Plankton Get Jet Lagged Too?

A hormone that governs sleep and jet lag in humans may also drive the mass migration of plankton in the ocean, according to a new study.

The hormone in question, melatonin, is not only essential to maintaining our daily rhythm, but European scientists have also found that it governs the nightly migration of a plankton species from the surface to deeper waters. Published in the journal Cell, the findings indicate that melatonin's modern role in controlling daily rhythms in humans probably evolved early in the history of animals.

When melatonin patterns get thrown out of whack, that's when humans experience what we know as jet lag, often the symptom of a long flight crossing into a different time zone. But virtually all animals, including the marine ragworm Platynereis dumerilii, have melatonin.

This worm's larvae take part in what has been described as the planet's biggest migration. Using microscopic hairs called cilia, they migrate to the sea surface at dusk, and then throughout the night they settle back down to deeper waters to take shelter from harmful UV rays.

"We found that a group of multitasking cells in the brains of these larvae that sense light also run an internal clock and make melatonin at night," lead researcher Detlev Arendt said in a statement. "So we think that melatonin is the message these cells produce at night to regulate the activity of other neurons that ultimately drive day-night rhythmic behavior."

Scientists at the European Molecular Biology Laboratory (EMBL) in Germany confirmed this suspicion using modern molecular sensors, which allowed them to visualize the activity of these neurons in the larva's brain, and found that it changes radically from day to night. This drives the motion of the worms' cilia, allowing them to sink and float in time with the daylight.

The findings, researchers say, suggest that the cells that control our rhythms of sleep and wakefulness may have first evolved in the ocean, hundreds of millions of years ago, in response to pressure to move away from the Sun.