Alligators can stealthily maneuver through the water leaving nary a ripple, despite having neither fins nor flippers like other adept swimmers. Instead, they use special muscles to shift the position of their lungs, U.S. researchers said on Thursday.
They said American alligators use their diaphragm, pelvic, abdominal and rib muscles to change their center of buoyancy, forcing the lungs toward the tail when they dive, toward the head when they surface, and sideways to roll.
"What this does is it gives the animal a way to change trajectory," said T.J. Uriona, a doctoral student at the University of Utah, whose study appears in the Journal of Experimental Biology.
"It allows them to quietly change how they are positioned in the water so they can strike," he said in a telephone interview.
"This doesn't require any really quick movements that might give their position away."
Uriona and colleagues think this adept manipulation of special muscles to control buoyancy may be important to other aquatic animals, including African clawed frogs, some salamanders, turtles and manatees.
"It might be more widespread. It's not just unique to crocodilians," Uriona said.
Uriona said the research offers a different theory on why alligators have diaphragm muscles, which are not common among reptiles.
He said the alligator's crocodilian ancestors in the Triassic period — which started 250 million years ago — were cat-sized land dwellers. Many researchers have assumed the diaphragm evolved to facilitate breathing while the animal was running.
To study the function of these muscles, Uriona and Utah biology professor C.G. Farmer studied 2-year-old American alligators from Louisiana's Rockefeller Wildlife Refuge near Grand Chenier.
The gators were just under two feet long, far more manageable than an adult gator, which can reach 15 feet from the tip of the snout to the end of the tail.
They attached electrodes to track the movement of their muscles and a digital device that measured their trajectory in the water. Then they put the animals in an aquarium the size of a small bathtub and watched them dive and roll.
They found the animals could deftly pull their lungs back to lift the tail for diving, shift them to the side to roll, and push them forward to surface.
Uriona likened the process to wearing a life preserver in a swimming pool. Properly worn, the jacket keeps the head afloat.
"But, if you put a life jacket around your middle, that would cause your waist to flip up and your head to sink," he said.
That is basically what the gator is doing when it dives.
