Mate calling behavior of male South African clawed frogs (Xenopus laevis) is suppressed by the antiandrogenic endocrine disrupting compound flutamide

Abstract

Several environmental pollutants have been identified as antiandrogenic endocrine disrupting chemicals (EDC), with flutamide (FLU) being a model compound for this type of action. Despite impacts of EDC interfering with sexual differentiation and reproduction in amphibians, established information about suggested effects on sexual behavior is still lacking. In this study adult male Xenopus laevis were injected with human chorionic gonadotropin (hCG) to initiate mate calling behavior. After one day hCG-stimulated frogs were treated via aqueous exposure over three days without and with FLU at concentrations of 10(-8) and 10(-6) M in comparison to untreated frogs. Androgen controlled mate calling behavior was recorded during the 12h dark period. At the end of exposure circulating levels of testosterone (T) and 17beta-estradiol (E2) were determined and furthermore gene expression was measured concerning reproductive biomarkers such as hypophysial luteinizing hormone (LH), follicle-stimulating hormone (FSH), testicular aromatase (ARO), 5alpha reductase type 1 (SRD5alpha1) and 5alpha reductase type 2 (SRD5alpha2). Both concentrations of FLU caused a significant decrease in calling activity starting at the second day of exposure. HCG injected positive controls had elevated levels of T compared to negative control frogs while in parallel treatment with FLU did not affect significantly the hCG elevated sex steroid levels. Furthermore, hCG treatment led to significantly decreased levels of gene expression for ARO and SRD5alpha2 but no impacts were detected on LH, FSH or SRD5alpha1 mRNA levels compared to negative controls. In summary, the behavioral parameter mate calling is the most sensitive biomarker detecting antiandrogenic modes of action in this challenge-experiment indicating that this non-invasive method could markedly contribute for sensitive assessment of antiandrogenic EDC.