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Animals Tune Behavior by  Lunar Cycle; but How?

David Coppedge
Photo credit: Ganapathy Kumar via Unsplash.

Tonight’s moon will be full, so here is a timely question. Many unrelated animals tune their behavior by the lunar cycle. How do they do it, given that sunlight overpowers moonlight?

Researchers in Austria think they have found a clue: a cryptochrome protein that appears to respond to the lunar cycle. Cryptochrome proteins are also implicated in the geomagnetic sense in birds. Whatever they found, it surely must represent only a piece of a biological puzzle. Let them explain in this from the University of Wien:

Many marine organisms, including brown algae, fish, corals, turtles and bristle worms, synchronize their behavior and reproduction with the lunar cycle. For some species, such as the bristle worm Platynereiis dumerilii, lab experiments have shown that moonlight exerts its timing function by entraining an inner monthly calendar, also called circalunar clock. Under these laboratory conditions, mimicking the duration of the full moon is sufficient to entrain these circalunar clocks. However, in natural habitats light conditions can vary considerably. Even the regular interplay of sun- and moon creates highly complex patterns. Organisms using the lunar light for their timing thus need to discriminate between specific moon phases and between sun and moonlight. This ability is not well understood. [Emphasis added.]

The first statement should alarm evolutionists. Circalunar clocks are found in very unrelated animals (evolutionarily speaking): vertebrates like fish and turtles and invertebrates like worms and corals. Each of these must have hit upon lunar tuning independently.

The researcher’s paper in Nature Communications points out that we humans have connections to the lunar cycle, too:

In addition, lunar timing effects have also been documented outside the marine environment, and recently uncovered correlations of human sleep and menstrual cycle properties with moon phases have re-initiated the discussion of an impact of the moon even on human biology. As recently documented for corals, desynchronization of these reproductively critical rhythms by anthropogenic impacts poses a threat to species survival.

The Bristle Worm as a Test Case

P. dumerilii, the so-called bristle worm is a polychaete (“much-haired) worm in phylum Annelida. Smithsonian Magazine lists 14 Fun Facts about these polychaetes, an “amazingly diverse family” of marine organisms:

Unbeknownst to most landlubbers, polychaetes rule the seas. There are at least 10,000 species of these swimming bristly worms, some of which pop with brilliant colors or light up with a bioluminescent glow. They’ve adapted to every imaginable marine habitat, from deep hydrothermal vents to crowded coral reefs to the open ocean—and many have found ways to survive that are definitely bizarre.

Interested readers can browse through Smithsonian’s list of facts and look at the pictures. A short horror movie shows a lionfish learning too late not to mess with a bobbit worm (Eunice aphroditois), a different species of bristle worm in the Atlantic. It’s a creature of nightmares, so be forewarned. The poisonous lionfish can’t use its defensive weapons against this lightning-fast monster: a worm! It’s a terrifying creature right out of the movie Tremors. More about bobbit worms can be found at ARCReef.comDo not read this: some bobbit worms grow up to ten feet long! Fortunately, attacks on humans are rare, limited to “nasty bites” (Daily Mail).

Evolutionary Challenges 

Back to P. dumerilii, a much more benign polychaete only 2-4 cm long. A type of ragworm, this species is found worldwide. Wikipedia calls it a living fossil. Although it’s an invertebrate, “it has an axochord, a paired longitudinal muscle that displays striking similarities to the notochord regarding position, developmental origin, and expression profile.” It swims with a coordinated system of cilia on its surface. “Whole-body coordination of ciliary locomotion is performed by a ‘stop-and-go pacemaker system’,” the article says. That’s not the only pacemaker in this amazing little worm. Despite having “a pair of the simplest eyes in the animal kingdom,” it can “see” the phases of the moon. Those little eyes do not help the evolutionary story:

The ciliary photoreceptor cells are located in the deep brain of the larva. They are not shaded by pigment and thus perceive non-directional light. The ciliary photoreceptor cells resemble molecularly and morphologically the rods and cones of the human eye. Additional [sic], they express an ciliary opsin that is more similar to the visual ciliary opsins of vertebrate rods and cones than to the visual rhabdomeric opsins of invertebrates.

The bristle worm’s genome also challenges Darwinism:

The genome of Platynereis dumerilii … contains approximately 1 Gbp (giga base pairs) or 109 base pairs. This genome size is close to the average observed for other animals. However, compared to many classical invertebrate molecular model organisms, this genome size is rather large and therefore it is a challenge to identify gene regulatory elements that can be far away from the corresponding promoter. But it is intron rich unlike those of Drosophila melanogaster and Caenorhabditis elegans and thus closer to vertebrate genomes including the human genome.

