2017-10-23 18:49:02
Trilobites: As Winter Sets In, Tiny Shrews Shrink Their Skulls and Brains

18:49, October 23 84 0

Bad news, bears. Hibernation is no longer the coolest thing animals do to survive the winter.

As cold weather approaches, tiny mole-like creatures known as red-toothed shrews will shrink their own heads, reducing their skull and brain mass by as much as 20 percent, according to new research published Monday in Current Biology. When warm weather returns, they will regrow the region nearly to its original size, giving new meaning to the phrase “spring ahead.”

Though it is not yet clear why the shrews go down a few sizes for the winter, the authors of the study speculate that the reduced head and brain size helps them conserve energy when resources are scarce.

“These tiny mammals cannot migrate long distances to avoid winter, nor can they enter any kind of energy-saving state” like hibernation, said Javier Lazaro, a doctoral student at the Max Planck Institute for Ornithology in Germany and an author of the study. They also have high metabolic rates and very little fat stored in their bodies. “Therefore, they starve within a few hours if they do not hunt constantly.”

The researchers say the shrinkage is a survival strategy.

“Brain tissue is energetically very expensive, so reducing overall brain size might decrease energy demands and thus food requirements,” he said.

The shrews’ reduction in size doesn’t only affect the head. Several major organs lose mass in winter, and the spine shortens, as well. Overall, the shrews in the study reduced their body mass by about 18 percent from July to February.

Previous research had hinted that all shrew species might undergo a reduction in body and head mass during the winter. There is even a term for it, Dehnel’s Phenomenon, named after the Polish zoologist who conducted that research, August Dehnel.

But previous studies only demonstrated the effect across whole populations of the small mammals, leaving open the possibility that larger-headed shrews were dying off in winter, reducing the average head size of the spring shrew populace.

To study individual shrews, the researchers used live traps to capture the animals in Germany from summer 2014 to fall 2015. The captured shrews were X-rayed and implanted with a microchip. Twelve shrews were captured and measured at three distinct intervals, each of them displaying the same pattern: a peak head size in summer, a cranial reduction in winter and then regrowth in spring.

About the size of a mouse and found in nearly all regions of the world, shrews are often mistaken for rodents, but are more closely related to moles. The red-toothed shrew is one of three existing species of shrews.

Exactly how a shrew shrinks its brain is still something of a head-scratcher. Changes in cranial size tend to be “unidirectional and finite” in vertebrates, the study notes. But there is evidence that the shrew’s brain case shrinks when the joints between the bones of the skull reabsorb tissue during autumn and winter. As spring approaches, the bone tissue regenerates.

The researchers could not say how the reduced brain size might affect the shrew’s cognitive abilities, and plan future research to learn more.

Knowing that a mammal can successfully shrink and regrow its own body — especially a complex organ like the brain — could open up exciting new avenues for exploration. Mr. Lazaro said that his team had already been approached by medical researchers with an interest in bone and joint diseases. The findings “could mean an important advance for the study of degenerative bone diseases such as osteoporosis,” he said.