A bubble of air lets some lizards breathe underwater – Science News for Students

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The bubble of air around its snout lets this lizard in Costa Rica breathe underwater. One champion lizard was able to stay underwater for 18 minutes!
Lindsey Swierk
July 14, 2021 at 6:30 am
Some small lizards have a newfound superpower. They can rebreathe exhaled air underwater. They do it by trapping the air in a bubble on their snouts, a new study shows.
“As anyone who has encountered one of these lizards can tell you, they dive underwater when they feel threatened. They can stay down for a while too — up to 18 minutes by my count,” says Chris Boccia. But how they stayed underwater for so long was a mystery. Until now.
Boccia is a PhD student at Canada’s Queens University in Kingston, Ontario. But five years ago, he was a master’s student in evolutionary biology at the University of Toronto in Canada. Back then, his professor, Luke Mahler, told him a story.
Mahler had been studying an endangered species of Anolis lizard on the Caribbean nation of Haiti in 2009. After releasing a lizard back into a clear, shallow stream, he noticed something odd. The lizard exhaled an air bubble around its snout as the animal clung to the rocky bottom. Then it appeared to repeatedly suck the air in and out of that bubble.
Mahler had to move on to his next research site so he couldn’t explore more. But years later, he still remembered the bubble-headed lizard. Boccia decided to investigate its behavior.
In search of bubble-breathing lizards, Boccia traveled to Costa Rica in 2017. He and his team went out at night to capture the lizards. “Doing this when they’re sleeping makes things less stressful for them,” he explains. It’s also “easier for us to catch them,” he adds. Wearing headlamps to find the lizards in the dark, the team collected 120 lizards near streams and 180 away from streams. The included a range of related species.
The creatures grow to about 11 centimeters (4.5 inches) not counting their tails. Boccia’s group brought the lizards back to their camp, where they set up containers of river water. Then they dunked each lizard underwater. They held each loosely so the critter could surface when it wanted to.
While underwater, all of these lizards carried a bubble of air around their snouts. They appeared to breathe the bubble in and out. Some land-based lizards inhaled the bubble a few times but did not rebreathe a lot. Their river-based relatives re-breathed more often and stayed submerged longer. “One lizard was underwater for 18 minutes,” Boccia recalls. “We were starting to get worried about him.”
The lizards’ water-repelling skin may play a role. As the reptile dives into the water, a thin layer of air may get trapped against that skin. When the lizard now exhales, Boccia thinks that this air exits through the nostrils and expands the trapped air layer. In that way, the lizard might use it lungs to control the bubble’s size.
But if a lizard re-breathed the air in those bubbles, their oxygen levels should drop lower and lower. To test this, Boccia brought a small oxygen sensor and inserted the thin wire-like device into the bubble around the submerged lizards’ snouts.
“It took a lot of practice to do it without bothering them,” he says. But that work confirmed his hunch. The bubbles’ oxygen level slowly dropped as the lizards breathed.
Boccia also noticed that diving lizards closed their eyes, as if sleeping. He now suspects the lizards are slowing down the chemical activities that support cells and organs. That should reduce their need for oxygen so that they could stay down longer.
The new study highlights how different animals have evolved to live in water, says  Jonathan Losos. He’s an evolutionary biologist at Washington University in St. Louis, Mo. Losos studies how lizards adapt to their environments. “Species that experience the same challenge in nature often find different ways to overcome it,” he notes.
“Fish use gills to extract oxygen from the water,” Losos points out. “Whales are able to hold their breath for a long time. And now we know that these lizards take oxygen underwater with them.”
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Boccia has a few ideas that might explain why lizards breathe with bubbles, instead of holding their breath.
The bubble may help them shed carbon dioxide, or CO2. Animals — including us — don’t breathe just to take in oxygen. They also need to exhale CO2. If CO2 built up in their bodies, it could poison them.
CO2 exhaled into the bubbles may escape into the water, Boccia thinks. A bubble may also help the lizards pick up extra oxygen from the water. Oxygen can move between water and air. As oxygen levels drop in the bubble, dissolved oxygen in the stream may enter it to re-balance the levels. This equalizing movement is called diffusion.
Both Boccia and Mahler hope to continue studying this behavior.
