Turtles Breathe Via Their Anus: An Evolutionary Wonder

Turtles are ectotherms, meaning their body temperature is determined by their environment. As the temperature drops, their metabolism slows down, reducing their energy and oxygen requirements. While hibernating, turtles can obtain oxygen from the water by moving it over their bodies, which are flush with blood vessels. Notably, their cloaca, or butt, has a high density of blood vessels, allowing them to engage in a process called cloacal respiration, which can be likened to breathing through their butts.

The process is called cloacal respiration

The process by which turtles can breathe through their anus is called cloacal respiration. It is important to note that turtles do not have "butts" per se. Instead, they have a multipurpose opening called a cloaca, which is used for reproduction, egg-laying, and expelling waste.

During cloacal respiration, turtles pump water through their cloacal openings and into two sac-like organs called cloacal bursae, which act as aquatic lungs. The cloaca has a high density of blood vessels, making it an efficient site for gas exchange. The oxygen in the water diffuses across the papillae, small structures that line the walls of the bursae, and into the turtle's bloodstream, while carbon dioxide diffuses from the blood out into the water.

Cloacal respiration is not as efficient as normal aerobic respiration, and all turtles can breathe air with their lungs much more easily. Therefore, cloacal respiration is only observed in a small number of freshwater species that have adapted to challenging environments where breathing air is difficult, such as fast-flowing rivers or frozen ponds. The main turtle group that has mastered cloacal respiration is river turtles, with around a dozen species found globally, half of which are native to Australia.

The undisputed champion of cloacal respiration is the Fitzroy River turtle from Australia, which can derive 100% of its energy through this method, allowing it to remain underwater indefinitely. Other river turtle species also benefit from cloacal respiration, as it extends the time they can stay underwater before needing to resurface for air. For example, instead of holding their breath for 15 minutes, they can remain submerged for several hours.

Cloacal respiration is particularly advantageous for river turtles because breaking the surface of the water can be challenging and dangerous. In fast-flowing rivers, turtles risk getting swept away, and in ponds, surfacing can make them more vulnerable to predators such as crocodiles. Additionally, cloacal respiration helps juvenile turtles avoid predators. Baby turtles are a target for birds and large fish, and by staying closer to the riverbed, they can reduce the risk of predation.

It's not true breathing, but diffusion of oxygen and carbon dioxide

Turtles do not breathe through their "butts" in the traditional sense. Instead, they have a multipurpose opening called a cloaca, which is used for reproduction, egg-laying, and expelling waste. However, they do engage in a process called cloacal respiration, which can be likened to "butt breathing".

Cloacal respiration is not true breathing, but rather the diffusion of oxygen and carbon dioxide. During this process, turtles pump water through their cloacal openings and into two sac-like organs called bursae, which function similarly to gills in fish. The oxygen in the water diffuses across the papillae, small structures lining the walls of the bursae, and into the turtle's bloodstream, while carbon dioxide diffuses from the blood into the water. This process is less efficient than normal aerobic respiration, as it requires a lot of energy to pump water into the bursae, and the net gain of energy is reduced due to the additional energy needed for osmoregulation to counteract the loss of vital ions.

Cloacal respiration is observed in a small number of freshwater turtle species, particularly river turtles, and is most effective in species that spend a lot of time in the water, such as the Fitzroy River turtle from Australia, which can derive 100% of its energy through this method. This ability allows them to remain underwater indefinitely and avoid predators.

While it is not true breathing, cloacal respiration is a fascinating adaptation that enables turtles to survive in challenging environments, such as frozen ponds or fast-flowing rivers, where accessing the surface to breathe is difficult or dangerous.

Turtles have a multipurpose opening called a cloaca

During cloacal respiration, turtles pump water through their cloaca and into two sac-like organs called cloacal bursae, which function like gills or aquatic lungs. The cloaca and cloacal bursae have a lot of blood vessels, so they are ideal for absorbing oxygen. The oxygen in the water diffuses across the papillae (small structures that line the walls of the bursae) and into the turtle's bloodstream. This process also allows the turtle to expel carbon dioxide.