Wikipedia prudently abstains from speculating on how these worms evolved.

Possible Lunar Oscillator Found in P. dumerilii

In the introduction to the paper, the authors say, “Despite the importance and widespread occurrence of lunar rhythms, functional mechanistic insight is lacking.” They found a cryptochome protein they call L-Cry that appears to keep time to the full moon. Its asymmetric dimer appears to have two monomers with very different light sensitivities, which “provides the molecular basis to sense and interpret light intensities across five orders of magnitude.” 

This is important because full sunlight swamps moonlight, so the worm brain must be able to discriminate the smaller peaks of illumination from larger ones. Additionally, L-Cry must be able to avoid being tricked by artificial light that can also outshine full moonlight. It must also be robust against darkness on cloudy full-moon nights and by “natural acute light disturbances, such as lightning.” 

Experiments in the “worm room” under controlled simulations of sun and moon illumination cycles demonstrated this ability. “L-Cry’s major role could be that of a gatekeeper controlling which ambient light is interpreted as full-moonlight stimulus for circalunar clock entrainment,” they say. If an organism can set its lunar clock to a full moon, it can also discriminate other lunar phases.

The full moon is unique in having the longest duration of light at night, followed by sunrise. A circalunar clock presupposes, therefore, the ability to measure the duration as well as intensity of light. L-Cry may do this with a ratchet mechanism: as the protein accumulates photons, it reaches higher quantum levels that photoreduce parts of the low-sensitivity monomer. The authors also observed L-Cry accumulating in the nucleus and diminishing in the cytoplasm during the simulated moonlight exposure time. “This suggests that different cellular compartments convey the different light messages to different downstream pathways.”

Even so, this cryptochrome discovery only delivers “the first molecular entry point into the mechanisms underlying a moonlight-entrained monthly oscillator.” The photoreceptor for L-Cry is unknown. Additionally, L-Cry must cooperate with the circadian clock genes, adding to the regulatory complexity. How these proteins signal a cascade of physiological behaviors when it’s time to spawn remains curious. “Certainly, more extensive mechanistic studies are required to further verify our models.”

Convergent Functionality

Finally, an evolutionary consideration: Monthly synchronization by the moon has been documented for a wide range of organisms– including brown and green algae, corals, crustaceans, worms, but also vertebrates… Furthermore, recent reports also provide increasing evidence that the lunar cycle influences human behavior… Are the lunar effects mediated by conserved or different mechanisms?

Since L-Cry is not known in these other species, the authors speculate that either conservation of other proteins will be discovered, or that other proteins with analogous functions will be found. 

Last, but not least the molecular mechanisms underlying the circalunar oscillator also await identification, and it is possible that conservation exists on this level. Examples are known from circadian biology and it will now require further work to reach a similar level of understanding for moon-controlled monthly rhythms and clocks.

Surely, though, conservation of function using entirely different molecular mechanisms poses a severe challenge to Darwinism. It would seem to require entirely different sets of mutations to be selected for a common function. In design theory, intelligence starts with the concept and can use different instruments to play the same tune. 

The Palolo Worm

We end with a spectacular case of circalunar time tuning. Another polychaete, the Palolo Worm of the South Pacific, undergoes a remarkable reproductive cycle timed to both lunar and annual cycles. Britannica explains its life cycle:

The palolo worm of the South Pacific (Palolo siciliensis [P. viridis or Eunice viridis]) inhabits crevices and cavities in coral reefs. As the breeding season approaches, the tail end of the body undergoes a radical change.The muscles and most of the organs degenerate, and the reproductive organs rapidly increase in size. The limbs on the posterior segment become more paddlelike. After the animal backs part way out of its tubelike burrow, the posterior section breaks free and swims to the surface as a separate animal, complete with eyes. The anterior end, still attached to its tube, regenerates a new posterior end. 

The free-swimming half-worms contains sperm and eggs. Tens of thousands of these half-worms swim to the surface as if on cue, and release their reproductive cells always at the same time of year and at a particular phase of the moon.

The free-swimming section always makes its appearance in the early morning for two days during the last quarter of the Moon in October. Twenty-eight days later, it appears in even greater numbers in the final quarter of the November Moon. At the surface of the sea the sperm and eggs are discharged, and fertilization occurs. Palolo tails, considered a delicacy by the Polynesians, are gathered in vast numbers during swarming.

Worms. Such simple, lowly creatures. But what wonders await the biologists who delve into their mechanisms. Like everything else in biology, design-inspired awe explodes in the details.