Phototactic behaviour and neurotransmitter profiles in two Daphnia magna clones: Vertical and horizontal responses to fish kairomones and psychotropic drugs

Animal behavioural responses are increasingly being used in environmental risk assessment. Nevertheless, behavioural responses are still hampered by a lack of standardisation. Phototactic behaviour in zooplankton and in particular in Daphnia has often been associated to vertical migration but there is also 'shore-avoidance' horizontal behaviour. Daphnia uses shades along the shore to swim either to or away from the shore and predators. Previously, we develop a vertical oriented behavioural hardware able to reproduce phototactic fish induced depth selection in Daphnia magna, its modulation by fish kairomones and psychotropic drugs and the neurotransmitter profiles associated to those responses. This study aims to test if it is possible to use an horizontal 24 multi-well plate maze set up to assess phototactic fish induced responses in D. magna. The study was conducted using two clones with opposed phototaxis upon exposure to fish kairomones and using psychotropic drugs known to modulate phototaxis. Acrylic strips opaque to visible light but not to the infrared one were used to cover half of the arena of each of the wells of the multi-well plate. Clone P(1)32,85 showed positive phototaxis in either the vertical and horizontal set up and negative phototaxis when exposed to fish kairomones or to the muscarinic acetylcholine receptor antagonists scopolamine and atropine. The opposite behaviour was observed for clone F. Diazepam and pilocarpine ameliorate fish kairomone induced negative phototaxis and picmtoxin increased it only in clone P(1)32,85 in the vertical set up. The determination of ncumtransmitters showed much greater concentrations of dopamine and of glycine in clone F, which may be relate to its negative phototaxis and its observed lower responsiveness to fish kairomoncs. The results from this study suggest a simple, fast, and high throughput phototactic behaviour assay for D. magna that can be easily adapted to other species.

Automated summary

Animal behavioural responses are increasingly used in environmental risk assessment, but the lack of standardization remains a challenge. This study aimed to test the use of a horizontal multi-well plate maze set up to assess phototactic fish induced responses in D. magna. The results suggest that this method could provide a simple and efficient way to evaluate phototactic behavior in D. magna and potentially other species.