201517Jan14:47

Polar bears are shift­ing to areas with more sea ice

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pub­lished 17 Jan­u­ary 2015 | mod­i­fied 17 Jan­u­ary 2015
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In a new polar bear study pub­lished on 6 Jan­u­ary in the jour­nal PLOS ONE , sci­en­tists from around the Arc­tic have shown that recent gen­er­a­tions of polar bears are mov­ing towards areas with more per­sis­tent year-​round sea ice.

Polar bear clusters geneflowThe goal of the study was to see how genetic diver­sity and struc­ture of the world­wide polar bear pop­u­la­tion have changed over the recent dra­matic decline in their sea-​ice habi­tat. The sci­en­tists, led by the U.S. Geo­log­i­cal Sur­vey (USGS), found that the 19 rec­og­nized sub­pop­u­la­tions of polar bears group into four genetically-​similar clus­ters, cor­re­spond­ing to eco­log­i­cal and oceano­graphic fac­tors. These four clus­ters are the East­ern Polar Basin, West­ern Polar Basin, Cana­dian Arch­i­pel­ago, and South­ern Canada.

The sci­en­tists also detected direc­tional gene flow towards the Cana­dian Arch­i­pel­ago within the last 13 gen­er­a­tions. Gene flow of this type can result from pop­u­la­tions expand­ing and con­tract­ing at dif­fer­ent rates or direc­tional move­ment and mat­ing over gen­er­a­tions. The find­ings of these geo­graph­i­cal clus­ters and direc­tional gene flow are impor­tant because they sup­port the hypoth­e­sis that the species is merg­ing in the spe­cific part of the Arc­tic that most likely will retain sea ice into the future.

The polar bear’s recent direc­tional gene flow north­ward is some­thing new. In our analy­ses that focused on more his­toric gene flow, we did not detect move­ment in this direction.
Eliz­a­beth Pea­cock, lead author, USGS researcher »

The study found that the pre­dom­i­nant gene flow was from South­ern Canada and the East­ern Polar Basin towards the Cana­dian Arch­i­pel­ago where the sea ice is more resilient to sum­mer melt due to cir­cu­la­tion pat­terns, com­plex geog­ra­phy, and cooler north­ern latitudes.

Pro­jec­tions of future sea ice extent in light of cli­mate warm­ing typ­i­cally show greater reten­tion of sea ice in the north­ern Cana­dian Arch­i­pel­ago than in other regions.

By exam­in­ing the genetic makeup of polar bears, we can esti­mate lev­els and direc­tions of gene flow, which rep­re­sents the past story of mat­ing and move­ment, and pop­u­la­tion expan­sion and con­trac­tion,” said Pea­cock. “Gene flow occurs over gen­er­a­tions, and would not be detectable by using data from satellite-​collars which can only be deployed on a few polar bears for short peri­ods of time.”

Spring 2014USGS sci­en­tists con­duct a health eval­u­a­tion of a young male polar bear in the Arc­tic as part of the annual south­ern Beau­fort Sea pop­u­la­tion sur­vey. The bear is sedated for approx­i­mately an hour while the team records a vari­ety of mea­sure­ments and col­lects key bio­log­i­cal sam­ples. The annual pop­u­la­tion sur­vey has been con­ducted since the mid-1980’s and helps gauge the over­all health of the Polar Bear population:


(Source: USGS YouTube chan­nel, 15.12.2014)


The authors also found that female polar bears showed higher fidelity to their regions of birth than did male polar bears. Data to allow com­par­i­son of the move­ments of male and female polar bears is dif­fi­cult to obtain because male bears can­not be col­lared as their necks are wider than their heads.

The study also con­firmed ear­lier work that sug­gests that mod­ern polar bears stem from one or sev­eral hybridiza­tion events with brown bears (see also “No evi­dence of brown bear ances­try in polar bears, new DNA study says”). No evi­dence of cur­rent polar bear-​brown bear hybridiza­tion was found in the more than 2,800 sam­ples exam­ined in the cur­rent study. Sci­en­tists con­cluded that the hybrid bears that have been observed in the North­ern Beau­fort Sea region of Canada rep­re­sent a recent and cur­rently local­ized phe­nom­e­non. Sci­en­tists also found that polar bear pop­u­la­tions expanded and brown bear pop­u­la­tions con­tracted in peri­ods with more ice. In peri­ods with less ice, the oppo­site was true.

This cir­cum­po­lar, multi-​national effort pro­vides a timely per­spec­tive on how a rapidly chang­ing Arc­tic is influ­enc­ing the gene flow and likely future dis­tri­b­u­tion of a species of world­wide con­ser­va­tion concern.



(Source: USGA news release, 06.01.2015)


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Tiger range countries map

Tiger map” (CC BY 2.5) by Sander­son et al., 2006.

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