Dissociation of Circadian and Circatidal Timekeeping in the Marine Crustacean Eurydice pulchra

Oct 1, 2013Current biology : CB

Separate daily and tidal internal clocks in the marine crustacean Eurydice pulchra

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Abstract

Eurydice pulchra exhibits robust 12.4-hour tidal swimming cycles that are distinct from its 24-hour circadian rhythms.

Tidal swimming cycles are sustained in constant conditions and can be entrained by suitable stimuli.
These tidal rhythms are temperature compensated, indicating they meet criteria for a biological clock.
Pharmacological inhibition of Casein kinase 1 affects both tidal and circadian rhythms, suggesting shared components.
Cloning of circadian genes reveals that manipulations affecting circadian timing do not influence tidal timing.
Findings support the existence of a dedicated circatidal pacemaker separate from the circadian system.

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BACKGROUND: Tidal (12.4 hr) cycles of behavior and physiology adapt intertidal organisms to temporally complex coastal environments, yet their underlying mechanism is unknown. However, the very existence of an independent "circatidal" clock has been disputed, and it has been argued that tidal rhythms arise as a submultiple of a circadian clock, operating in dual oscillators whose outputs are held in antiphase i.e., ~12.4 hr apart.

RESULTS: We demonstrate that the intertidal crustacean Eurydice pulchra (Leach) exhibits robust tidal cycles of swimming in parallel to circadian (24 hr) rhythms in behavioral, physiological and molecular phenotypes. Importantly, ~12.4 hr cycles of swimming are sustained in constant conditions, they can be entrained by suitable stimuli, and they are temperature compensated, thereby meeting the three criteria that define a biological clock. Unexpectedly, tidal rhythms (like circadian rhythms) are sensitive to pharmacological inhibition of Casein kinase 1, suggesting the possibility of shared clock substrates. However, cloning the canonical circadian genes of E. pulchra to provide molecular markers of circadian timing and also reagents to disrupt it by RNAi revealed that environmental and molecular manipulations that confound circadian timing do not affect tidal timing. Thus, competent circadian timing is neither an inevitable nor necessary element of tidal timekeeping.

CONCLUSIONS: We demonstrate that tidal rhythms are driven by a dedicated circatidal pacemaker that is distinct from the circadian system of E. pulchra, thereby resolving a long-standing debate regarding the nature of the circatidal mechanism.

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Dissociation of Circadian and Circatidal Timekeeping in the Marine Crustacean Eurydice pulchra

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