There are quite a few gardeners who base their work on the lunar calendar and, for example, sow seeds only during certain phases of the moon. It has not been scientifically proven whether this actually brings better yields in the end. But the followers of this ancient tradition are absolutely convinced of the positive effects.
In any case, it is undisputed that many marine organisms, including brown algae, corals, fish, turtles and annelids, synchronize their reproduction with the lunar cycle. So you must have a sense of the phase of the moon. It does not seem plausible that the animals can perceive tiny differences in the gravitational forces.
But how can the internal calendar of animals recognize the correct phase of the moon? Researchers from the universities of Mainz, Oldenburg and Vienna and the Alfred Wegener Institute in Bremerhaven have investigated this question. In the journal "Nature Communications" they now report that a protein called L-Cryptochrome (L-Cry) has special biochemical properties to distinguish between sunlight and moonlight and even between different phases of the moon.
The researchers were able to show that L-Cry interprets the moonlight and can therefore synchronize their "circalunary clock" in sea annelids. This is important for synchronizing the sexual maturation of the animals, resulting in benefits for the animals' reproduction. Most annelids become sexually mature in the days after the full moon.
So far it has been known from laboratory experiments that the light of the moon is responsible for setting the inner calendar of the annelid species Platynereis dumerilii. In order for this to work, the organisms must be able to distinguish between moonlight and sunlight. What's more, they must even be able to differentiate between the light of a full moon and that of a waxing or waning moon. What enables the animals to do this has so far been an open question.
"We have now discovered that the light-sensitive molecule L-Cry is able to distinguish between different light values," explains Professor Kristin Tessmar-Raible from the Max Perutz Labs at the University of Vienna. This molecule serves the animal as a light sensor that can measure light intensity and duration.
"We have discovered that L-Cry's ability to interpret light correlates with different states of the molecule," adds Professor Eva Wolf of the Institute for Molecular Biology at the University of Mainz. L-Cry contains cofactors, i.e. non-protein components that are essential for its function.
These cofactors – so-called flavin adenine dinucleotides (FAD) – change biochemically under the influence of light. The oxidized FAD, which is adapted to the darkness, changes to a reduced state when exposed to light.
The Mainz scientists could also prove that L-Cry molecules that are exposed to natural moonlight accumulate the very low number of photons for hours, but only at most half of their FADs are reduced. Sunlight, on the other hand, with a number of photons that is more than ten thousand times higher, ensures a rapid reduction in all FADs.
Kristin Tessmar-Raible's team was able to show that the L-Cry molecule changes its position within the cell depending on the type of light it is exposed to. These different localizations apparently lead to different signaling pathways, which then control the physiology and behavior of the annelids.
However, the details of this mechanism are still not understood and are a central topic for future research. This also applies to the question of how the light-induced shift in the location of L-Cry in the cell comes about in the first place.
The researchers suspect that the molecular mechanism they discovered also plays a role in other biological clocks and light-controlled processes.
“We think our discovery goes beyond the monthly timing system. It could be a more general mechanism that helps organisms interpret natural light sources,” says Eva Wolf.
From this she derives the fear that animals could be disturbed by artificial nocturnal light sources in their interpretation of the moonlight.