The effects of 17α-ethinyloestradiol on boldness and its relationship to decision making in male Siamese fighting fish

Behavioural syndromes have received much attention by behavioural ecologists in recent years. While the relationship between boldness across contexts and between boldness and aggression are frequently investigated, little is known about how these relationships might change because of environmental disturbances such as exposure to endocrine disrupters. 17α-ethinyloestradiol (EE2) is an oestrogen mimic that is prevalent in aquatic ecosystems worldwide and has severe, negative impacts on the behaviour and physiology of exposed organisms. To assess how EE2 affects boldness and decision making, male Siamese fighting fish, Betta splendens, received repeated trials of three boldness assays (novel environment, empty tank and novel object) and one decision-making assay (a dummy male and female presented simultaneously) before and after exposure to acute, nominal doses of EE2. A control group of males received the same number of trials but was not exposed to EE2. When subjects were unexposed, a behavioural syndrome was found for boldness across contexts. In addition, boldness was positively correlated with aggression in the decision-making context. EE2 exposure disrupted this behavioural syndrome. In summary, EE2 exposure reduced overall behavioural response in all contexts, disrupted the behavioural syndrome and reduced behavioural consistency. Thus, even nominal, short-term exposure to EE2 can have dramatic effects on multiple levels of behaviour and potentially generate severe fitness consequences on exposed aquatic species. This study provides the first evidence of a boldness–aggression syndrome in this species and demonstrates that pollution may negatively influence consistent individual differences in behaviour.