Is there anything better than a proud and fancy pigeon? (No. The answer is no.) And they’re not just pretty faces; they’re also modern-day scientific stand-ins for their dinosaur ancestors. Scientists interested in the dinosaur-to-bird transition have found that the gene responsible for some pigeons’ feathery feet is better known for creating forelimbs—and in birds, that means wings. The report was published in the journal eLife.
If you’ve never heard of fancy pigeons, well, sit down, because you’re in for a delightful ride. They’re like regular pigeons, except they’re fancy. Okay, there’s more to it than that. People have been breeding pigeons for 500 years, carefully pairing individual birds to create specific body types, feather configurations, and even behavior. The results are surprisingly exotic and often quite beautiful.
But the pigeons you see in the park don’t have feathers on their feet. They’ve got scaly, stereotypically dinosaur-looking legs. So what’s producing the foot floofs (also known as muffs) on their fancier counterparts? Biologist Mike Shapiro and his colleagues decided to find out.
Look at these birds! How are they real?!? Image Credit: Sydney Stringham, University of Utah
They started the old-fashioned way: making pigeon babies. The researchers crossed a floofy Pomeranian pouters with scaly-footed-Scandaroons, and then they crossed their kids to get an additional generation of interbreeding. "In the grandkids, some birds had scaled feet, others had big muffs and others were in between, with a range of scales and feathers," Shapiro said in a press statement. "They usually had both.” To Shapiro and his colleagues, this three-way split suggested that there were only a few genes involved in producing feathered feet.
The researchers then ran a number of DNA sequence tests, looking for any genes that might be connected to foot-feather growth. They found two potential culprits: Tbx5 and Pitx1.
Both genes are associated with fore- and hindlimb growth throughout much of the animal kingdom. "Tbx5 is critical for proper forelimb development in all vertebrates—fish [fins], chickens, mice and even humans," Shapiro said. "Mutations in the gene in humans cause Holt-Oram Syndrome, which results in arm defects and heart defects in newborns."
Pitx1, on the other hand, is responsible for making sure that hind limbs, like legs, grow properly.
The thing is, both genes were found in all the grand-birds, regardless of their foot type. The researchers realized that it wasn’t the genes themselves, but their expression, that might be responsible. A DNA sequence in the floofy-footed birds seems to turn down the volume on Pitx1 and turn up Tbx5, resulting in legs that are feathered and sometimes even structured a bit like forelimbs. They are, Shapiro says, “partially wings.”
So what does this mean for the dinosaurs? What was up with their legs? There's still a lot of work to be done, but this was a pretty good, fancy step in the right direction. (A different team of researchers recently attempted to answer that question by genetically manipulating a chicken so that its leg bones developed to resemble those of dinosaurs.)
"Based on what we found in pigeons, the change from scales to feathers can be genetically very simple," Shapiro says. "This can give us some clues about not only how pigeons get feathered feet, but perhaps about how ancient birds lost foot feathers."