The results of the research by Vanderbilt's Kenneth Catania, assistant professor of biology, were reported Dec. 21 in the science journal Nature. He became curious when he observed that a mole he was studying blew a lot of bubbles while swimming.
"This came as a total surprise because the common wisdom is that mammals can't smell underwater,' said Catania, who earlier this year won a $500,000 "genius grant" from the John D. and Catherine T. MacArthur Foundation.
"When mammals adapt to living in water, their sense of smell usually degenerates. The primary example is the cetaceans ?whales and dolphins ?many of which have lost their sense of smell."
Catania devised a series of experiments to determine whether the star-nosed mole and another small, semi-aquatic mammal - the water shrew - can smell objects underwater. Using a high-speed camera, he discovered how they do it. After observing that the moles were blowing bubbles out of their nostrils and then sucking them right back in, he determined they were exhaling and inhaling the bubbles rapidly, between five and 10 times per second. That is about the same rate as the sniffing behavior of comparably sized land mammals, like rats and mice. "Rats and mice don't sniff the way we do," Catania said. "They push air 'out-in out-in' in a fashion strikingly similar to what the star-nosed mole is doing, except that it is doing it under water."
Catania mounted a high-speed video camera so that it pointed up through the bottom of a glass tank. Then he stuck various objects on the bottom of the tank ?pieces of earthworm, small fish, insect cuticle and blobs of wax and silicon ?and observed the moles' behavior. He saw that, when the moles approached one of these targets, they would blow bubbles that came into contact with the t