12 November 2020

Giant study reveals the evolution of birds from dinosaurs to present day


Researchers from University of Copenhagen and partner institutions are in the midst of mapping the genetic material of all birds. Amongst many other things, their data provides an opportunity to investigate which birds descended from dinosaurs first, how wings developed and why songbirds sing as they do.

Photo of a dinosaur and a parrot
Photo: Getty Images

How have the genomes of birds developed since their evolution from dinosaurs to birds? Which genes are lost and which gained? And what consequences does it have for the way birds look, sing and behave?

These questions can now be answered by analyzing the data in one of the world’s largest genome-sequencing projects on animals – the B10K – where researchers are mapping the genomes of each of the world’s 10,500 bird species.

Up until now, researchers from University of Copenhagen and partner institutions have mapped 363 genomes from 92.4 percent of all bird families on Earth.

In their new study, the second phase out of four, they have investigated the genomic differences and similarities in the birds, and can confirm that their genetic material is remarkably similar.

"We are surprised by the similarities among avian DNA. Also, birds have lost numerous genes in their common ancestor since their evolution from dinosaurs during the last more than 150 million years. This is a result of their adaptation towards being able to fly" explains Professor Guojie Zhang, of the University of Copenhagen’s Department of Biology and one of B10K’s lead researchers.

Collage of birds emerging in different parts of the world, by Josefin Stiller
Collage of birds emerging in different parts of the world, by Josefin Stiller

By losing a gene, the beautiful voices of songbirds have emerged

Genes were also lost and gained in more recent bird evolution, for example in the songbirds, which are a part of the passerine bird family - an extraordinary diverse bird group with over 6000 species.

According to the study, songbirds have lost a gene known as cornulin, which controls mechanical resilience and elasticity of the esophagus and affects their ability to sing.

The loss of this gene has permitted the oesophagus to become more flexible, allowing songbirds to use the mouth and oesophagus as an acoustic filter. By rapidly changing the volume of this cavity, overtones (upper harmonics) are eliminated and pure tones of different frequencies are produced.

The ability to sing with pure tones is a special feature of songbirds, according to Leopold Eckhart who is a professor at the Medical University of Vienna and a researcher on the B10K.

“Most birds communicate through sounds but songbirds are outstanding. Surprisingly, it was not the evolution of new genes but the loss of an old gene that helped songbirds to become the best singers,” he says.

Most birds, reptiles and mammals, including humans have retained cornulin, whereas songbirds benefited from mutations that destroyed this gene. Researchers are now using the new bird genome sequences to identify more subtle changes in other genes that also contributed to the evolution of birdsong, Eckhart explains.  

It is important to note that this is just one of many examples on how the bird genomes are different from each other.

Meadow Swallow singing. Photo: Getty Images
Meadow Swallow singing. Photo: Getty Images

Tissue samples could shed light on avian evolution

The researchers in the B10K study collected tissue samples from birds in the Danish Natural History Museum, the Smithsonian National Museum of Natural History and Louisiana State University’s Museum of Natural Science to name a few.

The genomes from the tissue samples were analyzed using computer models that compare genomes to identify differences and similarities. With this method, the researchers were able to reveal hidden parts of their evolution.

"Genomes are a rich source of information that can be applied to a range of questions. We are using the data to reconstruct the evolutionary relationships among different birds and to uncover the differences and similarities in certain genes and pathways. The genomes also facilitate analyses typically done in conservation genetics that aim to preserve the viability of bird populations," concludes Josefin Stiller, a postdoc at the Department of Biology and one of the researchers taking part in the extensive mapping project.