Tiny-eared and blind, common moles search for tasty meals – like crushed-up earthworms – with their noses. Now a study suggests that these unconventionally adorable critters find their food by smelling in stereo, by detecting small differences in the strength of an odor between the two nostrils.
The study “shows quite directly that stereo olfaction helps with finding food,” said Upinder Bhalla, a neurobiologist at Bangalore’s National Centre for Biological Sciences. Bhalla has studied stereo smelling in rats, but was not a part of the mole team. “It shows how there is a greater reliance on the stereo cues as the animal gets closer to the odor source.”
Stereo sensing is not an unfamiliar capability among mammals. Vision and hearing both work this way, with input from two eyes producing depth perception, and separated ears localizing sound. But for years, the question of whether mammals could smell in stereo has generated controversy. Studies have suggested that both rats and humans could do this, but not everyone believes it.
The new report, published today in Nature Communications, aims to add the common mole (Scalopus aquaticus) to the roster of stereo-sniffers. To test these subterranean furballs, Kenneth Catania, a neurobiologist at Vanderbilt University, constructed a chamber containing 15 food wells arrayed in a semicircle.
Moles placed in the chamber had to follow their noses to a chunk of earthworm randomly hidden in one of the 15 wells. Most sniffed a few times and went directly to retrieve their yummy treasure.
But when one nostril was plugged, a different pattern emerged. Temporarily blocking the left nostril with plastic tubing sent moles veering off to the right. When the right nostril was plugged, the moles favored initial forays to the left. When Catania inserted tubes that crossed the odor cues between left and right, the moles were completely flummoxed. They often wandered around, even missing the wriggling worm completely. A different testing chamber — designed to simulate an underground tunnel — produced similar results.
Catania acknowledges that the findings are unexpected given the tiny distance between a mole’s nostrils. Even so, he argues that the creatures smell in stereo.
Bhalla concurs. “The methods are very sound and you just have to watch the behavior of the mole in the attached movies to see how the stereo olfaction works, and how switching the direction of sampling — using the little tubes in the nostrils — confuses the mole,” he said.
Video: Kenneth Catania
Blind, Fuzzy Moles Smell in Stereo
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Blind, Fuzzy Moles Smell in Stereo
