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26-Jun-2008 14:00 Eastern US Time

Bird tree of life redrawn

CHICAGO—The biggest ever study of bird genes has redrawn their tree of life. The study challenges current classifications. It alters our understanding of how birds evolved. And it is a valuable new resource for phylogenetic and comparative bird studies.

Birds are among the most studied and best-loved of all animals. Much of what we know about animal biology comes from studies of birds.

But the bird tree of life - how the different species are related to each other - has been hard to figure out. A new research study with a snappy title - the Early Bird Assembling the Tree of Life Research Project - has just made a big difference.

How it was done

Based at Chicago's Field Museum, this project has been looking at DNA from all the main groups of birds that exist now. The scientists have built and studied a huge dataset of DNA sequences. These come from 19 different places in the DNA of each species, and from 169 different species.

The results of this enormous piece of research are published on June 27, 2008 in Science.

Recent technological advances made the research possible. These allow much larger pieces of a genome to be sampled, says Shannon Hackett. She is one of three lead authors and associate curator of birds at The Field Museum.

The research group sequenced 32000 bits of DNA for each species. This is about five times more data than in any previous study. The data were analysed using different methods and programs.

Moving the branches around

The study has given us "remarkable new understanding of the evolutionary relationships of birds", says Hackett. The results are so wide-ranging that the scientific names of dozens of birds will have to be changed. Biology textbooks and birdwatchers' field guides will need to be revised.

Here are a few of the surprises found by the new study: The widely-held view that shorebirds gave rise to all modern birds is wrong. Falcons are more closely related to songbirds than to other hawks and eagles. The closest relatives of grebes are flamingos. And flashy hummingbirds are just a specialised form of nighthawks, whose squat, bulky bodies make them an unlikely cousin.

There is a close and surprising connection between perching birds, on the one hand, and parrots and falcons on the other. This will change science's understanding of perching birds, the largest order of living birds.

The study has shown that distinctive lifestyles, such as nocturnal, raptorial and pelagic, have evolved several times.

Appearances are deceiving

The study has produced two major findings, says Sushma Reddy, another lead author and Bucksbaum postdoctoral fellow at The Field Museum. The first is that birds that look or act in a similar way are not necessarily related - "appearances can be deceiving."

Secondly, much of bird classification and "conventional wisdom on the evolutionary relationships of birds" is just plain wrong.

Hard relations

It has proved very difficult until now to figure out the evolution of birds. This is thought to be because modern birds appeared relatively quickly - within a few million years - during an explosive radiation 65-100 million years ago.

As a result many groups of similar-looking birds (owls, parrots, doves) have few if any living intermediate forms - birds that link them to other groups of birds. This makes it hard to decide how these groups are related to each other through evolution.

Many studies of bird evolution have given conflicting results. This new study is more robust because it has used large amounts of data from across the genome.

Robust tree for birds

Scientists from a number of universities around the world took part in the study. Much of the DNA sequencing and analysis was done in the Pritzker Laboratory for Molecular Systematics and Evolution at The Field Museum.

Birds are extremely diverse, Reddy says. "They are the largest of the tetrapod groups. Using this family tree we can begin to understand how this diversity originated, as well as how different bird groups are interrelated."

The result of all this research is a robust evolutionary tree. This can be now used to study both the evolution of birds and all the interesting features of our feathered friends that have fascinated scientists and enthusiasts for centuries.

DNA Discovery Center

In April, The Field Museum opened The Daniel F. and Ada L. Rice DNA Discovery Center, which puts a public face on the Pritzker Lab. The center opens up a working state-of-the-art laboratory to Museum visitors, who can observe researchers extracting, sequencing, and analyzing DNA for several projects, including the ongoing work on the Early Bird research project.

The Center has two parts. The exhibition portion presents basic information about DNA; a video about DNA; and interactive displays about Field Museum research. The second part is a working lab. Visitors can watch scientists performing all aspects of their genetic research. At set times during the day, visitors can ask working scientists questions about their research.

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