Coastal Animals Have Two Internal Clocks, One for the Sun And One for the Tide

When researchers tamped with sea lice’s internal clocks, the crustaceans were unruffled by the unwinding of their circadian cycles

Arnold Paul

We all have circadian clocks that dictate when we get sleepy, when we wake up, and when jet lag will strike if we travel too far, too fast. Animals that live by the ocean shore, however, turn out to have not one but two inner clocks to contend with: one circadian clock governed by the sun, and another circatidal clock calibrated to the ebb and flow of the tides.

To be fair, the authors of the new study extrapolated this conclusion from studies of just one coastal animal, the tiny speckled sea louse, a crustacean related to rolly pollies that spends its days scampering about the damp sand of intertidal shores. National Geographic explains the louse’s typical day:

E. pulchra forages with the tides, actively swimming when it comes in and then burrowing into the sand when the tide goes out, explained Kyriacou, co-author of a study published September 26 in the journal Current Biology.

It was clear E. pulchra was on a tidal schedule—or running on a circatidal clock—but how that clock worked was up for debate, he said.

To find out, the team turned to what’s known as the “circadian clock gene,” which issues molecular instructions that signal for cells to turn on or off and thus dictate our cycles of sleep and wakefulness, LiveScience explains. The researchers tampered with these proteins in the sea lice, then observed what happened. They exposed another group of sea lice to constant light. The crustaceans, they were surprised to find, continued with their busy foraging, unruffled by neither the environmental nor molecular unwinding of their circadian cycles. This indicates that they operate on independent circadian and circatidal clocks, each of which is cut off from the other process.

Rather than a one-off peculiarity of sea lice, the researchers think the circatidal clock may be a general feature of many tidal creatures. Supporting this hypothesis, researchers from the University of Vienna not connected to the study found similar results in another marine creepy crawler, the bristle worm. “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,” the bristle worm team told LiveScience.

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