On a summer night in the Bay of Naples, hordes of worms swam upward from the seagrass toward the water’s surface under the light of a waning moon. Not long before, the creatures began a gruesome sexual metamorphosis: Their digestive systems withered, and their swimming muscles grew, while their bodies filled with eggs or sperm. The finger-length creatures, now little more than muscular bags of sex cells, fluttered to the surface in unison and, over a few hours, circled each other in a frantic nuptial dance. They released countless eggs and sperm into the bay — and then the moonlit waltz ended in the worms’ deaths.
The marine bristle worm Platynereis dumerilii gets only one chance to mate, so its final dance had better not be a solo. To ensure that many worms congregate at the same time, the species synchronizes its reproductive timing with the cycles of the moon.
How can an undersea worm tell when the moon is at its brightest? Evolution’s answer is a precise celestial clock wound by a molecule that can sense moonbeams and sync the worms’ reproductive lives to lunar phases.
No one had ever seen how one of these moonlight molecules worked. Recently, however, in a study published in Nature Communications, researchers in Germany determined the different structures that one such protein in bristle worms takes in darkness and in sunlight. They also uncovered biochemical details that help explain how the protein distinguishes between brighter sunbeams and softer moonglow.
It’s the first time that scientists have determined the molecular structure of any protein responsible for syncing a biological clock to the phases of the moon. “I’m not aware of another system that has been looked at with this degree of sophistication,” said the biochemist Brian Crane of Cornell University, who was not involved in the new study.
Such discoveries could be relevant to the physiology of many kinds of creatures, including humans. “We have no other example where we understand these mechanisms in such molecular detail,” said Eva Wolf, a biochemist at the Johannes Gutenberg University of Mainz in Germany who is one of the co-authors of the paper. “These studies help us start to know how moonlight oscillators and synchronization with the moon phases can work.”
Though we wake more often today to the blare of an alarm clock than to the first light of dawn, our bodies still keep time with the sun. In humans, as in many other animals, sophisticated biological timepieces called circadian clocks sync the body’s rhythms to the beats of daybreak and nightfall. Cryptochrome proteins are important pieces of many organisms’ circadian clocks, either sensing light, as in plants, or coordinating with other proteins that do, as in humans.