The bachelorette: Female Siamese fighting fish avoid males exposed to an estrogen mimic

Abstract

Due to improper disposal and a lack of removal during the wastewater treatment process, endocrine disrupting chemicals enter aquatic ecosystems where they exert detrimental effects on fish behavior and physiology. Perhaps the most well-studied and prevalent EDC is 17α-ethinylestradiol (EE2), an active ingredient in oral contraceptives, which is known to cause dramatic reductions in male-typical behaviors. While it is likely that alterations in male courtship behavior decrease reproductive fitness, this is rarely explicitly examined. To this end, whether EE2 exposure reduces male attractiveness to female Siamese fighting fish, Betta splendens, was investigated by showing females video images of exposed and unexposed males. Females were randomly assigned to one of two exposure conditions (exposed to EE2, control) and each subject then viewed four different video combinations of male conspecifics (courting exposed+exposed; courting unexposed+unexposed; courting unexposed+exposed; swimming unexposed+exposed). Females, regardless of whether or not they were exposed to EE2, directed markedly less behavior towards exposed males, especially when they viewed an exposed male and an unexposed male simultaneously. These findings demonstrate that EE2 can have significant individual- and population-level consequences on fitness by disrupting sexual selection and, ultimately, the success of exposed males.