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In Sweden, the beavers are all cousins.

Although biologists have long thought that a species needs genetic variation in order to thrive (SN: 9/25/93, p.200), beavers are proving this assumption wrong. Supposedly, variation ensures that individuals can adapt to varying living conditions. Also, even if one individual's immune system can't fend off a particular infection, another individual's slightly different system can. But Castor fiber seems to do just fine without this variation, says Hans Ellegren from the Swedish University of Agricultural Sciences in Uppsala.

Hunters killed off Sweden's beavers during the 1800s. Then, during the 1920s and 1930s, conservationists reintroduced a small number of Norwegian animals, of which 46 survived in 11 locations in Sweden. The Swedish beaver population now numbers 100,000, says Ellegren. In Sweden, he and his colleagues obtained DNA from 31 beavers, 25 that lived in the same river system and six from varying distances away. They also examined genetic material from 15 Norwegian beavers and six Russian ones.

The researchers compared the animals' major histocompatibility complex (MHC) genes, highly variables sections of DNA that enable organisms to fight many kinds of pathogens. They observed that none of the beavers showed much diversity in their MHC genes.

The Swedish animals proved as genetically identical as populations of animals restricted to small islands, where incestuous matings often occur, the researchers reported in the Sept. 1 PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES. The Norwegian animals didn't prove any more diverse. Beavers may be able to tolerate the negative effects of inbreeding because they naturally live in small colonies and never move beyond their native river, the scientists propose. However, genetic differences among the DNA "fingerprints" of the Russian beavers show that this species does posses genetic variation.
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Title Annotation:genetic variation research on beavers
Publication:Science News
Article Type:Brief Article
Date:Oct 9, 1993
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