The curious genetics of pigeon patterns
Pale pigeons with poor vision share a similar mutation to that found in humans with some forms of hereditary blindness.
The rock pigeon is a familiar sight in urban settings all over the world. Domesticated thousands of years ago and still raised by hobbyists, there are now more than 350 breeds of pigeon. These breeds have a spectacular variation in anatomy, feather color and behavior. Color patterns are important for birds in species recognition, mate choice and camouflage. Pigeon fanciers have long observed that color patterns can be linked to health problems, such as lighter birds suffering more often from poor vision.
In addition, pigeons with certain pigment patterns are more likely to survive and reproduce in urban habitats. But despite centuries of pigeon-breeding and the abundance of rock pigeons in urban spaces, how pigeons generate such different feather color patterns, is still largely a mystery.
Vickrey et al. sequenced the genomes of pigeons with different patterns and found that a gene called NDP played an important role in wing pigmentation. In birds with darker patterns (called checker and T-check) the gene NDP was expressed more in their feathers, but the gene itself was not altered. The lightest colored birds (barless patterned), however, had a mutation in the NDP gene itself that led to less pigmentation.
The NDP mutation found in barless pigeons is the same as one that is sometimes found in the human version of NDP, where it is linked to hereditary blindness. Vickrey et al. also discovered that the darker patterns most likely arose from breeding of the rock pigeon with a different species, the African speckled pigeon, something pigeon fanciers have suspected for some time.
The findings could help to parse out the different functions of the NDP gene in both pigeons and humans. Mutations in the NDP gene in humans typically cause a range of neurological problems in addition to loss of sight, but in barless pigeons, the mutation appears to cause only vision defects. These findings suggest that a specific part of the gene is particularly important for vision in birds and humans, and shed light on the surprisingly complex evolutionary history of the rock pigeon.
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