In a new study, a team led by University of Utah biologists has discovered that different versions of a single gene, called NDP (Norrie Disease Protein), have unexpected links between color patterns in pigeons, and vision defects in humans. These gene variations were likely bred into pigeons by humans from a different pigeon species and are now evolutionarily advantageous in wild populations of feral pigeons living in urban environments.
The U biologists analyzed the genomes of domestic rock pigeons (Columba livia) to determine the mutations that govern the four fundamental color patterns on pigeon wing feathers. They compared the default, ancestral “bar” pattern, named for the horizontal black stripes near the wing tips, against the slightly darker “checker” pattern, the darkest “T-check” pattern, and the lightest “barless” pattern.
They found that a DNA sequence near the NDP gene was very different between bar birds and both T-check and checker birds. In addition, some of the T-check and checker pigeons have more copies of a stretch of DNA near the gene, resulting in even more pigment in their feathers. In all cases, the gene sequence itself is unaltered. In contrast, the least pigmented barless birds had a mutation in the gene sequence itself, which could affect its function.
“That’s pretty wacky. It’s the same gene, but it’s modified in different ways to get completely different results,” said Mike Shapiro, professor of biology at the U and senior author of the paper.
This is the first time NDP has been associated with pigment variation. Pigeon breeders have reported that barless birds have had vision problems for decades. This study discovered that the exact same NDP mutation found in barless pigeons is also found in two human families with hereditary blindness, suggesting that this part of the NDP gene is important in eye development.
Previous research has shown that the darker checker and T-check birds have an advantage in urban environments; they have a longer breeding season and fledge many young out of the nest. The new U study found that the genetic changes associated with checker and T-check patterns probably resulted from humans breeding the domestic rock pigeon with the African speckled pigeon (Columba guinea), a wild pigeon species common in sub-Saharan Africa. A version of the NDP gene was introduced into domestic pigeons several hundred years ago, long after pigeon domestication. The implication is stunning.
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