In the intertidal homing gastropod onchidium verruculatum (Cuv.) the outward and homeward trails have a different information content

Abstract

At low tide Onchidium verruculatum (Cuv.) emerge from holes or crevices in rocks to graze. They can find home again by retracing a trail laid down during the outward journey. When animals going to or from home are placed at 90° to the outward trail they usually turn and follow it towards the origin (i.e. towards home). Homeward-bound animals are more responsive to the trail than are outward-bound animals. Trails contain directional information because tested animals still turn mostly towards the origin of trails rotated 180° (i.e. they turn away from home). Animals heading home show few positive responses to their inward path, whether or not this is rotated. Similarly, when they are shifted to sand, animals that were outward-bound when moved show more positive responses to their trails than animals that were inward-bound. Directional information may be strongly present only in the outward trail: on the return path the polarized trail is either switched off or its information content is reduced. Trails are individual-specific. Faeces are produced throughout the feeding excursion but they are probably not the source of trail information.