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Evo­lu­tion


A Col­lec­tion of News by Moos


201411Jul16:54

Evo­lu­tion­ary his­tory of bears – New insights

Infor­ma­tion
pub­lished 11 July 2014 | mod­i­fied 11 July 2014
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Bear networksAccord­ing to researchers of the LOEWE Bio­di­ver­sity and Cli­mate Research Cen­tre (BiK-​F), Goethe Uni­ver­sity Frank­furt and the U.S. Wildlife Ser­vice sev­eral bear species that today only occur in Amer­ica or in Asia have hybridised in their evo­lu­tion­ary his­tory. The Beringia land bridge, which in for­mer times con­nected the habi­tats of these species, might have enabled their encounter. The large-​scale study is based on the com­par­i­son and analy­sis of genetic mate­r­ial of all bear species that still exist. The results have been pub­lished online on 5 June in the jour­nal Evo­lu­tion and Mol­e­c­u­lar Biology.

If in doc­u­men­taries or in the zoo – everyone has seen and knows about brown bears, polar bears and pan­das. How­ever, there are sev­eral other bear species in Asia and South Amer­ica that are less well-​known, such as the sloth bear, the Asian or the spec­ta­cled bear. There are eight bear species that still exist world­wide. Despite many years of research, the exact rela­tion­ships between them remain unresolved.


In Osnabrück Zoo two hybrid bears twins (mother Brown Bear, father Polar Bear) are liv­ing. Until 2004 the Zoo kept three species of bears together and this is the result:


(Source: ChristinaM2007 YouTube Channel)

Who with whom? Polar bear and brown have hybridised
Pre­vi­ous analy­ses of genetic mate­r­ial of polar bears and brown bears have proven already that the two species have hybridised dur­ing their long evo­lu­tion­ary his­tory. This behav­iour can still be observed today and the ongo­ing cli­mate change dri­ves the bear even closer. It is there­fore likely that there have been sim­i­lar exchanges of genetic mate­r­ial between other species of the bear family.

… as well as brown bears and black bears
To shed light on this, a team of the Ger­man Bio­di­ver­sity and Cli­mate Research Cen­tre (BiK-​F) and the Goethe Uni­ver­sity Frank­furt in coop­er­a­tion with col­leagues from the US have now analysed cer­tain genome parts of all bear species alive today. “We were able to show that sev­eral bear species have hybridised dur­ing their evo­lu­tion­ary his­tory. The exchange can still be traced in the genetic makeup of today’s bears,” says the lead author of the study, Ver­ena Kutschera (BiK-​F). This mix-​up makes it dif­fi­cult to clas­sify some gene frag­ments as belong­ing to a par­tic­u­lar species.

Beringia land bridge serv­ing as an inter­con­ti­nen­tal meet­ing point
Sur­pris­ingly, sev­eral bear species which nowa­days live on dif­fer­ent con­ti­nents have also taken part in the mat­ing and thus gene exchange. This may have been pos­si­ble because the sig­nif­i­cantly lower sea level dur­ing past ice ages resulted in a land bridge between Asia and North Amer­ica, the Beringia land bridge. Thus the ances­tors of today’s bear species, e.g. of the Asian black bear and the Amer­i­can black bear, had the oppor­tu­nity to meet and to mate.

Darwin’s species tree is insuf­fi­cient to map com­pli­cated rela­tion­ships
All eight bear species that occur today have well adapted to their present habi­tat and dif­fer phys­i­cally very much. A prime exam­ple for this is polar bears and black bears. Nev­er­the­less, the spe­ci­a­tion of some indi­vid­ual genes has not fin­ished yet which addi­tion­ally com­pli­cates the research of the evo­lu­tion of bears.

With new mol­e­c­u­lar meth­ods more gene parts might be dis­cov­ered in the genomes of mam­mal species that could orig­i­nate from other species. Appar­ently sep­a­rate genetic lin­eages turn out to have merged – some­times repeat­edly – dur­ing the evo­lu­tion­ary his­tory and exchanged genetic mate­r­ial with each other. “The tra­di­tional pedi­gree already used by Dar­win is not always suit­able to map evo­lu­tion­ary his­tory in full detail. So-​called phy­lo­ge­netic net­works are more use­ful to depict the genetic mix-​up that we have found “, com­ments evo­lu­tion­ary biol­o­gist Prof. Dr. Axel Janke, BiK-​F, leader of the research team. The study demon­strates that evo­lu­tion often is not a lin­ear process; thanks to mod­ern mol­e­c­u­lar meth­ods it’s com­plex processes are finally revealed.



(Source: Senck­en­berg press release, 11.06.2014)


Goal: 7000 tigers in the wild

Tiger range countries map

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

about zoos and their mis­sion regard­ing breed­ing endan­gered species, nature con­ser­va­tion, bio­di­ver­sity and edu­ca­tion, which of course relates to the evo­lu­tion of species.
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