Resetting a circalunar reproduction rhythm with artificial moonlight signals: Phase-response curve and ‘moon-off’ effect
‘Moonlight’ applied continuously every night does not affect the period of the freerunning rhythm (31 days at 20° C).
Two series of pulse experiments were conducted: In the first series, worms (otherwise kept with absolutely dark nights) were perturbed at various circalunar phases by a complex signal consisting of ‘moonlight’ on four successive nights. In the second series, worms (previously kept with constantly ‘moonlit’ nights) were pulsed with simple ‘moon-off’ signals. Both types of experiment resulted in a phase-response curve (pulse-induced phase shifts as function of circalunar phase) that shows the general properties of circadian response curves. Phase shifts (advances and delays) caused by the complex 4-day ‘moonlight’ signals were equal to those effected by simple ‘moon-off’ stimuli given at circalunar phases coinciding with the ends of the complex pulses.
It is concluded that the decisive resetting signal for entrainment to a ‘moonlight’ cycle is afforded by the transition from ‘moonlit’ to dark nights (discrete entrainment by ‘moon-off’). The phase-response curves strongly support the idea that the circalunar timing system displays an essentially oscillating nature. The curves allow prediction of the observed phase relation between the entrained reproduction rhythm and the zeitgeber cycle.
The significance of the results for interpreting entrainment under natural conditions in a field population is discussed.
- Aschoff J (1965) Response curves in circadian periodicity. In: Aschoff J (ed) Circadian clocks. North-Holland, Amsterdam, pp 95–111Google Scholar
- Enright JT (1965) Synchronization and ranges of entrainment. In: Aschoff J (ed) Circadian clocks. North-Holland, Amsterdam, pp 112–124Google Scholar
- Enright JT (1976) Plasticity in an isopod's clockworks: Shaking shapes form and affects phase and frequency. J Comp Physiol 107:13–37Google Scholar
- Franke HD (1980) Zur Determination der zeitlichen Verteilung von Fortpflanzungsprozessen in Laborkulturen des PolychaetenTyposyllis prolifera. Helgoländer Meeresunters 34:61–84Google Scholar
- Franke HD (1985) On a clocklike mechanism timing lunar-rhythmic reproduction inTyposyllis prolifera (Polychaeta). J Comp Physiol A 156:553–561Google Scholar
- Franke HD (1986) Sex ratio and sex change in wild and laboratory populations ofTyposyllis prolifera (Polychaeta). Mar Biol 90:197–208Google Scholar
- Hauenschild C (1955) Photoperiodizität als Ursache des von der Mondphase abhängigen Metamorphose-Rhythmus bei dem PolychaetenPlatynereis dumerilii. Z Naturforsch 10b:658–662Google Scholar
- Hauenschild C (1960) Lunar periodicity. Cold Spring Harbor Symp Quant Biol 25:491–497Google Scholar
- Neumann D (1969) Die Kombination verschiedener endogener Rhythmen bei der zeitlichen Programmierung von Entwicklung und Verhalten. Oecologia 3:166–183Google Scholar
- Neumann D (1981) Tidal and lunar rhythms. In: Aschoff J (ed) Biological rhythms (Handbook of behavioral neurobiology, vol 4). Plenum Press, New York, pp 351–380Google Scholar
- Pittendrigh CS (1981a) Orcadian systems: Entrainment. In: Aschoff J (ed) Biological rhythms (Handbook of behavioral neurobiology, vol 4). Plenum Press, New York, pp 95–124Google Scholar
- Pittendrigh CS (1981b) Circadian organization and the photoperiodic phenomena. In: Follet BK, Follet DE (eds) Biological clocks in seasonal reproductive cycles. Wiley, Bristol, pp 1–35Google Scholar
- Pittendrigh CS, Minis DH (1964) The entrainment of circadian oscillations by light and their role as photoperiodic clocks. Am Nat 98:261–294Google Scholar
- Pittendrigh CS, Bruce VG, Kraus P (1958) On the significance of transients in daily rhythms. Proc Natl Acad Sci USA 44:965–973Google Scholar