Long-clawed shrews grow bigger snouts in winter — SkimNews
SkimNews Take
Winter shrews aren't shrinking uniformly—selective snout enlargement reveals tissue is being redistributed toward thermoregulation rather than simply lost across the body.
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- Dr. Yugo Ikeda of Toyo University and colleagues documented seasonal skull changes in long-clawed shrews, finding the rostrum (snout) expands in winter while the brain case shrinks — a pattern they termed "reverse Dehnel's phenomenon."
- The study examined 136 long-clawed shrew skulls collected in Hokkaido between 1948 and 1988 and now housed at Hokkaido University's Botanical Garden, with findings published in Proceedings of the Royal Society B.
- Brain case height in winter-collected shrews (January–April) was 12% smaller than in younger shrews collected August–September, while snout height was 7% larger and snout width 6% greater.
- The researchers described the snout expansion as a "true change" in which the bone structure of the rostrum physically alters size, with measurements reverting the following August–November in shrews that survived winter.
- Ikeda proposed the expanded nasal cavity warms freezing inhaled air via a rich vascular network before it reaches the shrunken winter brain, and noted the change may also boost the shrew's ability to sniff out prey such as earthworms.
- A third hypothesis — that the larger snout mechanically reinforces foraging on tougher prey during food-scarce months — found little supporting evidence in the data.
- Hokkaido is home to three additional shrew species that Ikeda said the team plans to investigate for the presence or absence of both Dehnel's and reverse Dehnel's phenomena.
Why it matters: The finding shows that winter skull shrinkage in shrews is not uniform across the skull — the snout physically expands while brain case shrinks, a pattern Ikeda's team termed "reverse Dehnel's phenomenon." It also identifies a thermoregulatory role: expanded nasal cavities warm freezing inhaled air before it reaches the shrunken winter brain.
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