Cloacal respiration is not as efficient as breathing air, as it requires a lot of energy to pump the water and the water has much less oxygen than an equal volume of air. However, it is very useful for turtles that live in unique environments, such as fast-flowing rivers or frozen ponds, where it is hard to reach the surface to breathe. It is seen in a small number of freshwater species, particularly river turtles.

The main turtle group that has mastered cloacal respiration is river turtles. Around a dozen river turtle species can properly utilise cloacal respiration, and about half of these live in rivers in Australia. The undisputed champion is the Fitzroy River turtle, which can derive 100% of its energy through cloacal respiration, allowing it to remain underwater indefinitely.

Cloacal respiration is also used by some hibernating turtles, which have a very low metabolism and therefore require very little oxygen. They can survive on the oxygen they absorb through their skin and the cloacal bursae, as well as through buccal pumping, which involves gargling water in their throats.

This process is similar to cutaneous respiration in amphibians and reptiles

Cutaneous respiration, also known as cutaneous gas exchange or skin breathing, is a form of respiration in which gas exchange occurs across the skin or outer integument of an organism rather than through gills or lungs. This process is similar to the cloacal respiration exhibited by turtles, wherein turtles exchange oxygen and carbon dioxide through their cloaca, or butt.

Cutaneous respiration can be the sole method of gas exchange or may accompany other forms of respiration, such as ventilation. It occurs in a wide variety of organisms, including insects, amphibians, fish, sea snakes, turtles, and, to a lesser extent, mammals. The skin serves as both a barrier and a conduit between the external environment and the internal milieu of the animal. It offers a large surface area for potential exchange with the external environment and is constantly in contact with the respiratory medium, whether that be water or air.

In amphibians, the skin is a major site of respiration and plays an important role in gas exchange. For example, the lungless salamander family Plethodontidae lack lungs entirely and rely solely on cutaneous respiration. Similarly, in frogs and other amphibians, cutaneous respiration may be the primary respiratory mode during colder temperatures. In some amphibians, extensive folds of skin increase the rate of respiration, such as in the hellbender salamander and the Lake Titicaca water frog.

While being covered in scales largely precludes cutaneous respiration in reptiles, gas exchange may still occur between the scales or in areas with reduced scales. Some turtles rely on cutaneous respiration from enteral respiration around the cloaca during underwater hibernation. In sea snakes, cutaneous respiration can account for up to 30% of total oxygen uptake and is important when diving.

In summary, cutaneous respiration is a process similar to cloacal respiration in turtles, as it involves the exchange of gases across the skin or outer integument of an organism. This process is observed in a variety of organisms, including amphibians and reptiles, and can be the sole method of gas exchange or complement other forms of respiration.

Only a small number of freshwater species can do this

While it is true that turtles can engage in a process known as cloacal respiration, it is important to clarify that this is not the same as breathing through their anus or butt. This is because turtles do not have a distinct anus or butt; instead, they have a multipurpose opening called a cloaca, which is used for reproduction, egg-laying, and expelling waste.

Cloacal respiration is a process where turtles pump water through their cloacal openings and into two sac-like organs called bursae, which function similarly to gills in fish. The oxygen in the water diffuses across the papillae, small structures lining the walls of the bursae, and into the turtle's bloodstream.

However, it is important to note that cloacal respiration is only found in a small number of freshwater turtle species. These species have evolved this unorthodox method to survive in unique environments where breathing air is challenging, such as fast-flowing rivers or frozen ponds. The main group that has mastered cloacal respiration is river turtles, with around a dozen species globally, half of which are found in Australia.

While cloacal respiration allows these turtles to stay underwater for extended periods, it is much less efficient than normal aerobic respiration. It requires a lot of energy to pump water into the bursae, and the water contains significantly less oxygen compared to air. Therefore, cloacal respiration is not a common ability among freshwater turtles, and they typically rely on their lungs to breathe air.

Frequently asked questions