Endocrine Disrupting Compounds Alter Risk‐Taking Behavior in Guppies ( P oecilia reticulata )

Endocrine disrupting compounds ( EDC s) enter aquatic habitats from a variety of anthropogenic sources and can mimic, block, or modulate the synthesis of natural hormones. EDC s affect both reproductive and non‐reproductive behaviors because hormones mediate responses associated with aggression and fear. We examined the effects of two EDC s on risk‐taking behaviors in guppies ( Poecilia reticulata ). We quantified risk‐taking in terms of propensity to forage in a risky location and tendency to join groups in the presence of a predator. We found that male and female guppies responded oppositely to environmentally relevant concentrations of an estrogenic EDC , 17α‐ethinylestradiol ( EE 2), or an androgenic EDC , 17β‐trenbolone ( TB ). Males decreased risk‐taking with increasing EE 2 concentration (as predicted), but females increased risk‐taking (contrary to prediction). In contrast, females increased risk‐taking with increasing TB concentrations (as predicted), but males decreased risk‐taking (contrary to prediction). These results did not match our expectation that EE 2 would reduce risk‐taking and TB would increase risk‐taking in both sexes. We suspect EE 2 and TB produced these counterintuitive effects by downregulating their corresponding hormone receptors and thus reducing levels of circulating endogenous hormones in females and males, respectively. These results show that EDC s can alter fish behavior and potentially reduce fitness in unexpected ways.