An unusual underwater breathing behavior that had never before been seen in vertebrates was seen in a lizard by some researchers back in 2009. Unable to delve deeper into the topic, it slipped under the radar of evolutionary biologists until someone else reported a similar behavior a decade later. Now, in a new piece of research published in the journal Current Biology, those same researchers have finally been able to account for their observations in a study centered around Anolis lizards. Not only were they able to confirm that these lizards were using an underwater respiration technique previously only observed in arthropods, but they also found it was present in all six Anolis species they researched.
The impressive technique allows the lizards to stay underwater for a long time thanks to a bubble they exhale that clings to the skin on their nose. This air can then be re-inhaled in behavior the team has termed “rebreathing”, after the scuba-diving apparatus. "Rebreathing had never been considered as a potential natural mechanism for underwater respiration in vertebrates," said co-author Luke Mahler in a statement. "But our work shows that this is possible and that anoles have deployed this strategy repeatedly in species that use aquatic habitats."
Anolis lizards are a genus of anoles (famous for their flashy dewlap) in the family Dactyloidae and are native to the tropical Americas. Some within the genus are semi-aquatic, utilizing their impressive diving skills as a defense mechanism to avoid predators. Upon submerging, they release the air bubble for rebreathing which can sustain them underwater for up to 18 minutes. The team was able to confirm that this was due to rebreathing as they could measure the bubbles’ oxygen content, which decreased over time.
The key to the remarkable rebreathing is not this diving, according to the researchers, but most likely the anoles’ hydrophobic skin structure. “All anole lizards have water-resistant skin,” Mahler told IFLScience. “As a result, even species that don’t dive during the normal course of their lives will develop a thin film of air over their scales if you dip them in water (giving them a “quicksilver” appearance). We still have much to learn about what makes anole skin so waterproof. It likely has to do with the structure and arrangement of the scales, but we don’t know that yet for sure."
A video filmed by Day’s Edge Productions (who worked with the researchers) gives a decent idea as to why this behavior evolved. When threatened by approaching camera operators, the anoles swiftly hurled themselves into the air before splashing down in the water. Being able to remain submerged for a long time was likely a boon for survival, as predators might get bored and move on rather than wait out the bubble.
“As for the leap, that’s simply a nice healthy escape response," Mahler said. "They’re good jumpers, which is frustrating when you’re trying to study them! This impressive leap was probably in response to an approaching scientist or camera-person.”
An incredible evolutionary feat, but one we imagine was a real pain in the butt to study, photograph and film. So, what was it all for? Beyond its academic value to evolutionary biologists, it’s possible the mechanisms that underpin this rebreathing behavior could be harnessed for human innovations, such as the rebreather scuba-diving apparatus the behavior was named after. But, as Mahler explained, reaching detailed and applicable insights will first require physiological experiments in a lab setting.