Circadian clocks, which reset about every 24 hours, are common in organisms living on Earth’s surface. They control sleeping and eating patterns, the rise and fall of body temperature and blood pressure, hormone release and many other important body processes. But the clocks in some animals tick-tock to a different beat.
Lunar clockAlong with its circadian clock, a marine worm called Platynereis dumerilii has a timer set to the moon, which controls when the animals spawn. No one has discovered yet which protein gears drive this lunar clock. But experiments have demonstrated that the lunar clockworks are different from those that keep the animal’s circadian clock ticking.
The speckled sea louse Eurydice pulchra follows tidal rhythms so it knows when to burrow deep into the sand to avoid being swept out to sea and when to emerge to forage. The tidal clock is paced by a protein called casein kinase 1, which may be a gear left from an ancient clock upon which all others have been built. (See “The origin of biological clocks.”) Antioxidants called peroxiredoxins also follow the tidal rhythm set by that protein, scientists reported in April in Current Biology.
Prolonged clocksSomalian cave fish, Phreatichthys andruzzii, haven’t seen the sun in more than a million years, but they still have the gears of standard circadian clocks. This clock no longer responds to light. It has wound down and now ticks out a 47-hour cycle, perhaps to synch with cyclical changes in the caves happening on that time scale. Or maybe the clock is slowly breaking because it no longer gives the fish an advantage.
Some cicadas follow even longer clocks, emerging from under ground every 13 to 17 years. No one knows how the insects mark time, says chronobiologist Barbara Helm of the University of Glasgow. Experiments suggest that animals don’t just count days ticked off by their circadian clocks, she says. That could mean that organisms have other timers that keep track of longer time spans, such as years.