Study of long-clawed shrew skulls from Japan shows that while skulls get smaller in winter, snouts elongate<\/p>\n
Humans turn to heated blankets and fluffy socks to cope with winter, but long-clawed shrews have a very different adaptation: they increase the size of their snouts.<\/p>\n
Researchers have previously discovered that certain small mammals, including the common shrew and European mole, reversibly shrink their body mass, skull size and brain mass in winter, with regrowth seen in the spring \u2013 a strategy that has been named Dehnel\u2019s phenomenon.<\/p>\n
Scientists now say they have documented similar changes in the long-clawed shrew, but have discovered the opposite trend occurs for the snout.<\/p>\n
\u201cThis is precisely why we termed it the \u2018reverse Dehnel\u2019s phenomenon\u2019,\u201d said Dr Yugo Ikeda, first author of the research from Toyo University in Japan.<\/p>\n
Writing in the journal Proceedings of the Royal Society B, Ikeda and colleagues describe how they examined 136 skulls from long-clawed shrews, collected in Hokkaido between 1948 and 1988 and now housed at the Botanical Garden of Hokkaido University in Japan.<\/p>\n
\u201cMeasuring skull structures in live, wild shrews repeatedly without harming them is practically impossible,\u201d said Ikeda.<\/p>\n
The researchers note that wild, long-clawed shrews are born between spring and autumn and typically die before they reach their second winter. The specimens available covered each month of this lifespan, and were classed as belonging to either a sexually immature or sexually mature shrew.<\/p>\n
Tracking 16 measurements by month, they found several changed by month or season \u2013 and not in a uniform way.<\/p>\n
Among other findings, shrews collected over the winter season, between January and April, were found to have a brain case height (vertical skull measurement) 12% smaller than that of younger shrews collected from August to September in their first year of life. However, the height of the snout, also known as the rostrum, was 7% larger and its width was 6% greater in shrews collected in winter.<\/p>\n
\u201cThis is a \u2018true change\u2019 where the bone structure of the rostrum itself physically alters its size,\u201d said Ikeda. \u201cWhat makes this particularly unique is that the rostrum expands while other parts of the skull shrink during winter.\u201d<\/p>\n
The team said these changes were reversible, with measurements including brain case height found to be larger in shrews that survived winter and were collected between August and November in their second year. By contrast, snout width \u2013 although not snout height \u2013 was smaller.<\/p>\n
The researchers suggest a number of explanations for the seasonal change in snout size, including regulating body temperature.<\/p>\n
\u201cExpanding the nasal cavity creates more room for a rich vascular network,\u201d said Ikeda. \u201cWhen the shrew inhales freezing air, this network efficiently warms it before it reaches the delicate, winter-shrunken brain \u2013 helping maintain core cognitive functions.\u201d The expansion of the nasal cavity, he noted, may also boost shrews\u2019 ability to sniff out prey such as earthworms.<\/p>\n
The researchers said a third possible explanation was mechanical reinforcement of the snout, allowing the shrew to process tougher prey when food is scarce \u2013 although they found little evidence to support this.<\/p>\n