Building upon previous work studying legacy contaminants in the Duwamish River urban watershed in Seattle, WA, we investigated impacts of pyrethroids on aquatic invertebrates at the foundation of the food web. Pyrethroids are the active compounds found in common pesticides, which previous studies have shown interfere with the closure of sodium channel gates in invertebrates. To examine pyrethroid impacts, we integrated toxicology and behavioral ecology into experiments on isopods (Gnorimosphaeroma oregonesis), one of the most abundant invertebrates in the contaminated river. We hypothesized that the presence of pyrethroids would interfere with isopod's ability to sense and react to danger cues, due to disruption of sodium channel gate function. To identify sublethal behavioral responses, we tested two types of pyrethroids, Bifenthrin (I) and Cyhalothrin (II), at three concentrations: 1.5 ng/mL (LD50), 0.25ng/mL (ED50), and 0.05 ng/mL. Our experimental setup tested isopod phototaxis across six treatments: control, pyrethroid, hemolymph, predator, hemolymph + pyrethroid and predator + pyrethroid. To quantify differences in behavior, we observed isopod abundance in dark versus light areas of the experimental chambers.
Results/Conclusions
Isopods exhibited no preference for light or dark areas in the control and pyrethroid treatments. When exposed to danger cues (hemolymph or predator), isopods were significantly more abundant in dark areas of the experimental chambers, as expected. However, when exposure to hemolymph and predator cues was combined with pyrethroids, isopods again showed no preference. These results were consistent across both types and all concentrations of pyrethroids. Overall, our experiments indicate that pyrethroids diminish isopod's negatively phototactic response to danger cues, which could increase their vulnerability even at low concentrations, with potential ramifications for the food web.