for National Geographic News
Australian and Israeli scientists have discovered the trigger for the planet's biggest group sex spectacle: the mass spawning of hard corals along Australia's Great Barrier Reef.
One week each year in spring, after a full moon, millions of corals release eggs and sperm in what Bill Leggat, a co-author of the new study, called "a slow symphony."
But until now how the primitive animals—which lack brains or eyes—synchronized the mass spawning was a mystery.
In today's issue of the journal Science, researchers reveal that they have isolated an ancient gene in the corals' DNA that can detect moonlight.
By exposing corals to different colors and intensities of light, the team found that the gene—known as Cry2—was most active in Acropora corals during a full moon.
Leggat, a lecturer at James Cook University in Cairns, Australia, said Cry2 encodes a type of protein known as a cryptochrome, which appears to trigger the corals' reproductive cycle.
"This particular gene allows the coral to sense blue light and to actually work out what phase the moon is in," he added.
The research also suggests that the basic ability to sense changes in light and adapt a 24-hour cycle appeared early in the evolution of animals.
Cry2 prompts a series of biochemical reactions that is surprisingly sophisticated, Leggat said.
Some 400 or 500 species of corals all spawn simultaneously during the week, creating vast slicks across the ocean, he pointed out.
"It's just magical," Leggat said. "To just sit in front of an individual coral and watch the pink sperm bundles get slowly pushed out of the corals' mouth and float away—it's incredible to watch."
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