Phase-shifting and Entrainment of a Circadian Rhythm in Limulus polyphemus by Ocular and Extraocular Photoreceptors

Author： Renninger G Lajoie C Brad Hanna W J Fong D House C Zelin J

ISSN： 0929-1016

Source： Biological Rhythm Research, Vol.28, Iss.1, 1997-11, pp. : 50-68

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Abstract

Illumination of just the telson of the horseshoe crab Limulus polyphemus produced increasing phase-shifts in the circadian rhythm of the ERG amplitudes of the compound lateral eye with increasing length of exposure to light, up to 12h for 10-h exposures, equal to the phase-shifts produced by illumination of the whole animal or of the anterior photoreceptors alone. Periodic illumination of the anterior photoreceptors or of just the telson entrained the lateral eye rhythm, which reliably re-entrained when the phase of the illumination was shifted by ±6h. Illumination for 10h of one compound eye alone or of the median ocelli alone produced small phase-shifts. Periodic illumination of just one compound lateral eye could be arranged to entrain the rhythm of the other compound eye, but the rhythm did not always re-entrain following a ±6h phase-shift in illumination. The apparent redundancy in circadian photoreceptors may be useful to Limulus in dealing with the various photic environments which it inhabits.