Why are Parrots Green?
The colour of many birds’ plumage is derived from the foods they eat but parrots aren’t like most birds. A recently published study has identified the gene encoding the enzyme which creates yellow pigment in budgerigars. This is important because yellow plus blue makes green plumage. When the yellow gene is switched off, budgies’ plumage becomes blue.
In the wild, budiges are green parrots with yellow faces. The birds proved easy to breed in captivity and have become popular pets. Breeding programmes have led to the development of a variety of plumage colours. This means that breeders have performed extensive studies of inheritance patterns and so possess an excellent knowledge of budgie genetics. Budgies were the perfect bird for scientists to study in order to isolate the yellow gene that enables parrots to be green.
Yellow Pigment in Parrots
This yellow pigment is a "psittacofulvin" which is only found in parrots. Psittacofulvins comprise a group of structurally related pigments that give parrots their stunning variety of brilliant red, orange, and yellow colours. These pigments are both attractive and functional as they mean that feathers are more resistant to degradation by bacteria.
The genetics of plumage colour in budgerigars are relatively well known but the molecular and biochemical aspects of plumage colour remain largely unexplored. Scientists set out to discover precisely which gene governs the yellow trait in parrots and how the resulting enzyme could be switched off.
Budgerigars are the perfect birds for scientists to study in order to develop methodologies for genetic detective work. For example, all blue budgerigars are descendants of a single bird that was born around 130 years ago. All blue budgerigars therefore share the same mutated psittacofulvin gene. This fact allowed researchers to look at the budgerigar genome for regions that were shared only by blue budgies and which differed between wild green budgies and derived budgies. The huge number of potential candidates in the genome could be narrowed down to just eleven.
Half and Half Budgie
One gene in particular looked promising as it was similar to another which encodes an enzyme in yellow fungi. Researchers were given a clue about where this gene was expressed in budgies’ bodies by a bird in a pet shop which had been born half blue and half green with the division straight down the middle of the bird! The budgie, named Twinsy, was the result of twins fusing into one individual early in their development.
The near-perfect symmetry of Twinzy’s blue and green halves suggested that high levels of the yellow psittacofulvin pigment are synthesized locally, in other words, in the feather itself and when it is actively growing. Scientists clearly needed to look for the yellow gene in growing feathers. They were then able to isolate the gene and to identify how the resulting enzyme could be deactivated to switch off the yellow and produce a blue or white budgie.
Other animals possess similar genes and so it is now thought that they play a role beyond dictating pigment colour but further research will be required to establish what that role is.