Darwin’s short-beak enigma is SOLVED: Scientists discover a gene linked to beak size in pigeons that causes some breeds to develop flat faces 

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  • Mutation in gene called ROR2 linked to beak length in domestic pigeons
  • Gene explains why one species of pigeon has beaks of all shapes and sizes
  • It is also related to Robinow syndrome, a human congenital disorder.

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Scientists have discovered the gene that causes some pigeons to develop flat faces – a puzzle that fascinated the great British naturalist Charles Darwin.

In a new study, academics report that a mutation in a gene, called ROR2, is linked to a reduction in beak size in several breeds of domestic pigeons.

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This ultimately explains why over 350 breeds of domestic pigeons of the same species (Columba livia) have beaks of all shapes and sizes.

The researchers bred two breeds of pigeons—one with a short bill and the other with a long bill—and genetically analyzed their offspring.

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Intriguingly, mutations in ROR2 also underlie a human congenital disorder called Robinow syndrome, the researchers also found.

Old German Owl (left) and Racing Homer (right) – domestic pigeon breeds that researchers bred to study

darwin’s little beak puzzle

Charles Darwin was fond of domestic pigeons. They thought they kept the secrets of selection in their beaks.

Free from the shackles of natural selection, more than 350 breeds of domestic pigeons have beaks of all shapes and sizes within a single species (Columba livia).

The most striking beaks are so small that they sometimes deter parents from feeding their babies.

Centuries of interbreeding taught early pigeons that beak length was controlled only by certain genetic factors.

Yet modern geneticists have so far failed to solve Darwin’s mystery by pinpointing the molecular machinery controlling the small beak.

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The study was led by Elena Boer, who completed research as a postdoctoral fellow at the University of Utah School of Biological Sciences.

“Some of the most striking features of Robinow syndrome are facial features, including a broad, prominent forehead and a short, broad nose and mouth, and are reminiscent of the small-beak phenotype in pigeons,” she said.

‘This makes sense from a developmental standpoint, as we know that the ROR2 signaling pathway plays an important role in vertebrate craniofacial development.’

Charles Darwin was fond of domestic pigeons and raised them in his garden.

He provided important evidence for his theory that changed the world – evolution by natural selection.

Fancy pigeon breeders have created hundreds of varieties that look dramatically different from wild pigeons—but they all come from one species, Columba livia.

The most striking beaks are so small that they sometimes deter parents from feeding their babies.

The Natural History Museum explains: ‘Darwin was fascinated by how a species could be manipulated to such extremes.

‘He used it as an analogy – if breeders can artificially manipulate the way a species looks in captivity, perhaps the environment can manipulate all species naturally in the wild.’

Yet modern geneticists have so far failed to solve Darwin’s mystery by pinpointing the molecular machinery controlling the small beak.

Charles Darwin (pictured) had pigeons, and provided important evidence for his theory that changed the world - evolution by natural selection

Charles Darwin (pictured) had pigeons, and provided important evidence for his theory that changed the world – evolution by natural selection

For the study, researchers bred two pigeons with short and medium beaks—the male was a racing homer, a bird bred for speed with a medium beak with a beak length similar to the ancestral rock pigeon.

The female was an Old German owl, a fancy pigeon breed with a short, squat beak.

Parents with short and medium beaks produced early offspring of children with intermediate length beaks. This brood was named ‘F1’.

When biologists paired the F1 birds with each other, the resulting grandson (‘F2’) had beaks ranging from large to small and all sizes in between.

To measure variation, Boer measured beak size and shape in 145 F2 individuals using micro-CT scans generated at the University of Utah Preclinical Imaging Core Facility.

Boer said, “The cool thing about this method is that it allows us to look at the size and shape of the entire skull, and discover that it’s not just the length of the beak – the braincase size at the same time.” Changes.”

Painted, medium or long beaked pigeon breeds, from left to right - West of England, Cachois, Scandaroon, Show King

Painted, medium or long beaked pigeon breeds, from left to right – West of England, Cachois, Scandaroon, Show King

Pictured, short beaked pigeon breeds, from left to right - English short faced tumbler, African owl, Oriental frill, Budapest tumbler.  All birds with short beaks had the same ROR2 mutation

Pictured, short beaked pigeon breeds, from left to right – English short faced tumbler, African owl, Oriental frill, Budapest tumbler. All birds with short beaks had the same ROR2 mutation

‘These analyzes showed that the variation in beaks within the F2 population was due to actual differences in beak length, and not to variations in overall skull or body size.’

Next, the researchers compared the pigeons’ genomes. First, using a technique called quantitative trait loci (QTL) mapping, they identified DNA sequence variants scattered throughout the genome, and then looked to see if those mutations appeared in the F2 grandkids chromosome.

‘The short-beaked grandparents had the same chromosome fragment as their grandparents with the shorter beak,’ Shapiro said, which told us that the chromosome fragment had something to do with the short beak.

‘And it was on the sex chromosomes that classical genetic experiments suggested, so we got excited.’

High resolution scans of the grandson of Racing Homer and the German Owl Cross. Animation showing the length of the beak from shortest to longest

The team then compared the whole genome sequences of several different pigeon breeds – 56 pigeons of 31 short-billed breeds and 121 pigeons of 58 medium- or long-billed breeds.

The analysis showed that all individuals with short beaks had the same DNA sequence in a region of their genome that contained the ROR2 gene.

‘The fact that we got the same strong signal from two …

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