Long-clawed shrews grow bigger winter snouts, study finds
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- Long-clawed shrews examined via 136 skulls collected in Hokkaido between 1948 and 1988 (now housed at Hokkaido University's Botanical Garden) showed winter snouts 7% taller and 6% wider than younger shrews, while brain case height shrank 12%.
- Toyo University researcher Dr. Yugo Ikeda led the study, published in Proceedings of the Royal Society B, terming the finding "reverse Dehnel's phenomenon."
- The rostrum expansion is a "true change" to bone structure, not soft tissue fluctuation, Ikeda said.
- The seasonal skull changes proved reversible — shrews surviving winter and collected August-November of their second year had larger brain case height again, with snout width — though not height — smaller.
- The team proposed the expanded nasal cavity warms freezing inhaled air via a rich vascular network, protecting the winter-shrunken brain and possibly boosting ability to sniff prey like earthworms.
- A third hypothesis — that the bigger snout mechanically reinforces processing tougher winter prey — found little evidentiary support.
- Hokkaido is home to three other shrew species that Ikeda's team plans to investigate for the same phenomenon.
Why it matters: Documenting reverse Dehnel's phenomenon in long-clawed shrews — where the rostrum physically expands while other skull parts shrink — opens a new line of inquiry into cold adaptation in small mammals, with Ikeda's team now planning to check three other Hokkaido shrew species for the same effect.
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