Journal of comparative physiology

, Volume 77, Issue 2, pp 141–162 | Cite as

A virtuoso isopod

Circa-lunar rhythms and their tidal fine structure
  • J. T. Enright


An extremely elaborate performance, involving endogenous timing with both tidal and lunar frequencies, has been recorded in the locomotor activity of an adult specimen of the intertidal isopod,Excirolana chiltoni. During two months of observation, under constant, non-tidal conditions, this animal showed a persistent tidal rhythm in its swimming activity. Bursts of activity were initially well synchronized with times of tide crest on the shore. The average free-running period of the tidal rhythm was about 24 h 55 min, i.e. about 5 minutes longer than the average period of the tides; thus, the loss of synchrony with the concurrent tides was very gradual. The amount of activity per burst showed a conspicuous pattern of variation, a periodic amplitude modulation which paralleled, in detail, the complex lunar cycle of changes in height of high tide. The free-running period of the bimodal, circa-lunar rhythm of amplitude modulation was one or two days longer than the natural 29-day lunar cycle of tide heights.

Each feature of this recording has been qualitatively replicated in activity records from other individuals of this species. Freshly-collectedExcirolana generally show spontaneous bursts of activity at times of tide crest, bursts which are repeated as a persistent tidal rhythm, the period of which commonly departs by only a few minutes from that of the natural tidal cycle. Superimposed on the tidal rhythm is an endogenous monthly pattern of amplitude modulation, which alters the amount of activity per burst. This circa-lunar rhythm has a free-running period between about 26 and 33 days, and generally leads to maximum activity on days of highest of high tides. The net result of the tidal and lunar rhythms is an activity pattern which permits the isopods to recapitulate, in great detail, certain significant ecological aspects of the mixed, semi-diurnal tidal regime of California.

The experimental data are not compatible with the hypothesis that uncontrolled environmental factors, such as vibrations from waves, were responsible for the rhythmic behavior of the animals. Neither do the data support the hypothesis that “beats” between the observed tidal rhythm and a hidden daily or circadian rhythm were responsible for the observed circa-lunar rhythm. Furthermore, the pattern of the circa-lunar rhythm cannot be accounted for by a single monthly oscillation in the “excitability” of the animals, such as might be mediated by changes in the level of an excitatory or inhibitory hormone in the circulatory system.


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  1. Aschoff, J.: Orcadian activity pattern with two peaks. Ecology47, 657–662 (1966).Google Scholar
  2. Barnwell, F. H.: Daily and tidal patterns of activity in individual fiddler crabs (genusUca) from the Woods Hole region. Biol. Bull.130, 1–17 (1966).Google Scholar
  3. Barnwell, F. H.: The role of rhythmic systems in the adaptation of fiddler crabs to the intertidal zone. Amer. Zool.8, 569–583 (1968).Google Scholar
  4. Bennett, M. F., Shriner, J., Brown, R. A.: Persistent tidal cycles of spontaneous motor activity in the fiddler crab,Uca pugnax. Biol. Bull.112, 267–275 (1957).Google Scholar
  5. Bohn, G.: Sur les mouvements oscillatoires desConvoluta roscoffensis. C. R. Acad. Sci. (Paris)137, 576–578 (1903).Google Scholar
  6. Bünning, E., Müller, D.: Wie messen Organismen lunare Zyklen? Z. Naturforsch.16 b, 391–395 (1961).Google Scholar
  7. Chandrashekaran, M. K.: Persistent tidal and diurnal rhythms of locomotor activity and oxygen consumption inEmerita asiatica (M.-Edw.). Z. vergl. Physiol.50, 137–150 (1965).Google Scholar
  8. Enright, J. T.: The tidal rhythm of activity of a sand-beach amphipod. Z. vergl. Physiol.46, 276–313 (1963).Google Scholar
  9. Enright, J. T.: The search for rhythmicity in biological time series. J. theor. Biol.8, 426–468 (1965a).Google Scholar
  10. Enright, J. T.: Entrainment of a tidal rhythm. Science147, 864–867 (1965b).Google Scholar
  11. Enright, J. T.: Heavy water slows biological timing processes. Z. vergl. Physiol.72, 1–16 (1971a).Google Scholar
  12. Enright, J. T.: The internal clock of drunken isopods. Z. vergl. Physiol.75, 332–346 (1971b).Google Scholar
  13. Gibson, R. N.: Factors affecting the rhythmic activity ofBlennius pholis L. (Tele-ostei). Anim. Behav.19, 336–343 (1971).Google Scholar
  14. Hamner, W. M., Enright, J. T.: Relationships between photoperiodism and circadian rhythms of activity in the house finch. J. exp. Biol.46, 43–61 (1967).Google Scholar
  15. Hauenschild, C.: Lunar periodicity. Cold Spr. Harb. Symp. quant. Biol.25, 491–497 (1960).Google Scholar
  16. Heusner, A. A., Enright, J. T.: Long-term activity recording in small aquatic crustaceans. Science154, 532–533 (1966).Google Scholar
  17. Jones, D. A., Naylor, E.: The swimming rhythm of the sand beach isopodEurydice pulchra. J. exp. mar. Biol. Ecol.4, 189–199 (1970).Google Scholar
  18. Klapow, L. A.: The ecology and behavior of a sand-beach isopod,Excirolana chiltoni: distribution, abundance and temporal pattern in molting, reproduction and swimming activity. PhD thesis, Univ. of Calif, at San Diego, 1971.Google Scholar
  19. Morgan, E.: The activity rhythm of the amphipodCorophium volutator (Pallas) and its possible relationship to changes in hydrostatic pressure associated with the tides. J. Anim. Ecol.34, 731–746 (1965).Google Scholar
  20. Naylor, E.: Tidal and diurnal rhythms of locomotor activity inCarcinus maenas (L.). J. exp. Biol.35, 602–610 (1958).Google Scholar
  21. Neumann, D.: Due lunare und die tägliche Schlüpfperiodik der MückeClunio. Z. vergl. Physiol.53, 1–61 (1966).Google Scholar
  22. Neumann, D.: Die Kombination verschiedener endogener Rhythmen bei der zeitlichen Programmierung von Entwicklung und Verhalten. Oecologia (Berl.)3, 166–183 (1969).Google Scholar
  23. Vielhaben, V.: Zur Deutung des semilunaren Fortpflanzungszyklus vonDictyota dichotoma. Z. Bot.51, 156–173 (1963).Google Scholar

Copyright information

© Springer-Verlag 1972

Authors and Affiliations

  • J. T. Enright
    • 1
    • 2
  1. 1.Scripps Institution of OceanographyUniversity of CaliforniaLa Jolla
  2. 2.Max-Planck-Institut für VerhaltensphysiologieSeewiesen und Erling-AndechsUSA

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