Mutant gene gives pigeons its head crests

Washington, Feb 1: Scientists have decoded the genetic blueprint of the rock pigeon, revealing secrets about pigeons’ Middle East origins, feral pigeons’ kinship with escaped racing birds and how mutations give pigeons traits like feather head crests.

Michael Shapiro, a biologist at the University of Utah, conducted the research with Jun Wang of China’s BGI-Shenzhen (formerly Beijing Genomics Institute) and other scientists from BGI, the University of Utah, Denmark’s University of Copenhagen and the University of Texas M.D. Anderson Cancer Center in Houston.

“The research identified the genes contributing to variation in the avian head crest, using the domesticated pigeons that so fascinated and inspired Charles Darwin in developing his theory of natural selection,” said George Gilchrist, program director in the National Science Foundation’s (NSF) Division of Environmental Biology, which funded the research.

“This finding illustrates the power of comparative genomics,” he noted.

Key results of this study include sequencing of the genome of the rock pigeon Columba livia, which is among the most common bird species.

Using software developed by paper co-author Mark Yandell, a geneticist at the University of Utah, the scientists revealed that a single mutation in a gene named EphB2 causes head and neck feathers to grow upward instead of downward, creating head crests.

“This same gene in humans has been implicated as a contributor to Alzheimer’s disease, as well as prostate cancer and possibly other cancers,” Shapiro said, noting that more than 80 of the 350 pigeon breeds have head crests, which play a role in attracting mates in many bird species.

The researchers found strong evidence that the EphB2 (Ephrin receptor B2) gene acts as an on-off switch to create a head crest when mutant, and no head crest when normal.

They also showed that the mutation and related changes in nearby DNA are shared by all crested pigeons, so the trait evolved just once and was spread to numerous pigeon breeds by breeders.

Full or partial genetic sequences were analyzed for 69 crested birds from 22 breeds, and 95 uncrested birds from 57 breeds. The biologists found a perfect association between the mutant gene and the presence of head crests.

They also showed that while the head crest trait becomes apparent in juvenile pigeons, the mutant gene affects pigeon embryos by reversing the direction of feather buds-from which feathers later grow-at a molecular level.

Other genetic factors determine what kind of head crest each pigeon develops: shell, peak, mane or hood.

The findings appear in a paper published this week in the online journal Science Express. (ANI)