Why the 'birds and the bees' get sexed up in spring

Melbourne, Jan 30 (ANI): UK researchers have apparently solved a thirty-year puzzle: what makes birds to breed in spring?

The study led by Russell Foster of the University of Oxford wanted to unravel the secret behind how birds knew when it was spring breeding time, reports ABC Online.

After studying how body clocks are regulated by light, Foster, who is a circadian neuroscientist, came to know that the main way birds could know that it is spring is by detecting the changes in the number of daylight hours.

However, experiments in the 1930s showed that birds who had their eyes covered or removed still knew when to breed, according to Foster.

Later experiments implanted fibre optics in birds to simulate a spring-like day and tested the responses of various parts of the brain to this.

"These studies found the birds' reproductive system was triggered to become active when the hypothalamus was illuminated," says Foster.

Although the hypothalamus is deep in the brain's base it can still detect light because light penetrates tissue.

"Huge amounts of light actually reach the base of a brain of a bird and we've measured that empirically," says Foster.

"It's useless of course for any image analysis, but it's perfectly good for telling you whether the light is on or off and therefore how long the day is," the expert added.

The researchers are the first to identify the biochemical basis for this light sensitivity.

They have found a light-sensitive pigment, called VA opsin, in the bird's hypothalamus.

"We now have an understanding at a molecular level of how that light is detected and ultimately how that light signal is being turned into a reproductive response," says Foster.

Foster says VA opsin is absent in all mammals including humans, probably because our ancestors were nocturnal and a photoreceptor buried deep into the brain would not be sensitive enough to detect daylength.

These animals relied on specialised receptors in their eyes rather than in their brains, he says.

The study will be presented at a meeting of the Australian Neuroscience Society being held in Canberra. (ANI)