Endogenous circadian changes in orientational behaviour ofTalitrus saltator

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Abstract
Orientated navigational behaviour inTalitrus saltator(Montagu) was studied throughout the diel cycle. Amphipods released at the centre of a circular arena without an artificial horizon on the periphery showed random escape directions at all times of day. In the presence of an artificial light/dark boundary the escape direction was random at night but was towards the boundary by day. The onset of significantly orientated navigation occurred just before the time of dawn and persisted in a typically circadian manner for 7 days in amphipods kept in continuous darkness.The phase of the circadian rhythm could be reset in altered light/dark cycles. Phase changes were directly proportional to imposed L:D phases over the range —4 to + 12 h, except that shifts from —2 to +2 h induced no phase change in the orientation rhythm. The endogenous pattern of change of orientated navigation is discussed in relation to the nocturnal endogenous locomotor activity rhythm ofTalitrusand its diel pattern of foraging and burrowing behaviour on sandy beaches.