oxygenation of the water and measuring its effects on lizards’ dive time.

As nature’s mechanisms inspire scientists to replicate them, this research “is exciting,” according to Swierk. Little is known about vertebrate bubble use currently, and it could lead to the development of bioinspired materials. “It’s also just interesting to learn about new animal behavior.”

“I’ve had people talk to me about how much they love scuba diving and freediving and how they’re interested in how animals might do the same thing,” Swierk concludes.

“So there’s a great opportunity to get people excited about science by having this relationship between what they love to do and what’s evolved in nature. Even in animals that seem commonplace – you’re always finding new things.”

The paper, “Novel rebreathing adaptation extends dive time in a semi- aquatic lizard ,” was published in Biology Letters .