Natures wonders: energy and shrew brains (Introduction)

by David Turell @, Tuesday, October 24, 2017, 17:20 (983 days ago) @ David Turell

Shrews shrink skull and brain size in winter to conserve energy. Brains take 20% of human energy; other mammals must follow the same metabolic pattern, although their brains are smaller and their metabolic costs lower:

"Writing in the journal Current Biology, researchers led by Javier Lazaro of the Max Planck Institute for Ornithology in Germany report that the red-toothed shrew (Sorex araneus) reduces its head size on an annual basis. At the same time, its brain mass decreases by up to 30% and several major organs, as well as the spine, also grow smaller.

"The researchers speculate that the bizarre phenomenon might be a survival strategy. The shrews have very high metabolisms, but neither migrate nor hibernate when temperatures fall and food becomes scarce.

"'Reducing head size -- and thus brain size -- might save energy disproportionally as the brain is energetically so expensive," Lazaro says.

"The research has so far failed to uncover the cause of the head shrinkage, although the mechanism appears to be the absorption of tissue within cranial sutures.

"The fact that the rodents tended to have smaller heads in winter was first observed in 1949 by a Polish mammologist called August Dehnel – leading to the shrinkage being termed Dehnel’s phenomenon.

"However, Lazaro and his colleagues are the first to document the reduction and expansion of individual shrews by following them around for an entire year.

"The team captured 12 wild shrews, anaesthetised them, X-rayed their skulls, implanted microchips, and then released them. Using live traps, the rodents were periodically re-captured and X-rayed again. The scientists found that head size was smallest during winter, but regrew through spring.

"Earlier studies had suggested that Dehnel’s phenomenon might be more apparent than real, the result of shrews with larger heads simply dying off during the colder months and leaving their better adapted little brethren to carry on.

"Lazaro and his colleagues disprove the idea.

"'This means every single individual undergoes this change every winter, which remains baffling to us," he says."

Comment: Brains use lots of energy. This is an unusual adaptation to for the problem, but there is less food in winter. How the adaptation developed is unknown, but it involved reabsorption of skull plates which may have forced brain shrinkage. It is so massive a change it is akin to speciation. Research into this mechanism may unearth some information about speciation. And, if God arranges for new species, this may afford an insight into His methods.

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