Various species of aquatic insects, such as the predaceous diving beetle, use bubbles for breathing underwater. Now, in a first-of-its-kind discovery, biologists have found that several species of anole, a mini tropical tree-dwelling lizard, also evolved to "breathe underwater," reports Douglas Main for National Geographic. The study was published in Current Biology this month.
The semi-aquatic anoles are found near streams across Latin America and the Caribbean. When frightened, anoles will jump from trees or rocks and plunge into the water below. Once submerged, the lizards exhale and create a giant bubble that sticks to the edge of their snouts, National Geographic reports. Scientists suspect the anoles evolved this tactic to breathe underwater while escaping predators and foraging for food.
Researchers placed six different anole species into tanks filled with water to see how the evolutionary trick worked. While observing the reptiles, the team saw that the anoles would inflate the bubble when they exhaled before drawing it back through their nose. The lizards could remain underwater for up to 18 minutes while rebreathing through the air sac.
The scientists then used an oxygen sensor to measure the amount of air within the rebreathed bubble and found that the oxygen concentration decreased while the lizard dove underwater, suggesting that the lizards are using up the oxygen through breathing, reports Jason Goodyer for BBC Science Focus. The researchers also noted that the air bubble stuck onto the anole lizard's hydrophobic, or water-repelling, scales.
"We think this is operating like a rebreathing device," says the study's first author Christopher Boccia, a Ph.D. student at Queen's University in Kingston, Ontario, to National Geographic. A rebreathing scuba-diving device recycles exhaled air and allows the diver to breathe the unused oxygen within it.
The bubbles the anole lizards use may act as a "physical gill" that can pull oxygen from the water while accumulated carbon dioxide escapes into the water over the surface of the bubble in a process known as diffusion, per National Geographic.
Through careful observations of various anoles and noting which ones use the bubble breathing technique, the biologists found that the underwater behavior evolved five separate times in five lineages of anole lizards, National Geographic reports. In total, there are over 400 different species of anole, all showing a variety of colors and sizes, known for their abilities to evolve similar features based on the environment they are in. The researchers plan on further looking into how the behavior evolved in the anole lizards.
"Anoles are a remarkable group of lizards, and the number of ways that this taxon has diversified to take advantage of their environments is mind-boggling," says Lindsey Swierk, a biologist at Binghamton University in New York, to BBC Science Focus.