Effects of early life exposure to methylmercury on predator response in daphnia pulex

Knowledge of the health effects of toxic chemicals is largely based on single chemical models rather than a multi-factor model, which more accurately captures realworld exposures. This study investigated how methylmercury affects Daphnia pulex in the presence of predatory stress chemical. A kairomone is an infochemical released by an animal that can be detected by another animal. Daphnia pulex detects kairomone released by Danio rerio resulting in the induction of morphological and life history changes. Danio rerio were kept in COMBO media for 24 hours at a density of 2 fish per liter. Daphnids were then housed in kairomone-containing COMBO for their full life cycle. Following this kairomone exposure, adult females were additionally exposed to 1600 ng/L of methylmercury for 24 hours in the absence of food. Female offspring were collected every 48 hours and measurements were taken of tail-spine and body length (central body including head) as well as soma width to determine the impact of the combined exposure on these morphological end-points. Life history traits observed included life span and brood size. Our data shows that maternal exposure to methylmercury had a significant negative impact on the predatory responses including tail spine and body size (length and width) in offspring two days old or less. Brood size was not significantly impacted in this system; however, life span was significantly lessened. These data demonstrate the necessity of using multi-factor models in testing the toxicity of environmental exposures in bio-sentinels.