Long-clawed shrews on the Japanese island of Hokkaido grow larger noses during winter while their brains shrink, according to a study reported in Science News.
The discovery shows that the animals' noses expand in cold weather regardless of other seasonal changes in their bodies, defying the usual pattern of winter tissue reduction in small mammals.
While the seasonal shrinkage of shrews' brains and skulls is a recognized biological process known as Dehnel's phenomenon, researchers found that their snout dimensions move in the opposite direction. During cold months, their noses increase in size by 7 percent vertically and 6 percent horizontally, reaching measurements of up to 2.43 millimetres and 2.19 millimetres respectively.
Reverse Dehnel phenomenon
A research team from Toyo University, led by Yugo Ikeda, uncovered the physical shift after measuring 136 skulls from museum specimens collected across Hokkaido, Japan's northernmost main island. Ikeda called the unexpected expansion a reverse Dehnel phenomenon, noting that it did not align with traditional patterns of winter body tissue reduction.
Dehnel's phenomenon was first documented in small mammals that temporarily reduce their skull, brain, and organ mass to conserve precious energy during freezing months when food is scarce.
Survival in harsh winters
Scientists believe the growing snout plays a crucial role in helping the long-clawed shrew survive severe winter conditions. An enlarged nasal cavity provides extra space for a dense network of blood vessels, which warm cold inhaled air before it reaches the animal's winter-shrunk brain.
The increased snout size also expands the surface area of olfactory tissue inside the nose. This enhanced sense of smell allows the shrews to locate food beneath deep snow cover when environmental resources are limited.
Triggers and future research
Jan R. E. Taylor, an evolutionary ecologist at the University of Bialystok in Poland, said researchers must now investigate whether long-clawed shrews living in milder climates experience the same nasal expansion. Determining whether shrews in warmer regions undergo similar changes will help scientists pinpoint the exact environmental factors that trigger the adaptation.
The study highlights how specialized animal species adapt to extreme environments, following other recent discoveries in animal behavior. In a separate study from the University of California, Berkeley, Dr Julie Elie spent over a decade recording and categorizing zebra finch vocalizations to decode their songs, earning a 100,000 dollar prize, equivalent to about eight million rubles, for her work.
