Nav: Home

Soft-shelled turtles urinate through mouth

October 11, 2012

Chinese soft-shelled turtles are exquisitely adapted to their aquatic lifestyle, sitting contentedly on the bottom of brackish muddy swamps or snorkelling at the surface to breath. According to Y. K. Ip from the National University of Singapore, they even immerse their heads in puddles when their swampy homes dry up: which intrigued Ip and his colleagues. Why do these air-breathing turtles submerge their heads when they mainly depend on their lungs to breathe and are unlikely to breathe in water? Given that some fish excrete waste nitrogen as urea - in addition to ammonia - and expel the urea through their gills, the team wondered whether the turtles were plunging their heads into water to excrete waste urea through their mouths, where they have strange gill-like projections. Ip and his colleagues publish their discovery that turtles effectively urinate through the mouth in The Journal of Experimental Biology at http://jeb.biologists.org.

Purchasing turtles from the local China Town wet market and immersing them in water for 6 days, the team measured the amount of urea that passed into the turtles' urine and found that only 6% of the total urea that the animals produced was excreted through the kidneys. Removing the turtles from the water and providing them with a puddle to dip their heads into, the team noticed that the turtles submerged their heads occasionally and could remain underwater for periods lasting up to 100 minutes. They also calculated the excretion rate of urea through the mouth by measuring the amount of urea that accumulated in the water and found that it was as much as 50 times higher than the excretion rate through the cloaca. And when the team injected urea into the turtles and measured their blood- and saliva-urea levels, they realised that the saliva-urea levels were 250 times greater than in the blood. The turtles were dipping their heads into water to excrete urea through their mouths.

Knowing this, the team reasoned that the animals must produce a specialised class of protein transporters in their mouths to expel the waste and, as these transporters can be deactivated by phloretin, the team decided to test the effect of phloretin on the turtle's ability to excrete urea. When the turtles were supplied with phloretin in their puddle of water, they were unable to excrete urea from their mouths when they submerged their head. And when the team analysed the turtles' cDNA, they found that the animals carried a gene that was very similar to urea transporters found in other animals. Finally, they checked to see if the turtles express this gene in their mouths and found evidence of the mRNA that is necessary to produce the essential urea transporter, allowing the reptiles to excrete urea waste through the mouth.

So, why do Chinese soft-shelled turtles go to such great lengths to excrete urea through their mouths when most other creatures do it through their kidneys? Ip and his colleagues suspect that it has something to do with their salty environment. Explaining that animals that excrete urea have to drink a lot, they point out that this is a problem when the only water available is salty - especially for reptiles that cannot excrete the salts. The team says, 'Since the buccopharyngeal [mouth and throat] urea excretion route involves only rinsing the mouth with ambient water, the problems associated with drinking brackish water... can be avoided'.

-end-

IF REPORTING ON THIS STORY, PLEASE MENTION THE JOURNAL OF EXPERIMENTAL BIOLOGY AS THE SOURCE AND, IF REPORTING ONLINE, PLEASE CARRY A LINK TO: http://jeb.biologists.org/content/215/21/3723.abstract

REFERENCE: Ip, Y. K., Loong, A. M., Lee, S. M. L., Ong, J. L. Y., Wong, W.P. and Chew, S. F. (2012). The Chinese soft-shelled turtle, Pelodiscus sinensis, excretes urea mainly through the mouth instead of the kidney. J. Exp. Biol. 215, 3723-3733.

This article is posted on this site to give advance access to other authorised media who may wish to report on this story. Full attribution is required, and if reporting online a link to jeb.biologists.com is also required. The story posted here is COPYRIGHTED. Therefore advance permission is required before any and every reproduction of each article in full. PLEASE CONTACT permissions@biologists.com

THIS ARTICLE IS EMBARGOED UNTIL THURSDAY, 11 October 2012, 00.15 HRS EDT (04:15 HRS GMT, 05:15BST)

The Company of Biologists
Warming temperatures threaten sea turtles
This research suggests that that warmer temperatures associated with climate change may lead to higher numbers of female sea turtles and increased nest failure.
Soft shelled turtles, food in China, likely spread cholera
The pathogen, Vibrio cholerae can colonize the surfaces, as well as the intestines of soft shelled turtles.
Logging threatens breeding turtles
Debris from logging in tropical forests is threatening the survival of hatchling leatherback turtles and the success of mothers at one of the world's most important nesting sites in Colombia.
Is it a boy or is it a girl? New method to ID baby sea turtles' sex
Is it a boy or is it a girl? For baby sea turtles it's not that cut and dry.
Study shows signs of hope for endangered sea turtles
Bones from dead turtles washed up on Mexican beaches indicate that Baja California is critical to the survival of endangered North Pacific loggerhead sea turtles, which travel some 7,500 miles from their nesting sites in Japan to their feeding grounds off the coast of Mexico.
Exeter research helps protect loggerhead turtles
A long-running research and conservation project is helping save an at-risk species of turtle.
Nomads no more, leatherback turtles find permanent coastal home
Endangered leatherback sea turtles are known for their open-ocean migratory nature and nomadic foraging habits - traveling thousands of miles.
Belize's Glover's Reef providing refuge for new generation of sea turtles
A new generation of threatened hawksbill sea turtles is thriving in the protected waters of Glover's Reef Atoll, Belize, evidence that efforts to protect these and other marine species in one of the world's great barrier reef systems are working, according to WCS (Wildlife Conservation Society) and the Belize Fisheries Department.
Too many turtles? Scientists may have solved the mystery of Raine Island
Why do so few turtle eggs hatch on Raine Island, the largest and most important nesting site for green turtles in the world?
Using Lake Michigan turtles to measure wetland pollution
Decades of unregulated industrial waste dumping in areas of the Great Lakes have created a host of environmental and wildlife problems.

Best Science Podcasts 2017

We have hand picked the best science podcasts for 2017. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.

Now Playing: Radiolab

Truth Trolls
Today, a third story of folks relentlessly searching for the truth. But this time, the truth seekers are an unlikely bunch... internet trolls.


Now Playing: TED Radio Hour

Rethinking School
For most of modern history, humans have placed smaller humans in institutions called schools. But what parts of this model still work? And what must change? This hour, TED speakers rethink education.TED speakers include teacher Tyler DeWitt, social entrepreneur Sal Khan, international education expert Andreas Schleicher, and educator Linda Cliatt-Wayman.