Long-clawed shrews may increase the size of their snouts during winter months, according to new research. This adaptation, termed the 'reverse Dehnel's phenomenon', was observed in a study of shrew skulls from Japan.
While other small mammals, including common shrews and European moles, are known to reversibly shrink their body mass, skull size, and brain mass in winter – a process known as Dehnel's phenomenon – long-clawed shrews appear to show an opposite trend for their snouts.
Dr Yugo Ikeda, first author of the research from Toyo University, and his colleagues examined 136 long-clawed shrew skulls collected between 1948 and 1988. They found that shrews collected between January and April had a brain case height 12% smaller than younger shrews from August to September. However, the snout's height was 7% larger and its width 6% greater in winter specimens.
The researchers suggest that an expanded nasal cavity could create more space for a vascular network, which might warm freezing air before it reaches the brain, helping to maintain cognitive functions. An enlarged nasal cavity may also improve the shrews' ability to detect prey.
The team noted these changes were reversible, with brain case height increasing in shrews that survived winter. Conversely, snout width, but not height, was smaller in these shrews.