“There are so many different types of lizards, there is a good chance that others do it too. We just haven’t seen it,” says Boccia. He published his findings May 12 in the journal Current Biology.
behavior: The way something, often a person or other organism, acts towards others, or conducts itself.
biology: The study of living things. The scientists who study them are known as biologists.
carbon dioxide: (or CO2) A colorless, odorless gas produced by all animals when the oxygen they inhale reacts with the carbon-rich foods that they’ve eaten. Carbon dioxide also is released when organic matter burns (including fossil fuels like oil or gas). Carbon dioxide acts as a greenhouse gas, trapping heat in Earth’s atmosphere. Plants convert carbon dioxide into oxygen during photosynthesis, the process they use to make their own food.
cell: The smallest structural and functional unit of an organism. Typically too small to see with the unaided eye, it consists of a watery fluid surrounded by a membrane or wall. Depending on their size, animals are made of anywhere from thousands to trillions of cells. Most organisms, such as yeasts, molds, bacteria and some algae, are composed of only one cell. (in telecommunications) A technology that relies on a large number of base stations to relay signals. Each base station covers only a small area, which is known as a cell. Phones that rely on this system are typically referred to as cell phones.
chemical: A substance formed from two or more atoms that unite (bond) in a fixed proportion and structure. For example, water is a chemical made when two hydrogen atoms bond to one oxygen atom. Its chemical formula is H2O. Chemical also can be an adjective to describe properties of materials that are the result of various reactions between different compounds.
Costa Rica: A Central American nation with coastlines along both the Pacific Ocean and Caribbean Sea. This country of nearly 5 million people is sandwiched between Nicaragua to the north and Panama to its south. Almost one-fourth of its land consists of protected rainforests, which are home to such animals as spider monkeys and the quetzal birds.
diffusion: (v. to diffuse) The process of spreading out thinly over a great area. It can involve the release or movement of light or some substance through a liquid (such as water or air) or through some surface (such as a membrane).
endangered: An adjective used to describe species at risk of going extinct.
environment: The sum of all of the things that exist around some organism or the process and the condition those things create. Environment may refer to the weather and ecosystem in which some animal lives, or, perhaps, the temperature and humidity (or even the placement of things in the vicinity of an item of interest).
evolutionary biologist: Someone who studies the adaptive processes that have led to the diversity of life on Earth. These scientists can study many different subjects, including the microbiology and genetics of living organisms, how species change to adapt, and the fossil record (to assess how various ancient species are related to each other and to modern-day relatives).
extract: (v.) To separate one chemical (or component of something) from a complex mix. (noun) A substance, often in concentrated form, that has been removed from its natural source. Extracts are often taken from plants (such as spearmint or lavender), flowers and buds (such as roses and cloves), fruit (such as lemons and oranges) or seeds and nuts (such as almonds and pistachios). Such extracts, sometimes used in cooking, often have very strong scents or flavors.
gills: The respiratory organ of most aquatic animals that filters oxygen out of water. Fish and other water-dwelling animals use gills to breathe.
lizard: A type of reptile that typically walks on four legs, has a scaly body and a long tapering tail. Unlike most reptiles, lizards also typically have movable eyelids. Examples of lizards include the tuatara, chameleons, Komodo dragon, and Gila monster.
organ: (in biology) Various parts of an organism that perform one or more particular functions. For instance, an ovary is an organ that makes eggs, the brain is an organ that makes sense of nerve signals and a plant’s roots are organs that take in nutrients and moisture.
predator: (adjective: predatory) A creature that preys on other animals for most or all of its food.
reptile: Cold-blooded vertebrate animals, whose skin is covered with scales or horny plates. Snakes, turtles, lizards and alligators are all reptiles.
sensor: A device that picks up information on physical or chemical conditions — such as temperature, barometric pressure, salinity, humidity, pH, light intensity or radiation — and stores or broadcasts that information.
species: A group of similar organisms capable of producing offspring that can survive and reproduce.
theory: (in science) A description of some aspect of the natural world based on extensive observations, tests and reason. A theory can also be a way of organizing a broad body of knowledge that applies in a broad range of circumstances to explain what will happen. Unlike the common definition of theory, a theory in science is not just a hunch. Ideas or conclusions that are based on a theory — and not yet on firm data or observations — are referred to as theoretical. Scientists who use mathematics and/or existing data to project what might happen in new situations are known as theorists.
threatened: (in conservation biology) A designation given to species that are at high risk of going extinct. These species are not as imperiled however, as those considered “endangered.”
Journal:​ ​​C.K. Boccia et al. Repeated evolution of underwater rebreathing in diving Anolis lizards. Current Biology. Published online May 12, 2021. doi: 10.1016/j.cub.2021.04.040.
Sharon Oosthoek is a freelance science journalist. She likes to write about animals and their habitats. Sharon also really likes chocolate. Her sons have learned to hide their Halloween candy.
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