Mating under the influence: male Siamese fighting fish prefer EE2-exposed females

Countless pharmaceuticals and endocrine disrupting chemicals (EDCs) exist on the market with more added each day. Many of these compounds are not removed during the wastewater treatment process and enter bodies of water in their active form. EDCs are known to have physiological and behavioral effects in exposed organisms. Exposure to the synthetic estrogen 17α-ethinylestradiol (EE2), a common EDC found in birth control pills, has been found to lead to population collapse after only a few generations in some fish species. Mechanisms identified as potential driving forces for collapse include feminization of males and altered fecundity in both sexes. However, an additional way in which EE2 could lead to population collapse is by altering courtship behavior, which could then change mating preferences and decrease mating opportunities. The current study had the following objectives: determine if exposing female Siamese fighting fish, Betta splendens, to EE2 changes mate choice in males; assess if the dose and duration of female exposure matters; and examine if exposing males to EE2 influences their mating preferences. Both unexposed and exposed males were presented with pairs of females that differed in EE2 dose and exposure duration. The results indicate that males were more responsive to EE2-exposed females than unexposed females, with males being most responsive to females exposed to the low versus high dose. Furthermore, exposed males responded less overall than unexposed males. If EE2 concentration increases in the environment, the likelihood of successful mating could decrease and, therefore, potentially lead to adverse population impacts.