Bivalve mollusc circadian clock genes can run at tidal frequency

Abstract

Marine coastal habitats are complex cyclic environments as a result of sun and moon interactions. In contrast with the well-known circadian orchestration of the terrestrial animal rhythmicity (approx. 24 h), the mechanism responsible for the circatidal rhythm (approx. 12.4 h) remains largely elusive in marine organisms. We revealed in subtidal field conditions that the oyster Crassostrea gigas exhibits tidal rhythmicity of circadian clock genes and clock-associated genes. A free-running (FR) experiment showed an endogenous circatidal rhythm. In parallel, we showed in the field that oysters' valve behaviour exhibited a strong tidal rhythm combined with a daily rhythm. In the FR experiment, all behavioural rhythms were circatidal, and half of them were also circadian. Our results fuel the debate on endogenous circatidal mechanisms. In contrast with the current hypothesis on the existence of an independent tidal clock, we suggest that a single ‘circadian/circatidal’ clock in bivalves is sufficient to entrain behavioural patterns at tidal and daily frequencies.

Widely rhythmic transcriptome in Calanus finmarchicus during the high Arctic summer solstice period

“…The bimodal aspect of the C. finmarchicus transcriptomes, presenting both daily and ultradian oscillations, as well as a differential daily / ultradian ratio between stations, were in accordance with the bimodal oscillations of circadian clock transcripts (Figure S1, Hü ppe et al, 2020). This corroborated the hypothesis of Hü ppe et al (2020) that the circadian clock could be functional during summer solstice at high latitudes and, as proposed in other species (Enright, 1976;Tran et al, 2020), could be synchronized by both daily and tidal environmental cycles, with a balance between one or the other depending on their relative importance and the associated advantages to synchronize biological processes accordingly, relevant to each ecosystem. Moreover, the station-specific phases of daily and ultradian transcripts compliment the idea of the ability to adapt to site-specific changes of risks and opportunities related to the daily and tidal environmental cycles.…”

Biological rhythms in the deep-sea hydrothermal mussel Bathymodiolus azoricus

“…In the oyster C. gigas, it had been suggested that circatidal rhythms could be generated by a tidally synchronised circadian clock 67 . Recent studies reported tidal expression of circadian clock genes in the laboratory 59 and in the field 68 , supporting the later hypothesis. Understanding the clockwork(s) in marine organisms is complicated by their co-occurrence and interactions.…”

Two light sensors decode moonlight versus sunlight to adjust a plastic circadian/circalunidian clock to moon phase

“…Restricting swarming behaviour to the dark portion of the night might be advantageous to avoid predators that hunt during moonlight. On a mechanistic level we suggest that this PCC clock shares elements with the conventional core circadian oscillator and reveal two highly sensitive light receptors, r-Opsin1 and L-Cry, that are critical to sense and interpret Evidence for plasticity of the conventional circadian clock has started to emerge from other marine systems: Work on the circatidal oscillators of oysters maintained under controlled lab conditions revealed that core circadian clock genes exhibit ~12.4hr cycles under constant darkness, while the transcripts of the same genes cycle with a ~24hr oscillation under light/dark conditions (36). This provides evidence for the ability of the canonical clock to alternate between circadian (~24h) and…”