A type of lizard that spends time both on land and in water has a unique way of breathing underwater by creating a bubble over its nostrils, which helps it avoid predators.
Meet the tiniest (and perhaps feistiest) scuba diver on the planet: a semi-aquatic lizard that generates a bubble above its nostrils to breathe while submerged, as revealed by new research conducted by Binghamton University, State University of New York.
Lindsey Swerk, an assistant research professor at Binghamton University, researches water anoles, a species of semi-aquatic lizard native to the tropical forests in southern Costa Rica. She previously observed these lizards using a bubble when they are beneath the water’s surface. When threatened by a predator, these lizards can dive underwater and utilize a bubble resting above their heads for respiration.
“We’ve established that they can remain submerged for a considerable duration and are drawing oxygen from this air bubble,” Swierk stated. “However, we weren’t certain if the bubble had a specific function related to respiration. Is it merely a consequence of their skin’s characteristics, a reflex related to breathing, or does this bubble genuinely extend the time they can stay submerged compared to without it?”
To determine whether the bubble plays a functional role in breathing or is just a byproduct, Swierk applied a substance on the lizards’ skin to inhibit bubble formation.
“Lizard skin repels water, which typically helps air cling tightly to it and form a bubble. But when an emollient covers the skin, air can no longer adhere, preventing bubble formation,” Swierk explained.
Swierk observed how many bubbles the lizards were able to create and how long they could hold their breath underwater, comparing these results with a control group of lizards who could breathe normally. She discovered that the control lizards could remain submerged for 32% longer than those with disrupted bubble formation.
“This finding is crucial because it is the first experiment to demonstrate the adaptive importance of the bubbles. Rebreathing bubbles enable the lizards to stay underwater longer. Previously, we only had suspicions based on observations; now we have evidence of its practical role,” said Swierk.
The research affirmed that the bubble is indeed advantageous for the lizards in prolonging their time underwater, which serves as a shelter from predators.
“Anoles are somewhat akin to the chicken nuggets of the forest; they’re preyed upon by birds and snakes,” Swierk remarked. “By diving into the water, they can evade many of these threats and remain very still while submerged. They are also quite well disguised underwater and can stay hidden until danger has passed. We know they can hold their breath for at least 20 minutes, and likely even longer.”
Looking ahead, Swierk aims to investigate whether the lizards utilize their bubble in a way similar to a physical gill, a mechanism seen in insects that enable them to breathe while underwater using air bubbles. However, because water anoles are relatively large, simply relying on oxygen diffusion from the surrounding water into the bubble may not be sufficient. One of Swierk’s graduate students, Alexandra Martin, is experimenting to see if this type of gill-like action can allow lizards to remain submerged even longer by altering the oxygen levels in the water and observing how this impacts their dive duration.
Swierk expressed excitement about the research, noting that understanding bubble use among vertebrates is still a largely unexplored area, which could lead to innovations in bioinspired materials. Additionally, exploring new animal behaviors is inherently intriguing.
“People have shared their passion for scuba diving and freediving with me and expressed curiosity about how animals might engage in similar activities,” said Swierk. “This opens a fantastic opportunity to ignite interest in science, connecting people’s hobbies with evolutionary adaptations observed in nature. It is remarkable how even common animals can surprise us with new findings.”
