February 6, 2013
Stereo Sniffing Helps Common Moles Detect Their Food
[Watch Video: Testing Stereo Sniffing Moles]
Alan McStravick for redOrbit.com - Your Universe Online
Almost all mammals, including us humans, can see and hear in stereo. But which other of our senses might utilize a 3D approach for more effective operation? It turns out a new study, published yesterday in the journal Nature Communications, has found that certain animals are able to smell in stereo, as well.
One of those mammals, the common mole (Scalopus aquaticus), frequently found in the eastern United States, Canada and Mexico, has been found to rely upon stereo sniffing to locate its prey. The study, “Stereo and Serial Sniffing Guide Navigation to an Odor Source in Mammals”, was conducted by Kenneth Catania, the Stevenson Professor of Biological Sciences at Vanderbilt University, who has been thinking on the subject for some time.
In fact, his interest in the mole and its use of its sense of smell goes back a full decade to another study Catania was conducting on the cousin to the common mole, the star-nosed mole and its ability to use its hyper-sensitive sense of touch of its multiple tentacles that encircle its nose.
In Catania´s sense of touch study, the common mole was used 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.”
His initial hypothesis was supported when he undertook a serious examination of the common moles´ sense of smell last year. What Catania discovered, however, was that their use of this stereo smell was even more amazing than he had previously thought.
"I came at this as a skeptic. I thought the moles' nostrils were too close together to effectively detect odor gradients," he said in a statement.
Catania, with the release of his study results, has thrown open the doors to 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,” Catania maintained.
One of the methods created by Catania to test his hypothesis involved the construction of a radial arena that had food wells that were evenly spaced around a 180-degree semi-circle. The entrance for the mole was located in the center of the back wall. With this contraption, Catania was able to perform trials on the moles, randomly placing pieces of earthworm into the food wells. Prior to introducing the mole to the environment, the chamber was temporarily sealed. This allowed Catania to measure even the most minute of air pressure changes brought about by the sniffing of the mole.
"It was amazing. They found the food in less than five seconds and went directly to the right food well almost every time," Catania said. "They have a hyper-sensitive sense of smell."
In addition to recognizing the common moles heightened sense of smell, after several dozen individual trials Catania began to see a general pattern emerge. Upon introduction to the chamber, the mole would move its nose back-and-forth while sniffing. After only a few seconds, the mole was able to zero in on the food and would move quickly towards it. It was this action on the part of the mole that made Catania reconsider his initial dismissal of the notion of stereo sniffing.
Previous studies showed how stationary rats might be trained to detect flowing air through stereo sniffing, but there had never been any study that showed how this trait might actually work as a natural behavior.
As Catania had decided to investigate the concept of stereo smell, he enacted another model to test his theory.
Catania, using a small plastic tube, blocked nostrils, one at a time, on each of the moles. He found when the left nostril was blocked, the moles would veer to the right. Conversely, when the right nostril was blocked, the moles would veer to the left. The implementation of the tube did not prohibit the moles from actually finding the food, but it did take them considerably longer to do so.
A second chamber model was designed. In this second chamber, the food was placed in the same position, directly across from the entrance, each time. Moles that had neither nostril blocked went almost directly to the food every time. However, it was again found that those with their left nostril blocked veered to the right of the food and those with their right nostril blocked veered to the left.
Catania concedes his research methods and findings mirror a 33 year old study.
"This is strikingly similar to a landmark study of hearing in barn owls performed in 1979 by Eric Knudsen and Mark Konishi at [Caltech], who found that blocking one of the owl's ears caused them to misjudge the location of a sound source," he said.
It wasn´t until a third test that the definitive evidence was uncovered showing the moles, in fact, did rely upon stereo sniffing to burrow and find prey. In this test, Catania inserted small tubing into both nostrils of the mole and then crossed them. By crossing the tubes, Catania was able to ensure the right nostril was sniffing air on the left side of the mole and vice versa. It was when the nostrils had been crossed that confusion was allowed to reign. The moles would search back-and-forth for the food and very often would be completely unable to find it.
Upinder Bhalla, a neuroscientist at the National Center for Biological Sciences (NCBS) in Bangalore, India, who has conducted his own research in the field of stereo smell, claims this trait can be very useful for animals that are called upon to make rapid decisions.
“If you can locate the direction of a cat in one sniff rather than two, you would be more likely to survive,”Bhalla told Ker Than of National Geographic News.
While some research has been conducted on stereo smell in humans, Catania still carries his healthy skepticism in this matter.
“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,”he explained.
It is studies such as these that lead Catania to believe only when an odor is strong enough to irritate the nostril lining can humans discern which side is being stimulated.