Endogenous rhythms of locomotor activity in the high-shore limpet, Helcionpectunculus (Patellogastropoda)

Helcion pectunculus, a high-shore, crevice-dwelling limpet, is active durin g nocturnal low tides and during daytime low tides whilst in the shade. We examined whether this activity is controlled by an internal clock or purely by exogenous stimuli, such as light levels and tidal phase. Maximum entrop y spectral analysis (MESA) revealed that the limpets possess a free-running endogenous rhythm of locomotor activity with both circadian (period 28.1 h ) and circatidal (period 13.8 h) components. We suggest that this rhythm pl ays a role in allowing individuals to avoid unfavourable environmental cond itions. The exogenous entrainment factor of the endogenous circatidal rhyth m in H.pectunculus is the time of exposure to air, whilst the zeitgeber for the circadian component is not yet known. (C) 1999 The Association for the Study of Animal Behaviour.