A special lizard called the water anolis lives in the tropical forests of Costa Rica. This small but brave reptile has developed a unique way of breathing underwater: it knows how to produce an air bubble that stays above its nose.
outside New search by Binghamton University In New York, this trick appears to allow the animal to stay in place for long periods and thus escape hungry predators.
Diving Lizard: Bubble Trick
Lead researcher Lindsay Swirk previously discovered that anoles use an air bubble when they feel threatened. Once a predator approaches, the lizards dive into the water and breathe through an air bubble that forms above their nose. “We know that they can stay underwater for a very long time,” Swirk says. “And that they extract oxygen from that air bubble. But we didn’t know if that bubble actually played a functional role in their breathing or was just a byproduct of their waterproof skin. But now it seems that anoles can stay underwater for longer because of the air bubble on their nose.”
Bullying a lizard in the name of science
To see if the air bubble really did help with breathing, Swierk decided to conduct a rather bleak experiment. She applied a special ointment to the lizards’ skin to prevent air bubbles from forming. Anoles’ skin is normally water-repellent, so air can easily stick to their skin. But with the new coating, this was no longer possible. Swierk then compared how long the lizards could stay underwater with and without the air bubble. The results were clear: lizards with an air bubble on their noses stayed underwater 32 percent longer than their counterparts without an air bubble.
“This is an important discovery, because this is the first experiment that really proves that the bubble provides an evolutionary advantage,” explains Swierk. “We already had our suspicions, but now we’ve tested it and proven it: this bell helps the lizard stay underwater longer and allows it to better escape predators.”
Chicken nuggets from the woods
Water anoles are a popular snack for many predators. “You could say they’re the chicken of the woods,” says Swierk. “Birds eat them with relish, and snakes will eat lizards one by one if they get the chance.” However, by diving into the water they can avoid many of these predators. They remain very still underwater, making them difficult to see. “We know they can stay underwater for at least 20 minutes, but probably longer.”
physical gills
The research also raises new questions. For example, Swirk wants to see if the water anolis uses the air bubble in the same way that insects use physical gills. Physical gas gills are simple bells that attach to water-dwelling insects or their larvae. In some insects, this air bubble ensures that enough oxygen is exchanged with the water to allow them to breathe continuously underwater. Our Costa Rican lizard doesn’t have that luxury, because reptiles need more oxygen than insects. But it’s possible that some oxygen exchange also occurs in the nasal bubble of water anoles. One of Swirk’s students is testing whether the bell can influence the oxygen level in the water and thus prolong dive time.
Bio-inspired materials
This is an exciting area of research for scientists, especially since little is known about the use of air bubbles in vertebrates. Furthermore, the research could provide inspiration for new bio-inspired materials. But for Swirk, it’s exciting to discover a new form of animal behavior. “People often talk about how they love scuba diving or freediving,” Swirk explains. “And they’re curious about how animals do it. It’s a great opportunity to get people interested in science by showing that animals sometimes develop behaviors that bear a lot of similarities to things we love.”
