Behavioural interseasonal adaptations in Daphnia pulicaria (Crustacea: Cladocera) as induced by predation infochemicals

A wide range of chemical signals have been demonstrated to affect the swimming behaviour of Daphnia, including molecules associated with predation threat. In this contribution, we investigate how the concomitant presence of kairomones from the predaceous fish Lepomis macrochirus and alarm pheromones from crushed conspecifics affect the small-scale swimming behaviour of Daphnia pulicaria. In particular, we studied both the light/dark and summer/winter variations in the swimming motion of the cladoceran in the presence and absence of these infochemicals, and related them to the limnology of the environment. At summertime temperature, in the presence of light and infochemicals D. pulicaria confined its motion to the first few centimetres of the observation vessel, expressing positive phototaxis. In all other conditions, instead, no significant difference in the time spent in the upper and lower parts of the chamber was recorded. The upward displacement of D. pulicaria recorded in our experiments deviates from the most traditionally accepted downward migration used to move into darker layers to avoid visual predation. Our results highlight additional behavioural mechanisms that might be efficiently exploited by D. pulicaria to contrast predation by L. macrochirus.