Discovery reveals why birds get sex on the brain in spring
7 August 2009
Scientists at the University of Oxford and colleagues have identified a gene in the chicken genome that produces a light-sensitive molecule in the hypothalamus region of a bird's brain.
The molecule acts as a light receptor deep in the brains of birds, detecting changes in day length and triggering the seasonal development of the reproductive system.
"When you hear birds singing in the springtime, it's a light-sensitive molecule deep in their brain that's triggered this reproductive event," said Professor Russell Foster from the University of Oxford, who led the study.
"By timing their mating to the changing seasons, birds can make sure that there will be enough food around for their chicks."
Previous research has shown that birds do not use their eyes to measure the increasing number of hours of sunlight, but instead rely on an area deep in the brain. This is possible because bird skulls and brain tissue let a lot of light through.
The molecule identified belongs to a family of photopigments known as the VA opsins, which are not involved in vision but detect slow changes in the light environment such as dawn and dusk.
The researchers showed that when the gene for the pigment is active in nerve cells, the cells generate electric signals in response to light. They also demonstrated that chicken VA opsin is present in the hypothalamus.
"This evidence is as strong as we can get that we've pinpointed the light receptors that tune birds' responses to the changing seasons." said Dr Stephanie Halford, first author on the study.
"We have shown that chickens have a pigment called VA opsin, that it reacts to light, and that it is around in exactly the part of the bird's brain that we know responds to day length."
The research team has also found VA opsins in amphibians, reptiles and other birds, and believe that this deep-brain mechanism may be found in a range of species across all vertebrates apart from mammals.
Image credit: keatl on Flickr
Reference
Halford S et al. VA opsin-based photoreceptors in the hypothalamus of birds. Curr Biol 2009.