Evolution Diary

Nashville, Tennessee - A United States neurobiologist studying a sensory organ on a little-known semi-aquatic mole has discovered that mammals can smell underwater.

The proboscis that gives the star-nosed mole its name is one of the most sensitive organs of touch in all mammals, says Ken Catania, a professor from Vanderbilt University.

Catania’s discovery appeared in the scientific journal Nature on Thursday.

While filming the mole in slow motion underwater, Catania noticed something weird.

The animal was using its unusual nose not only to touch the objects it encountered, but also to blow air bubbles at them and then suck these bubbles rapidly back in.

“Why on earth would they being doing this, and re-inhaling the bubbles?” he thought. “One obvious conclusion was this is a great way to pick up odours.”

Catania had never thought to question the common scientific assumption that mammals were unable to smell underwater.

“It makes sense from the obvious fact that they would need to inhale air,” he said.

But, as he studied the video on slow motion, the star-nosed mole appeared to be sniffing.

Moles follow trail

Catania devised a simple way to test this: He laid down an underwater scent trail leading to food.

His moles were able to follow the trails with great accuracy, and he was convinced they were using the air bubbles to smell.

Then, to be sure this was not just a fluke, Catania decided to test another semi-aquatic mammal. The water shrew was also able to follow a scent trail.

A star-nosed mole detects scents underwater by blowing and then inhaling bubbles while it forages.

Catania likened the behaviour of the mole and shrew to that of mice and rats, which also exhale and then inhale when sniffing for food.

Watching a video of the mole blowing and inhaling bubbles on his office computer screen, Catania said, “What’s so weird about it is that you usually don’t get to see a sniff, because air in air … you can’t see that. And here we’re basically seeing a sniff.”

Fastest known eater

Charles J Wysocki, a neuroscientist with the Monell Chemical Senses Centre in Philadelphia who was not involved with Catania’s research, called the discovery “incredible”.

“It speaks to the importance that olfaction plays, even in an environment where it was thought to be impossible,” he said. “These critters are making use of smell to find food underwater.”

The study suggests that other semi-aquatic mammals, like seals and otters, could have this ability, something Catania hopes to research in the future.

Catania’s work won him a MacArthur Foundation “genius grant” earlier this year.

It also won a mention in the Guinness Book of World Records after he reported in Nature last year that the star-nosed mole could identify and devour a meal in less than a quarter of a second, making it one of the fastest known eaters in the world.

The ability to smell in water is shared by the water shrew, diving from a log, and being tempted by a crayfish, above.