The water anole is a small, olive-brown lizard that is fairly unremarkable at first glance. However, it’s developed a type of superpower using the water around its habitat.
These lizards often find themselves needing to escape predators, such as birds or crabs, and the quickest getaway is often to dive straight into a stream. But instead of simply holding their breath like other animals, water anoles have learned to manipulate bubbles of air in a way that allows them to “breathe” underwater.
A lizard scuba tank
Unlike their cousins that bask in trees or scuttle on the forest floor, water anoles spend much of their time near the water’s edge, where they hunt for insects and other small prey.
For a creature that lives so close to water, it would seem necessary to develop some form of aquatic prowess. The water anole has done just that. It’s evolved not only the ability to swim but also a remarkable mechanism to remain submerged for longer than most reptiles can manage. When the lizards feel threatened, they jump underwater and blow a bubble.
This bubble acts like a makeshift scuba tank. Research conducted by Lindsey Swierk, a behavioral ecologist from Binghamton University, observed water anoles staying submerged for at least 16 minutes — far longer than most animals their size could manage. The key to this feat lies in their ability to extract oxygen from the air trapped in these bubbles.
“We know that they can stay underwater for a really long time. We also know that they’re pulling oxygen from this bubble of air,” said Swierk, then added, “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 allowing them to stay underwater longer than they would, say, without a bubble?”
Aquatic Adaptation
The phenomenon works due to a combination of physical properties. Water anoles have hydrophobic (water-repellent) skin. This hydrophobicity allows a thin layer of air to cling to their bodies. When submerged, the anole can re-inhale from this air layer, extending the amount of time it can stay underwater. Essentially, the anole’s skin functions like a scuba mask, keeping a supply of breathable air close at hand.
To confirm whether the bubble helps the lizards breathe, Swierk and colleagues applied a substance to the lizards’s skin that prevented the bubble formation.
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“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,” said Swierk.
They did this to see whether the lizards would stay underwater a shorter time — and they did. Compared to a control group, they stayed underwater for 32% less time, showing that without the bubble, they couldn’t hold their breath as long.
“This is really significant because this is the first experiment that truly shows 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,” said Swierk.
A Unique Evolved Strategy
This research provides the first experimental evidence that water anoles use air bubbles to extend their time underwater for survival, confirming that the bubbles serve a functional role in respiration. Previously, scientists only suspected this adaptive behavior based on observations, but Swierk’s experiment, which prevented the bubble formation, demonstrated that without the bubbles, the lizards could not stay submerged as long. This discovery is crucial for understanding how these lizards have evolved such a specialized survival mechanism, helping them escape predators in aquatic environments where breathing is typically limited.
Beyond its implications for evolutionary biology, this research could have broader applications in biomimicry and technology. The water anole’s ability to extract oxygen from a trapped air bubble hints at potential innovations in underwater breathing systems for humans, or even in designing materials and structures that mimic the lizard’s hydrophobic skin.
By showing how a small lizard can manipulate the physical properties of water and air to its advantage, this study opens new avenues for understanding the intersection of biology, physics, and technology.
“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,” said Swierk. “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.”