How alligators 'rock and roll' without creating ripples in water

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Washington, March 14 : Alligators use their lungs like an internal floatation device to manoeuvre without generating a ripple in the water, say researchers.

University of Utah biologists have discovered that alligators shift their lungs towards the tail when they dive, towards their head when they surface, and sideways when they roll. The reptile uses its diaphragm, pelvic, abdominal and rib muscles for shifting its lungs like internal floatation devices, according to the researchers.

"The secret to their aquatic agility lies in the use of several muscles, such as the diaphragmatic muscle, to shift the position of their lungs. The gases in the lungs buoy up the animal, but if shifted forward and backward cause the animal to pivot in a seesaw motion. When the animals displace gases to the right or left side of the body, they roll," says T.J. Uriona, a doctoral student in biology at the university

"It allows them to navigate a watery environment without creating a lot of disturbance. This is probably really important while they are trying to sneak up on an animal but don't want to create ripples," Uriona adds.

C. G. Farmer, an assistant professor of biology, says that the discovery in American alligators suggests "special muscles that manipulate the position of the lungs - and thus the centre of buoyancy - may be an underappreciated but important means for other aquatic animals to manoeuvre in water without actively swimming."

She counts crocodiles, African clawed frogs, some salamanders, turtles and manatees in such animals.

According to her, the use of muscles to move the lungs may be "incredibly important or you would not see it evolve repeatedly."

The study involved five 2-year-old American alligators (Alligator mississippiensis), only 15 inches to 20 inches long as compared to adults that can reach 15 feet.

Electrodes were implanted on five sets of muscles so their activity could be monitored while the alligators maneuvered in 100-gallon fish tanks. While one set of muscles played no role in moving the lungs to help the gators dive and manoeuvre, four did.

The researchers observed that the four muscle types work together to help an alligator shift its lungs so it could rock downward to dive or roll side-to-side. The tail also helps gators roll, they found.

"The muscles are on when they are diving, and the muscles shut off when they start returning to the surface," Uriona says.

Uriona and Farmer's study has been published in the online edition of The Journal of Experimental Biology.

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