How The Moon Controls Biological Cycles

As far as we know, humans are the only living
things that wear watches. But we aren’t the only ones that can tell
time. Earth’s movement sets the rhythms of countless
biological clocks. The 24 hour solar period winds cellular gears
controlling sleep, hunger, and metabolism in creatures ranging from jellyfish to elephants. And our 365-and-a-quarter-day journey around
the sun regulates cycles of seasons, harvests, and migrations. But the phases of our planet’s nearest neighbor
also have a surprising pull on biological rhythms. [OPEN] For many species the moon’s glow is a cue
that’s crucial to their survival. Vampires and emo teenagers aren’t the only
ones who find moonlight romantic. Lots of animals use the 29-and-a-half day
lunar cycle to sync up when it comes to finding a mate. Triggered by the full moon, impalas roar,
which in turn triggers all their female mates to begin ovulation. Using a common signal like this ensures every
member of a species goes looking for a partner at the same time. Lunar cycles are especially important in the
sea. Marine bristle worms live on rocky shorelines,
where they rise to the water’s surface under the dim light of the new moon. The worms mass together, swirling around one
another and release their gametes in sync. This big mating party increases the chances
that any one worm will contribute to the next generation. Some eels also reproduce all at once, and
rely on the dim light of the new moon to avoid predators. The moon also controls the tides, and that
pull can help some animals’ eggs and larvae develop and survive. Fish called grunion lay their eggs high up
on beaches during high tides, where the sand protects the eggs as they develop. They hatch when the next cycle of high tides
washes them out to sea. But what *controls* these living lunar cycles? These species must have an inner moon clock. When scientists raised marine worms in constant
light or darkness, they didn’t try to reproduce. But when they gave them artificial light on
a lunar schedule, the worms did their mesmerizing mating dance. The scientists found special neurons in the
worms’ brains that respond to light, linked to timing genes that control these lunar behaviors. The moon seems to act like a signal that supercharges
the worms’ desire to mate when the light at night is just right. But the moon is more than just a clock. It transforms ecosystems. The full moon is 100 times brighter than the
new moon. This lets animals see their prey, forage,
and navigate better. But all that light can be risky. Many species of frogs avoid calling to their
friends during the full moon, since the extra light makes it more vulnerable to predators. And all the manmade light sources now flooding
the night could provide a fake, full-time full moon that might throw ecosystems out
of whack. So what about us? Women’s reproductive cycles are about the
same length as the lunar cycle, but scientists think that’s probably just a coincidence. If human menstrual cycles were, in fact, linked
to the moon, why not our great ape sisters? Now that millions of women are using apps
to track menstrual periods, it’s become pretty clear there’s likely no connection. So for antelopes, coral, fish, and even wildebeest
on the Serengeti, the phases of life are set by phases up above. Next time you take a look at that fancy clock
in your pocket, remember that you aren’t the only creature on Earth who relies on a
satellite to know what time it is. Stay curious. Yes. Technically speaking, moonlight is just sunlight. So you can stop typing that comment. And no, there’s no such thing as werewol