Presenting the world’s smallest (and dirtiest) diver: A species of semi-aquatic lizard produces a special bubble over its nostrils to breathe underwater and avoid predators, according to new research from Binghamton University, State University of New York.
Lindsey Swerk, assistant research professor of biological sciences at Binghamton University, studies water anoles, a type of semi-aquatic lizard found in the tropical forests of southern Costa Rica. She had previously documented the lizards using an underwater bubble. When these lizards feel threatened by a predator, they dive underwater and breathe a bubble above their heads.
“We know that they can stay under water for a very long time. We also know that they get oxygen from this air bubble,” says Swierk. “We didn’t know if this bubble actually played a functional role in breathing. Is it something lizards do that is just a side effect of the properties of their skin or a breathing reflex, or does this bubble allow them to stay underwater for longer? than they would, for example, without a bubble?”
To investigate whether the bubble plays a functional role in breathing or is just a byproduct, Swierk applied a substance to the skin surface of the lizards that would prevent bubble formation.
“A lizard’s skin is hydrophobic. This allows the air to stick very tightly to the skin and this air bubble to form. But if you cover the skin with an emollient, the air no longer sticks to the skin’s surface, so the air bubbles can no longer form.” shape,” says Swierk.
Swierk recorded the number of bubbles the lizards could produce and how long they could stay underwater, and compared them with lizards in a control group that were allowed to breathe normally. She discovered that the lizards in the control group were able to stay underwater 32% longer than the lizards with reduced bubble formation.
“This is really important because this is the first experiment to really demonstrate the adaptive significance of bubbles. Re-breathing bubbles allows lizards to stay underwater longer. We used to suspect it – we saw a pattern – but we didn’t really test whether it fulfilled a functional role,” says Swierk.
The study confirmed that the bell lizards help them stay underwater for longer periods of time, giving them a refuge from predators.
“Anoles are kind of like the chicken nuggets of the woods. Birds eat them, snakes eat them,” Swiek said. “So by jumping into the water, they can escape many of their predators, and they stay very still underwater. They are also quite well camouflaged underwater, and they just stay underwater until the danger has passed. We know that They can stay underwater for at least about 20 minutes, but probably longer.”
In the future, Swierk wants to find out whether lizards use the bell as something called a physical gill. A physical gill occurs in insects that use bubbles to breathe underwater. Insects have a lower oxygen requirement and the amount of oxygen diffusing from the water into the air of the bubble is sufficient to sustain them. Water anoles are probably too large to be supported solely by the oxygen diffusing into a bubble. One of Swierk’s graduate students, Alexandra Martin, is testing whether a physical gill-like action allows lizards to spend even more time underwater by changing the oxygenation of the water and measuring its effects on lizards’ diving time.
Swierk said the research is exciting because scientists don’t know much about the use of bubbles in vertebrates, which could open the door to bio-inspired materials. It’s also just interesting to learn about new animal behavior.
“I’ve had people talk to me about how much they love diving and freediving, and how they’re interested in how animals could do the same,” Swierk said. “So there’s a great opportunity to get people excited about science by having this relationship between what they like to do and what has evolved in nature. Even in animals that seem mundane, you’re always discovering new things.”
