Can turtles really breathe through their butts?

Depending on how you define "butts" and "breathe,"

Most animals breathe via their mouths and noses, as is common knowledge. Frogs, on the other hand, have skin-based respiration. What about turtles, though? How can these creatures with hard shells receive oxygen?

There's a curious myth that turtles can breathe via their butts, which you may have heard. But is this actually the case?

In reality, turtles don't actually breathe through their behinds. That's because turtles don't actually have "butts"; instead, they have a cloaca, a multifunctional orifice that serves as a site for sexual reproduction, egg laying, and waste discharge. They do, however, engage in cloacal respiration, which in a less scientific context may be understood as "butt breathing."

According to Craig Franklin, a wildlife physiologist at The University of Queensland in Australia who has extensively studied cloacal respiration, turtles pump water through their cloacal openings and into two sac-like organs known as bursae during this process, which functions somewhat like aquatic lungs. The water's oxygen then permeates the papillae, tiny structures that border the bursae, and enters the turtle's circulation.

Cloacal respiration is substantially less effective than regular aerobic respiration, and all turtles can breathe air via their lungs much more readily. Because of this, cloacal respiration is only observed in a tiny number of freshwater species, which rely on this unconventional strategy to get by in unusual conditions where it is difficult to breathe air, including swiftly flowing rivers or frozen ponds.

Cloacal winners

River turtles are the primary group of turtles that have fully mastered cloacal respiration. The Mary River turtle (Elusor macrurus) and the white-throated snapping turtle (Elseya albagula) are two of the twelve river turtle species worldwide that may effectively employ cloacal respiration, according to Franklin.

However, certain river turtle species are far more adept at cloacal respiration than others. The uncontested winner is the Australian Fitzroy River turtle (Rheodytes leukops), which can obtain all of its energy via cloacal respiration. According to Franklin, "this enables them to potentially stay underwater eternally."

Cloacal respiration, however, just lengthens the time other species may remain underwater before they must surface for air. He explained, "For instance, they can stay underwater for several hours rather than going down for 15 minutes while holding their breath.

For river turtles, the able to stay underwater for lengthy periods of time is quite helpful because rising to the surface may be taxing. Going to the surface to breathe poses a little bit of a problem for a turtle that lives in swiftly moving water because you may get carried away, according to Franklin. He stated that being near the riverbank also makes it simpler to avoid predators like crocodiles.

For young turtles, which are vulnerable to attack from birds and huge fish, avoiding predators is especially crucial. A hatchling turtle's journey to the surface via the water column poses the greatest risk of predation, according to Franklin. Juveniles can spend more time close to the riverbed until they are large enough to begin going more regularly to the surface since they typically do cloacal respiration considerably better than adults. Accordingly, it's plausible that other species of river turtles may similarly breathe through their cloaca as youngsters but lose this capacity as they age, according to Franklin.

Cloacal respiration is far less effective than aerobic respiration, though, because the energy required to pump water into the bursae lowers the turtles' overall energy gain. Franklin stated that since gases are light and easily move in and out of our lungs, breathing air requires "absolutely little energy." But picture attempting to breathe in and out of a thick liquid. According to him, turtles must pump more water to obtain the same amount of oxygen since water has around 200 times less oxygen than an equivalent volume of air.

The expense of cloacal respiration is also another factor. The sodium and chloride ions (charged particles) inside the papillae, which are essential to the functioning of cells, diffuse in the reverse direction into the water when oxygen diffuses past the skin of the bursae and into the circulation, which prevents the cells from working correctly. The turtles have developed specialized pumps that draw the lost ions back into the cells in order to maintain normal ion levels as a defense against this. The net gain in energy from cloacal respiration is further decreased by this extra energy-intensive process, known as osmoregulation.

Under the ice

A smaller kind of cloacal respiration is also possible in perhaps six or seven species of hibernating freshwater turtles in North America. These species, like the Blanding's turtle (Emydoidea blandingii), are trapped in ponds throughout the winter for months by thick sheets of ice. Jackie Litzgus, a wildlife ecologist at Laurentian University in Ontario, told Live Science that some of these turtles can survive under the ice for more than 100 days without being able to breathe air. Instead, these turtles may also absorb oxygen through bursae and a process known as buccal pumping, which involves gargling water in the throat.

Franklin noted that cloacal respiration in hibernating turtles is far less sophisticated than that in river turtles. Unlike their river-dwelling relatives, hibernating turtles take up oxygen that passively diffuses over the skin in the bursae rather than actively pumping water into them. Similar to cutaneous respiration, which occurs in frogs, reptiles, and, to a lesser extent, some mammals, including humans, this mechanism involves the diffusion of oxygen through the skin of the animal.

The reason why the hibernating turtles can get away with this passive cloacal respiration is because they have a far lower metabolic rate, which means they use less oxygen and less energy. These turtles don't move around much under the ice, maintain a body temperature close to freezing, and have the ability to convert to anaerobic respiration, which is a last option for producing energy without oxygen, when they run low, according to Litzgus.