Some Marine Animals have Multiple Internal Clocks

The body's internal clock, also known as the circadian rhythm, helps us set our schedule. But two new research papers presented in the journals Current Biology and Cell Reports suggests that animals living in marine environments keep to their schedules with the help of multiple -- and in some cases interacting -- internal tidal clocks.

"The discovery of the circadian clock mechanisms in various terrestrial species from fungi to humans was a major breakthrough for biology," said Charalambos Kyriacou of the University of Leicester, who led one of the two studies on an inter-tidal crustacean known as a speckled sea louse. "The identification of the tidal clock as a largely separate mechanism now presents us with an exciting new perspective on how coastal organisms define biological time."

The second study highlighted interactions between the marine bristle worm's familiar 24-hour circadian clock and its internal circalunar clock.

"Our results suggest that the bristle worm possesses independent, endogenous monthly and daily body clocks that interact," said Kristin Tessmar-Raible from University of Vienna. "Taking this together with previous and other recent reports, evidence accumulates that such a multiple-clock situation might be the rule rather than the exception in the animal kingdom."

In Kyriacou's study, the scientists observed that if the 24-hour circadian clock of the sea louse is disrupted, the creature's 12.4-hour tidal clock keeps on ticking.

"The surprise was to discover just how hard-wired, robust, and independent the tidal clock is in these animals; it keeps working no matter what we throw at its circadian clock," Kyriacou said.

In Tessmar-Raible's study, the researcher team showed that the moon-driven clocks of bristle worms, which provide the animals with an "intrinsic month," went on to function even when the researchers disrupted the animals' circadian clocks. But the researchers also learned that the two clock mechanisms interact. The length and strength of the bristle worm's circadian rhythm adjust according to the circalunar clock.

"This means that there might be a whole level of regulation on the molecular and behavioral level for which we have just scratched the surface," Tessmar-Raible said.