Chemical cues released from both plants and animals are thought to impact the behavior of Daphnia. Daphnia dentifera, native to Sites Lake, OH (40^oN, 82^oW) is thought to alter its behavior when exposed to kairomones from planktivorous fish or similar signals from aquatic plants. The small size of these organisms (<1.2mm) impedes the ability to effectively monitor their behavior in experimental tanks. To enhance their visibility, a method was developed in which Daphnia were fed transgenic Escherichia coli labeled with the Green Fluorescent Protein (GFP). GFP-labeled E. coli fluoresce when exposed to UV light. They can be seen microscopically, using a fluorescent microscope, or macroscopically, using a black light.

Results/Conclusions

Initial studies revealed that D. dentifera do consume the GFP-labeled E. coli, but that gut fullness varies up to a maximum of 94%. Timed incubation studies showed that gut fullness of Daphnia increased linearly (y=0.0116x-0.0989; R²=0.87). We extrapolated from these data to estimate that a 95–minute incubation will be necessary to achieve maximum gut fullness.  We are conducting further experiments to establish conditions that optimize animal visibility in aquaria using this approach. This method may prove to be an essential tool for future studies analyzing the behavior demonstrated by Daphnia dentifera and other small species.