The effects of fluoxetine and metformin pollution on phenotypic traits and gene expression in Daphnia magna

Interest in the effects of pharmaceutical pollution on aquatic habitats has expanded with the growing number and increased distribution of drugs worldwide. In this study, we perform an experiment to examine the effects of two drugs, fluoxetine (known commercially as the anti-depressant Prozac™) and metformin (a widely-used diabetes medication), both of which are common freshwater contaminants. We investigated the effects of the two drugs alone and in combination on Daphnia magna in both in crowded and non-crowded conditions in order to understand how pharmaceutical pollution and naturally-occurring environmental cues might interact to shape phenotypic traits and gene expression. We assayed fecundity, respiration, transgenerational effects, and gene expression levels for three genes. Pharmaceuticals affected offspring, respiration, and gene expression, while crowding affected fecundity. Specifically, fluoxetine induced male production and metformin made offspring sickly. Overall, these drugs and their combination had detectable impacts on many traits, and in some cases the effects depended on crowding conditions. Daphnia, a model system in ecology and ecotoxicology, provides myriad insights into the effects of pollutants, both because of its key role in freshwater food webs and its ability to serve as an experimental system to determine sublethal and lethal effects. Our findings contribute to our current understanding of pharmaceutical pollution and suggest that investigating the risks using more real-world scenarios is important for the maintenance of freshwater drinking supplies and freshwater ecosystems.