Nature never ceases to amaze. Right when you think you've seen it all, researchers discover a scuba-diving lizard, reports Phys.org.
Researcher Lindsey Swierk of Binghamton University, State University of New York, first caught wind of this amphibious behavior while hiking along mountain streams on a research trip in Costa Rica. She noticed that when local water anoles (Anolis aquaticus) were startled, they dove into the water to hide, and they stayed underwater for unusually long periods of time, up to 16 minutes.
Curious, Swierk decided to submerge an underwater camera to spy on these free-diving reptiles, to see how they might be managing to hold their breaths for so long. What she discovered was unlike anything she'd seen before. The lizards appeared to be generating a bubble atop their heads that acted like oxygen tanks, allowing them to bring air with them as they waited underwater.
"Finding evidence suggesting that water anoles 'breathe' under water was serendipitous, and not part of my original research plan," said Swierk. "I was impressed and pretty confused about the length of the dive, which gave me an itch to take a closer look with an underwater camera in the next couple of years. That's when I saw that the anoles appeared to be rebreathing a bubble of air that covered their heads."
How does the air bubble work?
Swierk's video is the first to observe this scuba diving behavior in action, and it's remarkable to witness. Researchers haven't figured out exactly how the anoles generate the bubble yet, but they suspect the shape of the lizard's head may have evolved to influence bubble formation. It's also unclear how the air bubbles work, but there are theories.
"I think it's possible that some additional air pockets are being trapped around the anole's head and throat, and that the inhalation and exhalation of the air bubble allow for some trading of fresh air among these air pockets, allowing the anole to swap air in its current air bubble with 'new' air," said Swierk. "It's additionally possible that the air bubble plays a role in allowing an anole to get rid of carbon dioxide. I suspect that there might be morphological adaptations, namely the shape of the top of the anole's head, which allows a large bubble of air to cling to it easily."
Additional study of these anoles has shown that their stomach contents include a healthy percentage of insects that are aquatic, suggesting they might be utilizing their time underwater for more than just hiding from predators. They appear to be predators themselves.
The next step will be to definitively answer these questions about this intriguing lizard with a secret underwater life, and also to see if other related anoles might have evolved similar adaptations.
"If future investigation reveals that this rebreathing behavior is adaptive, then I would imagine that it is a trait that evolved over time to allow water anoles, and perhaps similar anole species, to thrive in their aquatic habitats," said Swierk.