May 20, 2010

Musk Turtles Breathe Underwater Through Their Tongues

One type of turtle possesses an extraordinary organ that lets the reptile breathe underwater and stay submerged for many months.

Scientists have discovered that the common musk turtle has a tiny tongue lined with specialized buds. 

The turtles use their tongues to exchange oxygen, solving a mystery of how these reptiles can remain submerged for so long.

The findings were reported in the journal The Anatomical Record.

"I was very surprised, I really didn't expect that," zoologist Egon Heiss, who is studying for his PhD at the University of Vienna in Austria, told BBC News.

Heiss and colleagues made the discovery while studying the feeding habits of the common musk turtle, which is a freshwater species that inhabits lakes and rivers in southern Canada and the eastern U.S.

Adults spend most of their lives underwater, but juveniles occasionally come onto land in order to find food.

The researchers noticed that when the animals found food, they could only eat it after dragging it back into the water.

Out of land the turtles struggled to swallow their prey.

The turtle has a weak and tiny tongue covered with and surrounded by specialized bud-like cells called papillae.

Further tests showed that the turtle uses these cells around its tongue to breathe.  It draws in oxygen from the water that passes over them.

"We knew that an organ for aquatic respiration must be present somewhere but finally discovered it accidentally," Heiss told BBC News.

Some turtles cannot breathe underwater at all.

For example, all marine turtles must come to the surface at least every few hours for a breath of air.

Some freshwater turtles cannot breathe underwater, while others can do so through their skin.

Other species cope by using specialized cavities in their rear known as cloacal bursae, which draws in water and removes oxygen.

These turtles, which are found in Australia, often need to spend long periods of time underwater, where they hibernate, remaining asleep and still, not feeding and slowing their metabolic rates.

"Musk turtles, however, lack cloacal bursae and their skin is relatively thick and lacks a well developed capillary network," Heiss told the BBC.

It still remains a mystery how these turtles can spend months underwater without coming to the surface, as they cannot take in enough oxygen through their skin.

"We found the large papillae in the throat and were immediately fascinated," Heiss said.

He and his colleagues said the musk turtle's tongue is likely to be an ancient trait.

Turtles are among the longest surviving group of higher land vertebrates.  They are estimated to have existed for 220 million years.

"I truly believe there's still a lot to discover," he continued.

"This study shows how plastic adaptations to certain environmental circumstances can be in turtles."

Image Courtesy Suzanne L. Collins, CNAH


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