Circatidal rhythm and the veiled clockwork

• Marine organisms have a tidally-adapted endogenous rhythm, i.e., circatidal rhythm.
• Circatidal rhythm and its underlying mechanism remain poorly investigated in insects.
• Circatidal rhythm could be driven by the circalunidian, circadian, or circatidal clock.
• The circatidal clock is distinct from the circadian clock in one cricket species.

Many intertidal organisms exhibit endogenous rhythms corresponding to the tidal cycle, i.e., circatidal rhythm. However, circatidal rhythm has been poorly investigated in insects. Several hypotheses have been proposed for the clock generating circatidal rhythm. Nevertheless, the physiological mechanisms of the clocks remain unknown, with one of the long-standing questions being whether the circatidal rhythm is generated by circadian clocks, their variations, or clocks distinct from the circadian clock. In the mangrove cricket Apteronemobius asahinai, the circatidal clock operating locomotor activity rhythm differs from the circadian clock at both the molecular and neural level. Dissections of the clock generating the circatidal rhythm are expected in the near future.