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Vol. 343 ,
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Obscure Glider Proves to Be Primate's Closest Cousin
1 November 2007 (All day)
The flying lemur's name is a misnomer: It's neither a true lemur, nor can it fly. Nonetheless, this relatively rare, squirrel-sized native of Southeast Asian rain forests has just glided into the limelight. A comprehensive genetic analysis shows that the misnamed mammal is our closest nonprimate cousin. As such, researchers will need to pay more heed to flying lemurs as they try to envision the ancestor of all primates.
Most taxonomists agree that primates--apes, humans, monkeys, and real lemurs--belong to a larger group called Euarchonta, which also includes flying lemurs and tree shrews. But they have had trouble sorting out just how all of the species are related. Usually, researchers distinguish which species evolved first by comparing the same piece of DNA from each one--more differences signal a more ancient split. But Euarchonta mammals evolved within such a short period of time that the counts yield different answers, depending on the particular analysis or DNA studied. Some research indicates that the tree shrew is closest to primates; other studies tap the flying lemur. A few even suggest that flying lemurs and tree shrews are a group unto themselves within Euarchonta.
Jan Janecka, a postdoctoral fellow working with evolutionary genomicist William Murphy at Texas A&M University in College Station, has now jumped into the debate with a two-pronged molecular study, the most comprehensive approach attempted thus far. He, Murphy, and their colleagues first looked for matches to 197,522 pieces of human genes in a variety of other mammals. They compared those matches to pick out short pieces of DNA that had been added or lost in one or more species. Species that share these so-called indels likely have a common ancestor and are more closely related than species lacking a particular indel. The researchers also analyzed parts of 19 genes, looking for changes in the DNA sequence from one species to the next.
Both analyses brought flying lemurs closer to primates than they had ever been before. Seven indels are shared by primates and flying lemurs but not tree shrews, suggesting a close kinship between those first two groups, Janecka and colleagues report tomorrow in Science. Only one indel was common to primates and tree shrews but not flying lemurs, and no indels suggested that flying lemurs and tree shrews were their own subgroup. The gene studies likewise tagged flying lemurs as the closest primate relative.
"The analysis is well-done; the data are rock solid. I think people will buy it," says Anne Yoder, an evolutionary biologist at Duke Lemur Center in Durham, North Carolina. Next, she says, researchers should fully sequence the flying lemur genome to better understand primate evolution. "Then you can hypothesize what the common ancestor looked like," she explains. For her part, Yoder intends to incorporate the flying lemur in her own studies of the relationships among true lemurs and their relatives. That will require her getting her hands on some flying lemur samples. "I don't have any tissue in my freezer," she says, "but I am certainly going to try to get some."