Pencil-length lizards that dive into currents to evade their predators survive underwater by breathing through a bubble that forms on their nostrils, researchers say.
Water anoles live around rocks and plants near streams and waterfalls in Central and South America and are preyed upon by birds, snakes and other lizards, making life in the forest an often short affair.
But the ever-present risk of being eaten alive has driven the lizards to develop various escape strategies. When camouflage and scrambling for cover fail, the lizards launch themselves into currents, where they remain submerged until the threat is over.
Scientists knew that water anoles produced bubbles over their nostrils when they dived for cover, but whether the bubbles helped them stay underwater longer — and thus improved their chances of survival — was far from clear.
“We know that they can stay underwater for a very long time,” said Dr. Lindsey Swierk, who studies anoles at Binghamton University in New York. “We didn’t know if there was actually any functional role for this bubble in respiration.”
When water anoles take the plunge, they exhale to produce a bubble that covers their nostrils. But small bubbles naturally form on the lizard’s hydrophobic, or water-repellent, skin and these join the larger bubble, potentially increasing the amount of oxygen available for breathing.
To see if anoles used their bubbles to breathe underwater, Swierk recorded how long the lizards stayed underwater with and without moisturizer applied to their skin. The moisturizer prevented the bubbles from forming properly.
Write in Biology LettersSwierk describes how water anoles stayed underwater 32% longer without the humidifier to disrupt their bubbles. “When they’re prevented from forming regular rebreathing bubbles, they can’t dive as long,” Swierk said. While the anoles were only submerged for a few minutes in the study, they can be submerged for about 20 minutes in the wild.
Water anoles are so badly predated that Swierk calls them “the chicken nuggets of the forest”. Their first line of defense when spotting a predator is to freeze and hope their camouflage hides them. If the predator is chasing them, the next option is to make a dash for a crack in a rock. Diving into currents is a last resort, not least because it can lower their body temperature and make them sluggish.
“At least for their human pursuers, like our researchers, diving is by far the most efficient way to escape,” Swierk said. “Once they are underwater, they are very difficult to detect through the moving current surface.”
