Portrait of an old German owl, left, and Homer’s race, right. Both domestic pigeons were the ancestors of more than 100 pigeons examined in a study of why domestic pigeons’ beak sizes vary so widely. (Sydney Stringham via University of Utah)
Salt Lake City – There are many animals that intrigued Charles Darwin during his 19th century mythological studies.
It may be most commonly associated with turtles and sparrows, but it often inhabits home pigeons as well. That’s because the species helped shape his theory of natural selection, suggesting that domestic pigeons were artificially selected, Michael Willock wrote in an article titled The Incubator at Rockefeller University in 2013.
But one aspect of the pigeon wondered: Why exactly do the more than 300 different breeds of pigeons have beaks of various shapes and sizes, including beaks so short that it is difficult for parents to feed their young?
More than a century later, researchers at the University of Utah said they now have an answer to what they called “Darwin’s short-beaked riddle.” They say pigeons’ short beaks are the result of a genetic mutation, the same genetic mutation that causes Rubino’s syndrome in humans. Their findings were published Tuesday in the journal Current Biology. “
To arrive at their findings, a team of researchers bred two pigeons with different beaks. Michael Shapiro, James E. Talmage chair of biology at the University of Utah and senior author of the study, explained that home pigeon breeders chose beaks based on aesthetics rather than anything that would benefit the species in nature. For this reason, the researchers knew they could find the genes responsible for different beak sizes.
“One of Darwin’s great arguments is that natural and artificial selection are differences in the same process,” Shapiro said in a statement on Tuesday. “The size of pigeon’s beaks helped figure out how that works.”
The team began breeding Homer’s flights with a medium-sized beak similar to an ancient rock pigeon with an old German owl, a luxurious small-beaked pigeon breed despite the name. The brood was characterized by beaks of medium length. When these birds mated with another, their offspring appeared with different sizes and shapes of the beak.
Elena Boyer — a clinical diversity scientist at ARUP Laboratories, a former postdoctoral researcher at the University of Utah and lead author of the study — then used computed tomography to measure the beaks of more than 100 birds produced as descendants of the original pair of pigeons. She found that not only did the birds’ beaks differ, but they also differed in the shape of the bird’s thinners.
“These analyzes showed that beak diversity within the group is due to actual differences in beak length rather than differences in skull or overall body size,” she said in a statement.
But the paper’s biggest discovery is that their short beaks are the result of changes in the ROR2 gene. This is discovered in two steps.
They initially 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 offspring. Shapiro said the results confirmed what the researchers expected based on previous classic genetic experiments. He said they found that the young grandchildren had “the same piece of the chromosome” as the little beaked grandfather.
Then they analyzed all the genome sequences of the different pigeon strains. This study showed that all small-beaked birds had the same DNA sequence in the genome containing the ROR2 gene. Boyer said finding the same results in two different ways was “really exciting” because it strongly suggests that the ROR2 gene is an important factor in beak size.
She added that ROR2 gene mutations also lead to Rubino’s syndrome in humans.
“Some of the notable features of Rubino’s syndrome are facial features, including a broad and prominent forehead and a short and broad nose and mouth, which are reminiscent of the phenotype of a short beak in pigeons,” she explained. “It makes sense from a developmental standpoint because we know that the ROR2 signaling pathway plays an important role in the development of cranial vertebrates.”
One of Darwin’s many dilemmas regarding animal mutations has now been resolved.
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