Everyone knows that most mammals breathe through their mouths and noses. Frogs, on the other hand, can breathe through their skin. But what about turtles? How do these hard-shelled critters get oxygen?
You may have heard a strange rumor that turtles can breathe through their butts. But is that true?
Technically, turtles don’t breathe through their buttocks. That’s because turtles don’t really have “butts”; Instead, they have a multipurpose opening known as the cloaca, which is used for sexual reproduction and egg laying, as well as expelling waste. However, they engage in a process called cloacal breathing, which could be interpreted in a less technical sense as “butt breathing.”
During cloacal breathing, turtles pump water through their cloacal openings and into two sac-like organs known as bursae, which behave like aquatic animals lung, Craig Franklin, a wildlife physiologist at the University of Queensland in Australia who has extensively studied cloacal respiration, told Live Science. Oxygen in the water then diffuses via the papillae, small structures lining the walls of the bursae, and into the turtle’s bloodstream.
Related: Why do turtles live so long?
However, cloacal breathing is very inefficient compared to normal aerobic respiration, and all turtles also have the ability to breathe air much more easily using their lungs. As a result, cloacal respiration is only observed in a small number of freshwater species, which rely on this unorthodox method to overcome challenges they face in unique environments where air is difficult to breathe, such as B. fast-flowing rivers or frozen ponds.
The main group of turtles that really master cloacal breathing are river turtles. There are about a dozen river turtles worldwide that can properly use cloacal breathing, about half of which live in rivers in Australia. These include the Mary River Turtle (Elusor macrurus) and the white-throated snapping turtle (Elseya albagula), said Franklin.
However, some species of river turtles are much better at cloaca breathing than others. The undisputed champion is the Fitzroy River Turtle (Rheodytes leukops) from Australia, which can obtain 100% of its energy from cloacal respiration. “This allows them to potentially stay underwater indefinitely,” Franklin said.
But in all other species, cloacal breathing only increases the time they can stay underwater until they have to surface to catch their breath. “For example, instead of diving under water for 15 minutes [while holding their breath]they can stay underwater for several hours,” he said.
The ability to stay underwater for long periods of time is extremely useful for river turtles, as getting to the surface can be hard work. “For a turtle that lives in fast-moving water, going up to the surface to breathe presents a small problem because you could get swept away,” Franklin said. Staying close to the riverbed also makes it easier to avoid predators like crocodiles, he added.
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Avoiding predators is especially important for baby turtles, which can be targeted by birds and large fish. “The greatest predation risk for a hatching turtle is swimming through the water column to the surface,” Franklin said. As a result, juveniles are usually much better at cloacal breathing than adults, allowing them to spend more time near the river bed until they are large enough to venture to the surface more frequently. So it’s possible that other river turtle species are also capable of cloacal breathing as hatchlings, but then lose that ability later in life, Franklin said.
However, cloacal respiration is much less efficient than aerobic respiration because it takes a lot of energy to pump water into the bursa, reducing the net energy gain the turtles receive. “When we breathe air, practically no energy is required” because gases are light and flow freely in and out of our lungs, Franklin said. “But imagine trying to breathe back and forth a viscous liquid.” Water also has about 200 times less oxygen than an equal volume of air, so turtles have to pump more of it to get the same amount of oxygen, he added.
Related: How do animals breathe underwater?
There are other costs of cloacal breathing as well. When oxygen diffuses across the skin the bursa and into the bloodstream, sodium and chloride ions (charged particles) in the papillae, which are vital for their function cells, diffuse into the water in the opposite direction, causing the cells to stop functioning properly. To counteract this, the turtles have developed special pumps that suck the lost ions back into the cells to maintain normal ion levels. This process, known as osmoregulation, requires additional energy, further reducing the net energy gain from cloacal respiration.
Stuck under ice
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There are also about six or seven species of wintering freshwater turtles throughout North America that are capable of a more restricted form of cloacal breathing. These species, like the Blanding turtle (Emydoidea blandingii), spend months under layers of ice covering ponds winter. Some of these turtles have been under the ice for more than 100 days without taking a single breath, Jackie Litzgus, a wildlife ecologist at Ontario’s Laurentian University, told Live Science. Instead, these turtles can also get oxygen through bursae as well as by gurgling water down their throats, known as buccal pumping, Litzgus said.
However, the cloacal respiration of hibernating turtles is much less complex than that of river turtles, Franklin said. Instead of actively pumping water into their bursae like their river-dwelling relatives do, the wintering turtles ingest oxygen, which passively diffuses through the skin in the bursae. This process is more akin to skin respiration—when oxygen diffuses through an animal’s skin, which occurs in amphibians, reptiles, and to a limited extent some mammals people.
The wintering turtles get away with this passive form of cloacal breathing because they have greatly reduced breathing Metabolism- consume less energy and therefore less oxygen. While under the ice, these turtles don’t move much, retaining their bodies temperature near freezing and can switch to anaerobic respiration — a last resort to generate energy without oxygen — when they’re low on oxygen, Litzgus said.
Originally published on Live Science.