Mapping the "big bang" of bird evolution.

• Author: Chi, Kelly Rae
• Position: Science & Technology

THE GENOMES of modern birds tell a story of how they emerged and evolved after the mass extinction that wiped out dinosaurs and almost everything else 66,000,000 years ago. That story now is coming to light thanks to an ambitious international collaboration that has been underway for almost five years. Scientists already knew that the birds who survived the mass extinction experienced a rapid burst of evolution, but the family tree of modern birds has confused biologists for quite a long time and the molecular details of how birds arrived at the spectacular biodiversity of more than 10,000 species is barely known.

To resolve these fundamental questions, the Avian Phylogenomics Consortium--led by Guojie Zhang of the National Genebank at BGI in China and the University of Copenhagen; Erich D. Jarvis of Duke University and the Howard Hughes Medical Institute; and M. Thomas P. Gilbert of the Natural History Museum of Denmark--has sequenced, assembled, and compared full genomes of 48 bird species, including the crow, duck, falcon, parakeet, crane, ibis, woodpecker, eagle and others, representing all major branches of modern birds.

"[We have been able] to answer numerous fundamental questions to an unprecedented scale," says Zhang. "This is the largest whole genomic study across a single vertebrate class to date."

Adds Gilbert: "Although an increasing number of vertebrate genomes are being released, to date no single study has deliberately targeted the full diversity of any major vertebrate group. This is precisely what our Consortium set out to do. Only with this scale of sampling can scientists truly begin to fully explore the genomic diversity within a full vertebrate class."

"This is an exciting moment," relates Jarvis, a neuroscientist. "Lots of fundamental questions now can be resolved with more genomic data from a broader sampling. I got into this project because of my interest in birds as a model for vocal learning and speech production in humans, and it has opened up some amazing new vistas on brain evolution."

This first round of analyses suggests some remarkable new ideas about bird evolution, as it presents a well-resolved new family tree for birds, based on whole-genome data. A second flagship paper describes the big picture of genome evolution in birds. Six other papers in a special issue of Science describe how: vocal learning may have evolved independently in a few bird groups and in the human brain's speech regions; the sex chromosomes of birds came to be; birds lost their teeth; and crocodile genomes evolved as well as ways in which singing behavior regulates genes in the brain-while a new method for phylogenic analysis with large-scale genomic data was developed.

Previous attempts to reconstruct the avian family tree using partial DNA sequencing or anatomical and behavioral traits have met with contradiction and confusion. Because modern birds split into species early and in such quick succession, they did not evolve enough distinct genetic differences at the genomic level to determine their early branching order clearly. To resolve the timing and relationships of modern birds, the Consortium authors used whole-genome DNA sequences to infer the bird species tree.

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