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Borneo's orangs have rocky past: endangered today, the apes have been to the brink before.

Orangutans on the island of Borneo descend from a relatively small number of ancestors who apparently squeezed through a rough patch about 176,000 years ago, according to the broadest genetic analysis to date of their species.

The genetic data suggest an ancient population bottleneck in which animal numbers shrank and then expanded once conditions improved, says anthropological geneticist Natasha Arora of the University of Zurich.

A serious chill gripped the planet roughly 190,000 to 130,000 years ago, Arora and her colleagues point out in a paper posted online November 22 in the Proceedings of the National Academy of Sciences. Borneo itself wasn't iced over, but rain forests where orangutans live might have shrunk during this time, constraining the orangutan population.

Orangutans today live only on Borneo and Sumatra, in two endangered species that diverged several million years ago. The new genetic findings are "very surprising" in light of the ancient split, says Lounes Chikhi, a population geneticist in Toulouse, France, with the CNRS research agency.

"Something really important happened" roughly 170,000 years ago, Chikhi says. That something doesn't seem to have bottlenecked gibbons and macaques that shared ancient Borneo with the orangutan Pongo pygmaeus. But at least one other primate may have had a history similar to Borneo's orangutans. "There is a strange parallel with human evolution," Chikhi says. Based on mitochondrial DNA, the most recent common maternal ancestor among modern humans lived 170,000 years ago. "What happened between 150,000 and 200,000 years ago that influenced both Homo sapiens and Pongopygmaeus?" he asks.

Evidence for the orangutan bottleneck turned up thanks to 17 researchers who isolated DNA from fecal and hair samples of 211 wild orangutans at 12 sites and built a genetic family tree from the data.

A bottleneck maybe the simplest explanation for the recent shared ancestry of Borneo's orangutans, says Jakarta-based conservation scientist Erik Meijaard of People & Nature Consulting International. But some more complex scenario involving extinctions and repopulations might also fit the data.

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The study also fuels some conservationists' worries by confirming that female orangutans don't move much, with rivers in particular being a big barrier. So what may look to a human like a fine stretch of rain forest for orangutans may in reality be impossible for them to reach.

"Once you've lost orangutans from a watershed," Meijaard says, "they're gone."

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Title Annotation:Life; orangutans
Author:Millus, Susan
Publication:Science News
Geographic Code:9INDO
Date:Dec 18, 2010
Words:395
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