Winter Nose Growth in Shrews Reveals Surprising Adaptational Strategy

Yugo Ikeda, a mammalogist at Toyo University in Tokyo, and his international collaborators are redefining winter survival strategies through their study of the long-clawed shrew (Sorex unguiculatus). While studying shrews collected from Hokkaido’s extreme environment, an unexpected discovery was made when researchers compared 136 museum skull measurements with seasonal data.

Known for Dehnel’s phenomenon—the winter shrinkage of skulls and brains as an energy-saving adaptation—these shrews defied expectations. Where researchers anticipated reduced nasal cavities, they found the opposite: winter specimens showed 7% increases in snout height (2.43mm) and 6% width expansion (2.19mm), both reverting to baseline in spring. This “reverse Dehnel’s phenomenon” challenges existing paradigms of skeletal plasticity.

Lead author Ikeda calls the finding “completely unexpected and caught us all off guard in the best possible way.” The enlarged nasal cavity likely offers dual benefits: complex blood vessel networks pre-warm inhaled air before reaching the seasonally shrunken brain, while increased surface area improves olfactory detection in deep snow—critical during resource-scarce winters.

Dr. Jan Taylor, independent researcher from Poland, suggests further studies comparing this trait across the shrew’s broader range could elucidate climate-related drivers. Future research will examine tissue-level nasal changes in wild populations—the next frontier for understanding this evolutionary marvel.

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