科学美国人60秒:Birds Roost on New Evolutionary Tree

In a massive data crunching analysis, researchers have created a new evolutionary tree for birds. The effort required enormous computing power and new algorithms because it involved the whole genomes, rather than just a few genes, of 48 species of birds to establish their relatedness. The study is the first of its kind for vertebrates.

“It contradicts morphology-based trees. It contradicts mitochondrial trees. It supports more trees based upon nuclear genes, although those trees weren’t highly resolved and this one is.”
Erich Jarvis of the Howard Hughes Medical Institute and Duke University Medical Center, one of the leaders of the whole genome sequence analysis effort. Multiple papers related to this work are in the December 12th special issue of the journal Science. [Guojie Zhang, Erich D. Jarvis and M. Thomas P. Gilbert, A flock of genomes]

Jarvis previewed the studies in a talk he gave October 19th at the ScienceWriters2014 meeting in Columbus, Ohio:

“We decided we wanted to make a big effort to focus on birds, because each of us had some aspects that we liked about bird biology. But something was practical about that as well. Bird genomes, in terms of genome size, compared to other vertebrate groups like reptiles, amphibians, mammals, they’re on average smaller than other vertebrates. And this allows one to sequence their genomes easier, and also assemble them easier. The reason why: it’s thought that they have less repetitive genome in their genome, but yet a similar complement of genes encoding for proteins…so you can learn a lot about vertebrate biology more easily studying birds than you can in other groups where there’s a lot of this repetitive so-called junk DNA. “

Some of the major findings of the new bird tree:

“We can infer at least two independent gains of vocal learning…we’re also supporting two independent gains of water adaptions…and two independent origins of the predatory trait, suggesting that amongst this higher land-bird group that includes songbirds, parrots, hawks, eagles, falcons and so on, a top apex predator was the common ancestor of the higher land birds that most of you know about, including vocal learners.

“What’s also different compared to a number of trees that have been dated with fossils, with the whole genome scale dating we are arguing that avian diversity of 95 percent of the species did not occur 80 to 100 million years ago in the Cretaceous Period, but occurred right around the time of the extinction of the dinosaurs [what we call the meteor impact in the Yucatan peninsula], which was an alternative theory…right after that extinction event, we get all orders of birds diverge within 50 million years. And then from there on everybody else speciates.”

—Steve Mirsky