Circannual and circadian rhythms in the snailHelix aspersa M�ller and the photoperiodic control of annual activity and reproduction

Abstract

1. Individual adultHelix aspersa show a circadian rhythm of locomotor activity when kept in constant darkness, temperature, and high humidity. 2. When kept for 14 months at temperatures with little annual variation from a mean of 17.4 °C, but with photoperiod varying in step with the seasons, snails moved and fed least during the short days from October to April. This is the time of hibernation in the field. Mating and egglaying ceased in September. All activities were resumed when days lengthened in January, before hibernation ends in the field. 3. When transferred from the field to a photoperiod regime reversed by six months, snails re-phased their normal annual cycle of locomotor and reproductive activity to become most active in the long days. 4. In an unvarying photoperiod of 12 h, snails exhibited a circannual cycle of movement, feeding, and reproductive activities which was faster than the normal annual cycle.