Shrews it or lose it

Sci­en­tists dis­cover an in­cred­i­ble shrink­ing skull.

The Star Malaysia - Star2 - - Science - By WILL DUN­HAM

IT is not the tam­ing of the shrew, but rather the shrink­ing of the shrew.

Sci­en­tists this week de­scribed one of na­ture’s most in­trigu­ing phe­nom­ena, the shrink­age of the skull and body of a type of shrew as lean win­ter months ap­proach and the sub­se­quent re­growth of the crit­ters for the flow­er­ing of spring.

This ex­otic trait of the com­mon shrew, a tiny in­sect-eat­ing mam­mal in­hab­it­ing cen­tral and north Europe and a large part of Asia, was first noted in the 1940s but no pre­vi­ous re­search had stud­ied changes in in­di­vid­ual shrews.

The sci­en­tists pe­ri­od­i­cally caught, mea­sured and X-rayed wild shrews near the Ger­man vil­lage of Mog­gin­gen.

In­di­vid­ual shrews shrank their brain­case by up to 20% – 15% on av­er­age – from sum­mer to win­ter, then in the spring re­grew by up to 13% – 9% on av­er­age, not quite re­turn­ing to their orig­i­nal size.

Body mass also de­creased by win­ter and then in­creased in spring. Wild shrews live about 13-15 months and never re­gain their pre­vi­ous size.

“In these ex­tremely high meta­bolic an­i­mals, re­duc­ing body mass dur­ing win­ter, a pe­riod of re­source scarcity, might in­crease their sur­vival chances, as this would re­duce food re­quire­ments,” said evo­lu­tion­ary bi­ol­o­gist Javier Lazaro Tapia of the Max Planck In­sti­tute for Or­nithol­ogy in Ger­many.

“And re­duc­ing brain size, as well as other tis­sues, might save en­ergy as the brain tis­sues are en­er­get­i­cally so ex­pen­sive.

In other words, we are ob­serv­ing a win­ter­ing adap­ta­tion in terms of en­ergy sav­ing, an al­ter­na­tive strat­egy for a non-mi­gra­tory and non-hi­ber­nat­ing species.”

Com­mon shrews, whose favourite meal is earth­worms, are very ac­tive, and must eat con­stantly to sup­ply their ravenous metabolism.

They are ter­ri­to­rial and soli­tary, start­ing fierce fights when meet­ing other shrews, and tol­er­ate each other only dur­ing breed­ing sea­son.

Re­gard­ing the bi­o­log­i­cal mech­a­nisms be­hind the shrink­ing and re­growth, Lazaro said brain­case shrink­age is prob­a­bly achieved by a re­sorp­tion of tis­sue at the cra­nial su­tures, joints be­tween skull bones, with a re­gen­er­a­tion of bone tis­sue dur­ing the re­growth phase.

“If we think of our own skull and imag­ine it chang­ing in size by 20%, this is as­tound­ing and unimag­in­able,” Lazaro said.

“This im­age is what we want the reader to take home: how flex­i­ble seem­ingly rigid struc­tures can be if evo­lu­tion war­rants it, mak­ing this tiny high-power en­gine of an an­i­mal so suc­cess­ful.”

The re­search was pub­lished last week in the jour­nal Cur­rent Bi­ol­ogy. – Reuters

Is the com­mon shrew ca­pa­ble of adapt­ing its skull for the win­ter? Yes! — Reuters

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