Cousin Who? Gliding mammals may be primates’ nearest kin

Hey, primates, meet the colugos—two little-known species of small rain forest mammals now presented as your next of kin.

NEARLY PRIMATE. Possibly one of the two living species closest to primates, a Malaysian colugo mother shelters a youngster. A colugo leaping off a tree (inset) snaps open a membrane for prodigious gliding powers. N. Lim/National Univ. Singapore

With one species native to the Philippines and the other to Southeast Asia, colugos can stretch out a membrane that lets them leap off trees and glide some 70 meters.

They’ve landed on the nearest surviving evolutionary branch to primates’, suggests a new genetic analysis by William Murphy of Texas A&M University in College Station and his colleagues. The researchers added a novel twist by looking at rare genetic glitches as well as familiar genes.

“Having the closest relative really allows us to understand the change of events that led to primates,” says Murphy. That in turn feeds efforts “to better understand the changes that make us human.”

The dawn of primates has been hard to figure out, Murphy says, because big lineages have split and resplit so fast, from an evolutionary standpoint, that branches had little time to accumulate telltale differences before splintering further. Recent research suggests that tree shrews, colugos, and primates descended from a common ancestor, but scientists have not been able to agree on the order in which these branches diverged.

Murphy and his colleagues have now searched 36 animal genomes for rare glitches called indels, short stretches of DNA that appear in some genomes and are absent from others. Murphy points out that it’s unlikely for an indel to have occurred independently in exactly the same place in two species.

The researchers found seven indels shared by colugos and primates but not seen in the other mammals. They found only one indel that’s shared by just tree shrews and primates. That pattern supports the notion that the tree shrew lineage branched away first, leaving colugos as our nearest cousins, Murphy and his colleagues conclude in the Nov. 2 Science.

The team also created a more traditional family tree, based on DNA sequences from a range of mammals, which showed the same pattern.

“In short, yes, I buy it,” says Anne Yoder, who directs the Duke Lemur Center in Durham, N.C. She says that she’d like to see more species included in the analysis but calls the methodology “quite sound.”

Morphologists sound less enthusiastic. Jonathan Bloch of the Florida Museum of Natural History in Gainesville and Mary Silcox of the University of Winnipeg in Manitoba say that they agree with Murphy’s arrangement of fossils but are not completely convinced by his placements of living species.

Eric Sargis of Yale University says that some 30 evolutionists are collaborating on the biggest study yet of mammal relationships, which may overwhelm all previous research.

Susan Milius is the life sciences writer, covering organismal biology and evolution, and has a special passion for plants, fungi and invertebrates. She studied biology and English literature.

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