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 creatures get oxygen?
You may have heard a strange rumor that turtles can breathe through their buttocks. But is it true?
Technically, turtles do not breathe through their bottoms. This is because turtles don’t really have “butts”; instead they have a multi-purpose opening known as the cloaca, which is used for sexual reproduction and egg laying as well as the expulsion of waste products. However, they do engage in a process called cloacal breathing, which could, in a less technical sense, be interpreted as “bottom breathing”.
During cloacal respiration, turtles pump water through their cloacal openings and into two sac-like organs called bursae, which act somewhat like aquatics. lungs, Craig Franklin, a wildlife physiologist at the University of Queensland in Australia who has studied cloacal respiration extensively, told Live Science. The oxygen in the water then diffuses through the papillae, small structures that line the walls of the bursa, and into the turtle’s bloodstream.
Related: Why do turtles live so long?
However, cloacal respiration is very inefficient compared to normal aerobic respiration, and all turtles also have the ability to breathe in air much more easily with their lungs. As a result, cloacal respiration is only observed in a small number of freshwater species that rely on this unorthodox method to overcome the challenges they face in unique environments where it is difficult to breathe from. the air, such as fast-flowing rivers or frozen ponds.
The main group of turtles that have really mastered cloacal breathing are the river turtles. Globally, there are a dozen river turtles that can properly use cloacal respiration, about half of which live in the rivers of Australia; these include the Mary River turtle (Elusor macrurus) and the White-throated Snapping Turtle (Elseya albagula), Franklin said.
However, some species of river turtles are much better at cloacal respiration than others. The undisputed champion is the Fitzroy River Turtle (Rheodytes leukops) from Australia, which can derive 100% of its energy from cloacal respiration. “This allows them to potentially stay underwater indefinitely,” Franklin said.
But for all other species, cloacal breathing only extends the amount of time they can stay underwater until they need to surface to breathe. “For example, instead of diving underwater 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-flowing water, getting to the surface to breathe is a problem because you could get swept away,” Franklin said. Staying close to the riverbed also makes it easier to avoid predators such as 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 normally much better at cloacal respiration than adults, allowing them to spend more time near the riverbed until they are large enough to start venturing more frequently. on the surface. Therefore, it’s possible that other species of river turtles may also be capable of cloacal respiration as juveniles, but then lose that ability later in life, Franklin said.
However, cloacal respiration is much less efficient than aerobic respiration because pumping water into the bursae requires a lot of energy, which reduces the net energy gain turtles receive. “When we breathe air, there is practically no need for energy” because gases are light and flow freely in and out of our lungs, Franklin said. “But imagine trying to breathe a viscous liquid back and forth.” Water also contains about 200 times less oxygen than an equal volume of air, so turtles have to pump in more to get the same amount of oxygen, he added.
Related: How do animals breathe underwater?
There is also another cost to cloacal breathing. When oxygen diffuses through the skin bursae and in the bloodstream, sodium and chloride ions (charged particles) inside the taste buds, which are essential for the functioning of cells, diffuse in the opposite direction in the water, which prevents the cells from functioning properly. To counter this, the turtles have developed special pumps that suck the ions lost into the cells to maintain normal ion levels. This process, known as osmoregulation, requires additional energy, further reducing the net energy gain of cloacal respiration.
Stuck under the ice
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There are also about six or seven species of hibernating freshwater turtles across North America that are capable of a more limited form of cloacal breathing. These species, such as the Blanding’s Turtle (Emydoidea blandingii), spend months trapped under the layers of ice that cover the ponds during the Winter. Some of these turtles have been under the ice for more than 100 days without being able to take a single breath of air, Jackie Litzgus, a wildlife ecologist at Laurentian University in Ontario, told Live Science. Instead, these turtles can also take in oxygen through the bursae, as well as by gargling water down their throats, which is known as mouth-pumping, Litzgus said.
However, the cloacal respiration of hibernating turtles is much less complex than what river turtles are capable of, Franklin said. Instead of actively pumping water into their pouches like their river-dwelling relatives do, hibernating turtles take in oxygen which passively diffuses through the skin into the pouches. This process is more like cutaneous respiration – when oxygen diffuses through an animal’s skin, which occurs in amphibians, reptiles and, to a limited capacity, some mammals, including humans.
Hibernating turtles get away with this passive form of cloacal respiration because they have a metabolic which means they need less energy and therefore less oxygen. When under the ice, these turtles do not move much, keep their bodies Temperature near freezing and can switch to anaerobic respiration — a last resort for creating energy without oxygen — when they run out of oxygen, Litzgus said.
Originally posted on Live Science.