The Cu­ri­ous Case of the Gro­lar Bear

With changes in the Arc­tic climes come north-south species hy­bridiza­tion and the po­ten­tial for strange new ge­netic brews

Canadian Wildlife - - CONTENTS - By Kerry Banks

With changes in the Arc­tic climes come north-south hy­bridiza­tion and strange new ge­netic brews

When bi­ol­o­gists Jodie Pon­gracz and Evan Richard­son flew to Canada’s Arc­tic to cap­ture and tag po­lar bears in the spring of 2012, they came across a star­tling sight — a po­lar bear strolling be­side an­other bear with cho­co­late brown fur on its legs, a brown stripe down its back and a flat con­cave face and head that looked like it had been trans­planted from a griz­zly. This un­likely duo was sighted at lat­i­tude 73 de­grees north, on a frozen arm of the Arc­tic Ocean near Vic­to­ria Is­land — hun­dreds of kilo­me­tres north of where griz­zlies are nor­mally found.

Two years later, Pon­gracz and Richard­son cap­tured the same an­i­mal and took a DNA sam­ple. It was de­ter­mined that the bear was a hy­brid, or what some have dubbed a “gro­lar,” pro­duced by the mat­ing of a fe­male po­lar bear and a male griz­zly. This was not an iso­lated case. Gro­lars have been spot­ted in this part of the Cana­dian Arc­tic dat­ing back to 2006, when a hunter shot one of these cross­breeds on Banks Is­land in the North­west Ter­ri­to­ries. Af­ter view­ing its car­cass, the lo­cal Inuit al­lowed how they had no word for this crea­ture in their lan­guage.

Some sci­en­tists have spec­u­lated that gro­lars and other hy­brids may be the ad­vance guard of a strange new ge­netic brew of Arc­tic species that will be­gin to emerge as global warm­ing re­moves the icy bar­ri­ers that once kept dif­fer­ent species apart. Al­though the ev­i­dence re­mains sketchy, hy­bridiza­tions have also been re­ported between harp and hooded seals, At­lantic wal­rus and Pa­cific wal­rus, nar­whals and bel­u­gas, and right whales and bow­head whales.

There is no doubt that the re­duc­tion of sea ice in the Arc­tic is go­ing to usher in pro­found eco­log­i­cal changes. Hy­bridiza­tion will be one of them. As Bren­dan Kelly, a marine bi­ol­o­gist at the Univer­sity of Alaska Fair­banks and ex­ec­u­tive di­rec­tor of the Study of En­vi­ron­men­tal Arc­tic Change, notes, “In the case of Arc­tic species, you’ve had a con­ti­nent-size mass of sea ice keep­ing species iso­lated for thou­sands of years. If you re­move that bar­rier, you can re-es­tab­lish con­tact. Right now, the sea ice is melt­ing quite rapidly, so we’re go­ing to see a lot of pre­vi­ously iso­lated pop­u­la­tions come into con­tact. We’re likely to see a lot more hy­bridiza­tion.”

In 2010, Kelly and two other Amer­i­can sci­en­tists, An­drew White­ley and David Tall­mon, pub­lished an ar­ti­cle in the jour­nal Na­ture in which they cited 34 op­por­tu­ni­ties for hy­bridiza­tion across 22 Arc­tic or near-arc­tic species. These were based on an­i­mals’ ge­netic com­pat­i­bil­ity and ge­o­graphic range.

In cer­tain cases, such as in­ter­breed­ing between North At­lantic and North Pa­cific minke whales, the crossovers would not re­sult in a loss of bio­di­ver­sity, notes Kelly. In other in­stances, such as between bow­head whales and rare North Pa­cific right whales, whose pop­u­la­tion is es­ti­mated at fewer than 200, in­ter­breed­ing could lead to ex­tinc­tion of the smaller pop­u­la­tion.

Not all cross-species mat­ings pro­duce vi­able off­spring, but the chances are bet­ter in Arc­tic marine mam­mals, says Kelly, be­cause their num­ber of chro­mo­somes has changed lit­tle over time. This is cer­tainly true of cetaceans, says Carla Cross­man, a marine mam­mal ge­neti­cist with Ocean­wise, a global con­ser­va­tion pro­gram. She says there are 18 to 20 known crosses among cetaceans.

For now, most sci­en­tists don’t view hy­bridiza­tion as a ma­jor threat to bio­di­ver­sity. “The dan­gers are real — if un­qual­i­fied,” notes Marco Festa-bianchet, a pro­fes­sor of bi­ol­ogy at Que­bec’s Univer­sité de Sher­brooke, who co-chaired a group of wildlife ex­perts with the Com­mit­tee on the Sta­tus of En­dan­gered Wildlife in Canada in 2010 that tried to come up with rec­om­men­da­tions on how to deal with hy­bridiza­tion. “While we can gen­er­ally pre­dict that some species will move north, pre­dic­tions of when, where and how are very im­pre­cise.”

