Natures wonders: synchronized by the light of the moon (Introduction)

by David Turell , Sunday, February 26, 2023, 17:21 (634 days ago) @ David Turell

Ocean organisms act in this way:

https://knowablemagazine.org/article/living-world/2023/lunar-cycles-guide-spawning?utm_...

"coral releasing a colorful bundle of eggs and sperm, tightly packed together. “You’re looking at it and it starts to flow to the surface,” Shlesinger says. “Then you raise your head, and you turn around, and you realize: All the colonies from the same species are doing it just now.”

"Some coral species release bundles of a pinkish- purplish color, others release ones that are yellow, green, white or various other hues. “It’s quite a nice, aesthetic sensation,” says Shlesinger, a marine ecologist at Tel Aviv University, Israel, who has witnessed the show during many years of diving. Corals usually spawn in the evening and night within a tight time window of 10 minutes to half an hour. “The timing is so precise, you can set your clock by the time it happens,” Shlesinger says.

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"How does it work? That has long been a mystery, but researchers are getting closer to understanding. They have known for at least 15 years that corals, like many other species, contain light-sensitive proteins called cryptochromes, and have recently reported that in the stony coral, Dipsastraea speciosa, a period of darkness between sunset and moonrise appears key for triggering spawning some days later.

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"The bristle worm originally comes from the Bay of Naples but has been reared in laboratories since the 1950s. It is particularly well-suited for such studies, says Kristin Tessmar-Raible, a chronobiologist at the University of Vienna. During its reproductive season, it spawns for a few days after the full moon: The adult worms rise en masse to the water surface at a dark hour, engage in a nuptial dance and release their gametes. After reproduction, the worms burst and die.

"The tools the creatures need for such precision timing — down to days of the month, and then down to hours of the day — are akin to what we’d need to arrange a meeting, says Tessmar-Raible. “We integrate different types of timing systems: a watch, a calendar,” she says. In the worm’s case, the requisite timing systems are a daily — or circadian — clock along with another, circalunar clock for its monthly reckoning.

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"Though the story is far from complete, the scientists have evidence that the protein plays a key role in something very important: distinguishing sunlight from moonlight. L-Cry is, in effect, “a natural light interpreter,” Tessmar-Raible and coauthors write

"The role is a crucial one, because in order to synchronize and spawn on the same night, the creatures need to be able to stay in step with the patterns of the moon on its roughly 29.5-day cycle — from full moon, when the moonlight is bright and lasts all night long, to the dimmer, shorter-duration illuminations as the moon waxes and wanes.

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"How does the worm know that it’s sensing moonlight, though, and not sunlight? Under moonlight conditions, only one of the two flavins was photoreduced, the scientists found. In bright light, by contrast, both flavin molecules were photoreduced, and very quickly. Furthermore, these two types of L-Cry ended up in different parts of the worm’s cells: the fully photoreduced protein in the cytoplasm, where it was quickly destroyed, and the partly photoreduced L-Cry proteins in the nucleus.

"All in all, the situation is akin to having “a highly sensitive ‘low light sensor’ for moonlight detection with a much less sensitive ‘high light sensor’ for sunlight detection,” the authors conclude in a report published in 2022.

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"...they confirmed that another molecule is key for the worm to spawn during the right one- to two-hour window — the dark portion of that night between sunset and moonrise — on the designated spawning nights.

"Called r-Opsin, the molecule is extremely sensitive to light, the scientists found — about a hundred times more than the melanopsin found in the average human eye. It modifies the worm’s daily clock by acting as a moonrise sensor, the researchers propose (the moon rises successively later each night). The notion is that combining the signal from the r-Opsin sensor with the information from the L-Cry on what kind of light it is allows the worm to pick just the right time on the spawning night to rise to the surface and release its gametes.

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"Scientists are also interested in knowing what roles are played by microbes that might live with marine creatures. Corals like Acropora, for example, often have algae living symbiotically within their cells. “We know that algae like that also have circadian rhythms,” Tarrant says. “So when you have a coral and an alga together, it’s complicated to know how that works.'”

Comment: an amazingly precise reaction to the moon's schedule. Why is this required? Or was it designed?