Journal of comparative physiology

, Volume 107, Issue 1, pp 13–37 | Cite as

Plasticity in an isopod's clockworks: Shaking shapes form and affects phase and frequency

  • J. T. Enright


The stimuli which normally synchronize the endogenous tidal rhythm of the isopodExcirolana chiltoni arise from turbulent waves moving across the beach. A phase-response curve for two-h pulses of similar stimuli has been derived from experiments in which individual isopods were treated with vigorous intermittent shaking in a flask of seawater. This response curve differs qualitatively from all results previously obtained by administering pulse stimuli to ordinary circadian rhythms: it is bimodal per circadian cycle, with two intervals of about 6 h duration, during which phase advance of up to 4 h results from treatment, separated by two other 6 h intervals during which phase delay of up to 3 h is evoked. This kind of responsiveness to entraining stimuli is of clear adaptive value for synchronization of a circadian rhythm to the mixed semi-diurnal tidal regime of the isopods' habitat.

In addition to inducing phase shifts, this same treatment can strongly modify the persistent pattern of activity, and such effects also depend upon phase of treatment: when administered shortly before or shortly after onset of activity, shaking tends to increase the amount of activity in subsequent cycles; when administered in antiphase (6 to 18 h after activity onset), it tends to decrease the activity in the dominant activity peak, and to transform a unimodal pattern of activity into a bimodal pattern. Such induction of a persistent secondary peak of activity in a previously unimodal circadian pattern demonstrates a plasticity which has not been previously reported in those circadian rhythms which are synchronized to the day-night cycle.


Beach Circadian Rhythm Phase Advance Activity Onset Similar Stimulus 


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Copyright information

© Springer-Verlag 1976

Authors and Affiliations

  • J. T. Enright
    • 1
  1. 1.Scripps Institution of OceanographyUniversity of CaliforniaLa JollaUSA

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