According to a research published in the journal Nature Communications, the eastern mole (Scalopus aquaticus) relies on stereo sniffing to locate its prey.
The eastern mole Scalopus aquaticus (Kenneth Catania, Vanderbilt University)
Prof Kenneth Catania from Vanderbilt University, who conducted the research, said: “I came at this as a skeptic. I thought the moles’ nostrils were too close together to effectively detect odor gradients.” What he found turned his assumptions upside down and opened new areas for potential future research. “The fact that moles use stereo odor cues to locate food suggests other mammals that rely heavily on their sense of smell, like dogs and pigs might also have this ability.”
Prof Catania’s interest in the common mole’s sense of smell dates back ten years when he was studying the remarkable sense of touch of the common moles’ cousin, the star-nosed mole, which uses a set of fleshy tentacles surrounding its nose to detect edible objects as it burrows. He decided to test the common moles’ capability to find prey for comparison purposes.
“I expected the common mole, which is virtually blind and doesn’t have a very good sense of touch, to be a lot worse than the star-nosed mole. So I was quite surprised when they turned out to be very good at locating prey. At the time, I figured that they must be using their sense of smell, but I didn’t pursue the matter.”
When the neuroscientist began seriously studying the common moles’ sense of smell last year, he discovered that it was even more remarkable than he had expected.
Prof Catania created a radial arena with food wells spaced around a 180-degree circle with the entrance for the mole located at the center. He then ran a number of trials with the food (pieces of earthworm) placed randomly in different wells. The chamber was temporarily sealed so he could detect each time the mole sniffed by the change in air pressure.
“It was amazing. They found the food in less than five seconds and went directly to the right food well almost every time,” Prof Catania said. “They have a hyper-sensitive sense of smell.”
After observing dozens of trials, he noticed a general pattern. When the mole first entered the chamber, it moved its nose back and forth as it sniffed, but then it seemed to zero in on the food source, and moved in a direct path. This was pretty remarkable, and made Prof Catania reconsider the idea of stereo sniffing. Although there is evidence for this ability in stationary rats trained to detect flowing air, no one had shown how this might work for a natural behavior.
The definitive evidence that the moles rely on stereo sniffing came from yet another test. Prof Catania inserted small plastic tubes in both of the moles’ nostrils and crossed them, so the right nostril was sniffing air on the animal’s left and the left nostril was sniffing air on the animal’s right. When their nostrils were crossed in this fashion, the animals searched back and forth and frequently could not find the food at all.
As for humans, Prof Catania remains skeptical. “In humans, this is easier to test because you can ask a blindfolded person to tell you which nostril is being stimulated by odors presented with tubes inserted in the nose.” Such studies suggest it is only when an odor is strong enough to irritate the nostril lining that humans can tell which side is most strongly stimulated.
_______
Bibliographic information: Kenneth C. Catania. 2013. Stereo and serial sniffing guide navigation to an odour source in a mammal. Nature Communications 4, article number: 1441; doi: 10.1038/ncomms2444
