Bird DNA leads to strange family tree

Birds of a feather may flock together, but their appearances can be deceiving. Birds that look similar may not be as closely related as field guides might suggest. That’s the conclusion of a new study. When researchers grouped birds by DNA, rather than looks, they turned up some surprising family members.

Falcons, for example, hunt small animals. But the new study finds these birds are more closely related to parrots than to hawks, eagles and other birds of prey. Another surprise: flamingos. The closest cousin of these brightly colored waterbirds is the grebe, a diving bird that looks like a duck. In fact, flamingos and grebes occupy a lonely branch on the family tree. And both of these birds are more closely related to pigeons than to any other waterbird, the study concludes.

It’s not uncommon for birds that look or behave differently to in fact be closely related, says Erich Jarvis. This neuroscientist at Duke University in Durham, N.C., helped lead the new research. And, he points out, bird species with different ancestors may develop similar looks and behaviors. This can happen when animals, over many generations, adapt to similar lifestyles.

He says some bird-lovers may be surprised by the findings, which were published December 12 in Science. Others might read it and nod in agreement.

“Because there were so many different views out there, some people said, ‘Ah, you confirmed what I said a long time ago,’” Jarvis told Science News. “Others were just torn apart.”

A tree of life uses a branched, treelike diagram to depict how organisms relate to one another. Species change slowly over time, through a process known as evolution. On a tree of life, the outer, twiglike, branches represent species alive today. Follow those smaller twigs to where they branch off from thicker limbs and you find the ancestors of today’s species.

Early trees of life grouped birds together by similarities — or differences — in their bones and body parts. More recently, scientists have begun focusing on the animals’ DNA. Jarvis and the scientists he worked with looked at this DNA in a big way.

Inside almost every cell of an organism is information that is passed from parents to their offspring. This information is “written” using a molecule called DNA. It instructs cells on how to grow and function. When a species evolves, its DNA changes.

In earlier efforts to use DNA to build a tree of life, scientists studied certain fragments of DNA. But Jarvis and his coworkers studied changes in all of the DNA they could get out of a bird to identify connections among 48 separate bird species.

Figuring out who is truly related to whom in modern bird families has been an ongoing problem, says Shannon Hackett. A biologist at the Field Museum in Chicago, she did not work on the new study. Part of the problem, she explains, is that at some point in the distant past, there was an explosion in the number of bird species. This rapid increase has made it difficult for scientists to decode the history of birds from fossils.

In 2008, Hackett’s team studied 19 different segments of DNA from 169 bird species. Their tree of life suggested that falcons and hawks, and grebes and ducks, were only distantly related. Those surprises were confirmed by the new study. Jarvis and his team used cutting-edge technology and much more genetic data to get an even clearer picture of bird DNA.

This new tree of life may help scientists gain confidence in controversial ideas about bird evolution, says biologist Sushma Reddy of Loyola University Chicago. She worked on a 2008 study with Hackett, but not on the new tree.

The next step is to fill in the missing branches and twigs, Hackett told Science News. “There are more than 10,000 species of birds,” she says, “and the tree has [only] 48 of them.”

Power Words

behavior  The way a person or other organism acts towards others, or conducts itself.

cell   The smallest structural and functional unit of an organism. Typically too small to see with the naked eye, it consists of watery fluid surrounded by a membrane or wall. Animals are made of anywhere from thousands to trillions of cells, depending on their size.

DNA   (short for deoxyribonucleic acid) A long, double-stranded and spiral-shaped molecule inside most living cells that carries genetic instructions. In all living things, from plants and animals to microbes, these instructions tell cells which molecules to make.

evolution   A process by which species undergo changes over time, usually through genetic variation and natural selection. These changes usually result in a new type of organism better suited for its environment than the earlier type. The newer type is not necessarily more “advanced,” just better adapted to the conditions in which it developed.

evolutionary biologist   Someone who studies the adaptive processes that have led to the diversity of life on Earth. These scientists can study many different subjects, including the microbiology and genetics of living organisms, how species change to adapt, and the fossil record (to assess how various ancient species are related to each other and to modern-day relatives).

evolve   To change gradually over generations, or a long period of time. In living organisms, the evolution usually involves random changes to genes that will then be passed along to an individual’s offspring. These can lead to new traits, such as altered coloration, new susceptibility to disease or protection from it, or different shaped features (such as legs, antennae, toes or internal organs). Nonliving things may also be described as evolving if they change over time. For instance, the miniaturization of computers is sometimes described as these devices evolving to smaller, more complex devices.

fossil   Any preserved remains or traces of ancient life. There are many different types of fossils: The bones and other body parts of dinosaurs are called “body fossils.” Things like footprints are called “trace fossils.” Even specimens of dinosaur poop are fossils. The process of forming fossils is called fossilization.

gene   (adj. genetic) A segment of DNA that codes, or holds instructions, for producing a protein. Offspring inherit genes from their parents. Genes influence how an organism looks and behaves.

generation  A group of individuals born about the same time or that are regarded as a single group. Your parents belong to one generation of your family, for example, and your grandparents to another. Similarly, you and everyone within a few years of your age across the planet -are referred to as belonging to a particular generation of humans.

genetic  Having to do with chromosomes, DNA and the genes contained within DNA. The field of science dealing with these biological instructions is known as genetics. People who work in this field are geneticists.

neuroscience  Science that deals with the structure or function of the brain and other parts of the nervous system. Researchers in this field are known as neuroscientists.

prey Animal species eaten by others.

species  A group of similar organisms capable of producing offspring that can survive and reproduce.

tree of life    A diagram that uses a branched, treelike structure to show how organisms relate to one another. Outer, twiglike, branches represent species alive today. Ancestors of today’s species will lie on thicker limbs, ones closer to the trunk.