Wednesday, 25 October 2017

Shrews' Heads (and Brains) Shrink As Seasons Change

By Mindy Weisberger, Senior Writer | October 23, 2017 01:40pm ET

In creatures with backbones, skulls get progressively bigger as the animal grows to maturity, but then tend to stay the same size thereafter. However, something happens to the skulls of adult red-toothed shrews that is exceedingly rare among vertebrates: The animals' heads shrink and expand in synch with seasonal changes.

For the first time, a team of researchers has documented the complete cycle of these dramatic changes in living Sorex araneus shrews, describing their findings in a new study published online today (Oct. 23) in the journal Current Biology.

The researchers captured X-ray images that recorded the shrunken and recovered states of the shrews' skulls and brains, finding that the animals' heads contracted by up to 20 percent in preparation for winter and ballooned back to their previous size over the spring and summer. [The World's 6 Smallest Mammals]

This shift in skull size— known as the Dehnel effect — was previously documented in studies of the skulls removed from deceased shrews. But this is the first evidence to track this remarkable adaptation in living animals over time and link it to other biological changes, the study authors reported.

For the new investigation, scientists captured 12 wild red-toothed shrews, so named because of a reddish tint in their front teeth caused by iron deposits in the enamel, according to a study published in 2006 in the Journal of Mammalogy.

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