The impact of nocturnal light pulses on the activity pattern of terrestrial snails (Helix lucorum) entrained to a photoperiod of 12 h light: 12 h dark

Abstract

The effects of nocturnal light pulses, "asymmetrical skeleton photoperiod regimes," on the circadian locomotor activity rhythm in adults of the edible snail Helix lucorum previously entrained to a photoperiod regime of 12 h light : 12 h dark were examined. In all experiments the snails showed a clear bimodal rhythm of behaviour, with peaks at both dusk and dawn. Shifts occurred according to the timing of 2-h light pulses applied in the scotophase and were related to the phase of snails' entrained rhythms. It is suggested that a minimum dark period (up to 10 h) is necessary for H. lucorum to retain its normal daily rhythmicity.