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The biggest sex event on Earth

Every year, and shortly after a full moon, billions of corals across a third of a million square kilometers of Australia's Great Barrier Reef enter in a frenzy of reproduction. Now, an international team of Australian and Israeli researchers has discovered the key to this moonlight romance. It is an ancient light-sensitive gene, known as a cryptochrome, which is present not only in corals, but in insects, fish and mammals -- including humans. These genes are primitive light-sensing pigment mechanisms which predate the evolution of eyes -- and are pretty sensitive to blue light.

It's probably not what you think. Every year, and shortly after a full moon, billions of corals across a third of a million square kilometers of Australia's Great Barrier Reef enter in a frenzy of reproduction. Now, an international team of Australian and Israeli researchers has discovered the key to this moonlight romance. It is an ancient light-sensitive gene, known as a cryptochrome, which is present not only in corals, but in insects, fish and mammals -- including humans. These genes are primitive light-sensing pigment mechanisms which predate the evolution of eyes -- and are pretty sensitive to blue light.

Corals moonlight romance (image 1)

But let's start with some pictures. The image above shows some corals Acropora millepora. These corals "spawn on one of a couple of nights each year. Biologists now track this synchronized ability to the presence of ancient cryptochromes molecules that are triggered by blue light." (Credit: Jez Roff, Centre for Marine Studies, The University of Queensland) Here are two links to a larger version of this picture and to another spectacular one.

Corals moonlight romance (image 2)

This picture above shows how "corals of the same species synchronise their spawning to within the same hour." (Credit: ARC Centre of Excellence for Coral Reef Studies) You'll find a larger version of this picture in this mini photo gallery (3 images).

Now, before looking at the scientific details, here is how The New York Times starts its report about this discovery in "Sexy Corals Keep 'Eye' on Moon, Scientists Say" (Free registration required). "Birds do it. Bees do it. Even lowly corals do it -- but infrequently, forgoing sex for as long as a year. Then, at night, just after the full moon, under warm tropic breezes, the corals dissolve in an orgy of reproduction, sowing waters with trillions of eggs and sperm that swirl and dance and merge to form new life. The frenzy can leave pink flotsam. Scientists discovered the mysterious rite of procreation in 1981 and ever since have puzzled over its details. The moon clearly rules the synchronized mass spawning, which happens during different months in different parts of the globe, but usually in the summer. But how do corals monitor the moon's phases and know when to start mingling?

The answer has been given by Oren Levy of the ARC Centre of Excellence for Coral Reef Studies (CoECRS) and the University of Queensland, where he is a visiting scholar under the supervision of professor Ove Hoegh-Guldberg.

About this discovery, Hoegh-Guldberg said, "This is the key to one of the central mysteries of coral reefs. We have always wondered how corals without eyes can detect moonlight and get the precise hour of the right couple of days each year to spawn." Levy added that "the remarkable synchronisation of spawning occurring all along the Reef immediately following a full moon suggested that moonlight was a key factor."

This led him to his discovery. "Exposing corals to different colours and intensities of light and sampling live corals on reefs around the time of the full moon, Dr Levy found the Cry2 gene at its most active in Acropora corals during full moon nights. 'We think these genes developed in primitive life forms in the Precambrian, more than 500 million years ago, as a way of sensing light,' he explains. 'The fact they are linked with the system that repairs damage from ultraviolet (UV) radiation suggests they may evolved in eyeless creatures which needed to avoid high daytime UV by living deep in the water, but still needed to sense the blue light shed by the moon to synchronise their body clocks and breeding cycles.'"

For more information, this research work has been published in Science under the name "Light-Responsive Cryptochromes from a Simple Multicellular Animal, the Coral Acropora millepora" (Volume 318, Number 5849, Pages 467-470, October 19, 2007). Here is the beginning of the abstract. "Hundreds of species of reef-building corals spawn synchronously over a few nights each year, and moonlight regulates this spawning event. However, the molecular elements underpinning the detection of moonlight remain unknown. Here we report the presence of an ancient family of blue-light–sensing photoreceptors, cryptochromes, in the reef-building coral Acropora millepora."

Sources: ARC Centre of Excellence for Coral Reef Studies, October 19, 2007; William J. Broad, The New York Times, October 19, 2007; and various websites

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