In re­cent years, red fox, white-tailed deer, Pa­cific salmon and killer whales have all be­gun ap­pear­ing in the Arc­tic. The or­cas’ big dor­sal fins, which im­pede nav­i­ga­tion in ice-choked wa­ters, had pre­vi­ously kept them from the re­gion, but that has changed with the warm­ing cli­mate. Aside from in­creas­ing the chances of hy­bridiza­tion, the sud­den en­try of an apex preda­tor could have a ma­jor im­pact on the re­gion’s ecol­ogy: or­cas have been ob­served at­tack­ing and eat­ing bel­u­gas and nar­whals.

Bar­ren-ground griz­zly bears are also mov­ing north­ward, and they seem to be thriv­ing. As An­drew De­rocher, a bi­ol­o­gist at the Univer­sity of Al­berta and a world author­ity on po­lar bears, ex­plains, “The cli­mate has warmed, there is enough food for them, and there are fewer griz­zlies be­ing shot as the Inuit life­style shifts from hunt­ing and trap­ping to a wage econ­omy.” At the same time, po­lar bears are at risk: most of their hunt­ing for seals is on the ice dur­ing win­ter, so now they are spend­ing more time on land as the sea ice re­cedes, caus­ing them to lose body weight and de­cline in num­bers.

Bear hy­brids in the Arc­tic would most likely be pro­duced by male griz­zlies trav­el­ling and mat­ing with fe­male po­lar bears be­cause male griz­zlies emerge ear­lier from win­ter hi­ber­na­tion and head out in search of food while the fe­males tend to stay close to home. Such li­aisons, ex­plains De­rocher, would not be ca­sual en­coun­ters, as it takes sev­eral days to sev­eral weeks of fre­quent cop­u­la­tion to in­duce ovu­la­tion in fe­male po­lar bears. How well-adapted such hy­brids would be to Arc­tic con­di­tions is un­known. Po­lar-griz­zly hy­brids in a Ger­man zoo ex­hib­ited be­hav­iour as­so­ci­ated with seal hunt­ing but did not pos­sess the strong swim­ming abil­i­ties of po­lar bears.

An­other per­plex­ing ques­tion — the source of this mys­te­ri­ous clus­ter of bear hy­brids — was re­cently an­swered by DNA anal­y­sis. Ac­cord­ing to a study headed up by Pon­gracz and Richard­son and re­ported in a 2016 is­sue of the sci­en­tific jour­nal Arc­tic, all of the eight doc­u­mented cases of hy­bridiza­tion — four first-gen­er­a­tion hy­brids and four sec­ond-gen­er­a­tion “back­crosses” — can be traced to one fe­male po­lar bear that mated with two griz­zly males. That fe­male and three of her off­spring have since been killed, leav­ing the re­searchers to won­der if this spate of hy­brids is merely a blip caused by the ac­tions of one mate-less fe­male po­lar bear, or if this type of un­usual mat­ing sig­nals the start of the break­down of species bar­ri­ers.

“We don’t know if there are other hy­brids run­ning around out there,” ad­mits Richard­son, a po­lar bear re­search sci­en­tist with En­vi­ron­ment and Cli­mate Change Canada. “Three of the hy­brid cubs (all of them male) may still be alive, and if they take af­ter their fa­ther’s taste in part­ners, then more hy­brids could be pro­duced.”

The odds of these bears’ sur­vival may be re­duced sim­ply be­cause their cu­ri­ous fea­tures make them at­trac­tive tro­phies. “Their pelts can be sold for a good price,” says De­rocher.

As for the ques­tion of whether we can ex­pect to see more hy­brid bears, De­rocher is un­sure. “What this means in the longer term is im­pos­si­ble to say. It’s very dif­fi­cult to pre­dict the path of evo­lu­tion.”

What De­rocher is more cer­tain about is the bleak fu­ture of po­lar bears. He ex­pects them to dis­ap­pear from their present ranges long be­fore their genes are swamped by those of griz­zly bears. “The best es­ti­mates in­di­cate that we’ll prob­a­bly lose some­where around two-thirds of the world’s pop­u­la­tion around mid-cen­tury, just based on the sim­ple fact that we’re los­ing sea ice,” says De­rocher. “No sea ice means no seals. And no seals means no po­lar bears.”a

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ANOM­ALY OR HAR­BIN­GER All eight cases of “gro­lar bear” hy­bridiza­tion that have been doc­u­mented can be traced to one fe­male po­lar bear that mated with two griz­zly males

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