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.