June 18, 2014
Scientists Solve The Mystery Of Why Some Turtles Use Rear-End Respiration
redOrbit Staff & Wire Reports - Your Universe Online
When it comes to most creatures, the hindquarters tend to be responsible for only one specific task. However, some types of turtles possess rear ends capable of multitasking – and now experts believe they know why.
According to Esther Inglis-Arkell of io9.com, species such as the Australian Fitzroy river turtle and the North American eastern painted turtle can breathe through their back ends, even though both creatures can breathe through their mouths if so desired.
But that’s not all. When scientists placed a tiny bit of food coloring in water located near these turtles, they saw that the reptiles were actually taking in water from both their front and hind ends (and in some cases, just the backside). This is because the rear of a turtle isn’t technically an anus, it’s a different type of opening known as a cloaca.
Inglis-Arkell explained that a cloaca is an opening through which the turtle excretes waste, urinates and lays its eggs. So why, if the turtle can use its mouth to breath, does it sometimes use its anus for this task? Apparently, the answer to this mystery has to do with the turtle’s shell, which evolved when ribs and vertebrae fused together.
“When a turtle hibernates, it buries itself in cold water for up to five months,” the io9.com reporter said. “To survive, it has to change a lot of things about the way its body works. Some processes, such as fat burning, go anaerobic – or without oxygen – in a hibernating turtle.”
These anaerobic processes cause lactic acid to build up, which can cause tremendous damage. The shell is capable of both storing some lactic acid and releasing bicarbonates into the turtle’s body. Without ribs that expand and contract, turtles have no need for the lung and muscle systems typically found in mammals.
In their place, turtles have a unique set of muscles that pull the body towards the openings of the shell, which allow it to inhale, and a second set of muscles that press its guts against its lungs in order to allow the reptile to exhale. This unique set-up requires a lot of work, Inglis-Arkell said, especially since it also results in an increase in lactic acid levels and a decrease in oxygen levels every time that the turtle inhales and exhales.
“Compare this to the relatively cheap butt breathing,” she added. “Sacs next to the cloaca, called bursa, easily expand. The walls of these sacs are lined with blood vessels. Oxygen diffuses through the blood vessels, and the sacs are squeezed out. The entire procedure uses little energy for a turtle that doesn't have a lot to spare.”
Ian Lang of Daily Digest News went on to explain that the phenomenon of “breathing” through their backsides helps some species of turtles, especially those that live in cold habitats where they have to hibernate in order to survive, use the cloaca to breathe in and out in low-oxygen environments.
“The cloaca of some kinds of freshwater turtles, such as our eastern painted turtle, has fingerlike extensions that are abundantly supplied with blood vessels,” added biologist and Northern Woodlands magazine author Bill Amos. “The muscular walls of the cloaca contract and relax forcing water in and out of the chamber.”
“If a painted turtle hibernates in a pond where some dissolved oxygen is available, the cloaca will serve as a respiratory device. As a substitute ‘lung,’ the cloaca allows for the transfer of oxygen and carbon dioxide between animal and the surrounding water,” he added. “Only certain turtles have this ability, but those that do carry on oxygen-fueled metabolism under low-oxygen conditions.”