US researchers say they have solved Darwin’s pigeon riddle

SALT LAKE CITY – Many animals sparked the interest of Charles Darwin during his legendary studies in the 19th century.

It can be mainly associated with turtles and finches, but it has also often lingered on the domestic pigeon. This is because the species helped shape his theory of natural selection, as he noted that domestic pigeons were artificially selected, Michael Wheelock wrote in an article for Rockefeller University’s “The Incubator” in 2013. .

But one facet of pigeons he wondered about was why, exactly, the more than 300 different breeds of pigeons had beaks of different shapes and sizes, including beaks short enough to make it difficult for parents to feed their young. ?

More than a century later, researchers at the University of Utah say they now have an answer to what they have called “Darwin’s short-nosed riddle.” They say the short bills in pigeons are the result of a genetic mutation, the same genetic mutation that causes Robinow syndrome in humans. Their findings were published Tuesday in the journal “Current Biology”.

To reach their conclusion, a team of researchers bred two pigeons with different bills. Michael Shapiro, University of Utah James E. Talmage Presidential Chair in Biology and lead author of the study, explained that domestic pigeon breeders select beaks based on aesthetics, not anything that would benefit the species in the wild. Because of this, the researchers knew they could find genes responsible for different beak sizes.

“One of Darwin’s big arguments was that natural selection and artificial selection are variants of the same process,” Shapiro said in a statement Tuesday. “The size of the pigeon’s beak was instrumental in understanding how it works.”

The team started out by breeding a Racing Homer with a medium sized bill similar to the ancestral rock pigeon with an Old German Owl, which despite its name is a fancy breed of pigeon with a small bill. Their brood had beaks of intermediate length; when these birds mated with one another, their offspring exhibited different sizes and shapes of beaks.

Elena Boer – a clinical variant scientist at ARUP Laboratories, a former postdoctoral researcher at the University of Utah and lead author of the study – then used micro-scanners to measure the beaks of more than 100 birds produced as grandchildren of the original pigeon pair. She found that not only the beaks differed, but also the shape of the birds’ skulls.

“These analyzes demonstrated that the variation in the beak within the population (of grandchildren) was due to actual differences in beak length and not to a variation in the overall size of the skull or body,” t -she declared in a press release.

But the paper’s biggest finding is that the short beaks are the result of alterations in the MMR2 gene. This was discovered in two stages.

They first used a process called quantitative trait loci mapping, which helped them identify DNA sequence variants and also the ability to look for mutations in the chromosomes of grandchildren. The results confirmed what the researchers expected based on previous classic genetic experiments, according to Shapiro. He said they discovered that grandchildren with a small beak had “the same piece of chromosome” as the grandparent with a small beak. “

They then analyzed all the genome sequences of the different breeds of pigeons. This research showed that all birds with small beaks have the same DNA sequence in the genome that contains the MMR2 gene. Boer said that finding the same results in two different approaches was “really exciting” because it strongly indicates that the ROR2 gene is the main factor in beak size.

She added that mutations in the ROR2 gene also lead to Robinow syndrome in humans.

“Some of the most striking features of Robinow syndrome are the facial features, which include a broad, prominent forehead and a short, wide nose and mouth, and are reminiscent of the short-billed phenotype in pigeons,” he said. she explains. “This makes sense from a developmental perspective because we know that the ROR2 signaling pathway plays an important role in craniofacial development in vertebrates.”

And one of Darwin’s many dilemmas regarding animal mutations has now been resolved.

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