The circadian cycle of Deep-sea shrimp is based on the tides

Amazing stuff!

"... In the depths of the sea, creatures still sync their internal schedules—but they do it to the tides instead, according to a new study.

Hydrothermal vent ecosystems are full of life that never sees the light of day. Given that most animals examined to date have light-based clocks, researchers wondered if the denizens of the deep have figured out a daily schedule without light—or if they have any clock at all.

So they collected shrimp from a vent, kept them in the dark, and analyzed gene expression patterns every 4 hours for a total of 72 hours. That revealed roughly 12.4-hour cycles instead of the 24-hour ones seen in humans—timing that matches up perfectly with tidal fluctuations. ..."

From the abstract:

"Biological clocks are a ubiquitous feature of all life, enabling the use of natural environmental cycles to track time. Although studies on circadian rhythms have contributed greatly to the knowledge of chronobiology, biological rhythms in dark biospheres such as the deep sea remain poorly understood.

Here, based on a free-running experiment in the laboratory, we reveal potentially endogenous rhythms in the gene expression of the deep-sea hydrothermal vent shrimp Rimicaris leurokolos.

Oscillations with approximately 12 h periods, probably reflecting tidal influence, greatly prevail over others in the temporal transcriptome, indicating R. leurokolos probably depends on a circatidal clock consisting of at least some components independent from the circadian clocks. The tidal transcripts exhibit an antiphased expression pattern divided into two internally synchronized clusters, correlated with wide-ranging biological processes that occur in the nucleus and cytoplasm, respectively.

In addition, the tidal transcripts showed great similarities with genes in fruit flies and mice exhibiting approximately 12 h ultradian rhythms, indicating that the tide probably had a broad impact on the evolution of approximately 12 h oscillations found across the Metazoa. These findings not only provide new insights into the temporal adaptations in deep-sea organisms but also highlight hydrothermal vent organisms as intriguing models for chronobiological studies, particularly those linked to approximately 12 h ultradian rhythms."

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Circatidal control of gene expression in the deep-sea hot vent shrimp Rimicaris leurokolos

Fig. 1 Deep-sea chronobiology study on the hydrothermal vent shrimp Rimicaris leurokolos.