Bird tree tells new tale of evolution

Using the world’s first family tree linking every known bird species, scientists, including two at Simon Fraser University, have discovered that birds appear to be accelerating their rate of evolution. The finding is contrary to the scientists’ expectations.

They spent five years creating their tree, using millions of years worth of fossil data stretching back to the Age of the Dinosaurs, DNA data and supercomputers. They then mapped where on Earth and when in history birds’ diversification took place.

A new paper in the journal Nature contains the scientists’ profile of how 9 993 bird species currently alive globally made it to where they are today. Based on previous studies, the researchers expected to see bird speciation slowing down through time.

But SFU biologist Arne Mooers, Jeff Joy, a postdoctoral fellow in his lab, and researchers at Yale University, University of Sheffield and University of Tasmania have discovered birds’ speciation rate is increasing, not declining.

Different theories

“Perhaps birds are special,” theorizes Mooers. “Maybe they’re so good at getting around they can escape local competition from relatives and start anew elsewhere, producing bursts of new species at different times and in different parts of the globe.”

The authors have also discovered that birds’ speciation rate doesn’t drop off the further they are from the equator. Since three quarters of all birds are found near the equator, it was expected that speciation there would be more common.

“We know the tropical biome has been shrinking during the last 15 million years,” says Joy. “Perhaps, just as bushtits bunch together closely at night, bird species have clustered together in the tropics as their habitat shrunk.”

“We need to think a lot more about how Earth’s changing climate has led to current distributions,” says Mooers. “It’s a lovely conundrum.”

Unfortunately, birds’ rosy speciation history doesn’t nullify the fact that they can’t outfly their growing human-induced rate of extinction. Researchers estimate that birds have recently been proliferating at a rate of about one new bird species every 700 years. Meanwhile, they estimate birds’ recent human-caused extinction rate to be about 300 times higher.

(EurekAlert, November 2012)

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