Behavior of Biomphalaria glabrata (Gastropoda: Pulmonata) under different lighting conditions

Abstract

The preferred position, the surface contact area of the head–foot, and the locomotor activity of Biomphalaria glabrata were studied in a laboratory aquarium throughout the year. The snails were more frequently found on the walls and on the bottom than on the surface. Under two regimes of illumination their frequency of occurrences were different. The extent of the head–foot outside the shell increased from spring or summer to winter, and was significantly correlated negatively with temperature rather than illumination. Movement increased from summer to winter. Under artificial vertical lighting in the natural day cycle in group conditions two daily peaks become evident, at dusk and sunrise. Abrupt changes of illumination, especially during dusk, were discriminative cues for exogenous control of locomotion. Under constant darkness and in constant light, the level of locomotion was significantly lower than that under a natural day cycle of illumination, but in both regimes, locomotion was not significantly different; therefore, absolute illumination did not change the level of locomotion. In both regimes, snails were no longer synchronized to the solar rhythm. The threshold for natural light perception was around 20 lx, when photokinesis appeared during the winter. Photokinesis increased with locomotion and both activities varied inversely with temperature.