Exposure to an anti-androgenic herbicide negatively impacts reproductive physiology and fertility in Xenopus tropicalis

Amphibians are threatened on a global scale and pollutants may be contributing to population declines, but how chemicals impact on their reproduction is poorly understood. We conducted a life cycle analysis to investigate the impacts of early life exposure to two anti-androgens (exposure until completion of metamorphosis;stage 66): futamide, (50µg/L)/linuron (9 and 45µg/L)) on sexual development and breeding competence in Xenopus tropicalis. Our analyses included: mRNA levels of dmrt1, cyp17, amh, cyp19, foxl2 and ar (tadpoles/metamorphs), gonadal histomorphology (metamorphs/adults), mRNA
levels of ar/gr (adult male brain/gonad/forelimb), testosterone/corticosterone levels (adult males), secondary sexual characteristics (forelimb width/nuptial pad: adult males) and breeding competence (amplexus/fertility: adult males). Compared to controls, feminised sex ratios and increased number of
spermatogonia (adults) were observed after exposure to futamide and the lower linuron concentration. Exposure to the lower linuron concentration also resulted in demasculinisation of secondary sexual characteristics and reduced male fertility. Flutamide exposure resulted in masculinisation of the nuptial
pad and elevated mRNA levels of dmrt1, cyp17, amh and foxl2 in brains (metamorphs). Testosterone levels were higher in all treatment groups, however, overall few efects were observed in response to the higher linuron concentration. Our fndings advance understanding of reproductive biology of X. tropicalis and illustrate negative efects of linuron on reproductive processes at a concentration
measured in freshwater environments.