Meeting Abstract

P2.6  Thursday, Jan. 5  Blocking Gonadal Steroid Receptors Affects Sexually Dimorphic Communication Signals in a Weakly Electric Fish FERNANDEZ, D.; SMITH, G.T.*; Georgia State University; Indiana University

Brown ghost knifefish (Apteronotus leptorhynchus) continuously produce weak electric organ discharges (EODs) for electrolocation and communication. During courtship and aggression, these fish transiently modulate EOD frequency (EODf) and EOD amplitude to produce signals known as chirps. EODf and chirping are sexually dimorphic and steroid-sensitive. Males have higher EODf and chirp more often than females. Androgen treatment masculinizes EODf and chirping in females, and estrogen treatment feminizes EODf in males (Schaefer and Zakon 1996; Dunlap et al. 1999). We examined the effects of blocking androgen and estrogen receptors to further test the hypothesis that sex differences in EODf and chirping are regulated by these hormones. Adult males and females in reproductive condition were housed in water that contained the androgen receptor blocker flutamide (0.5 mg/L), the estrogen receptor blocker tamoxifen (0.1 mg/L), or vehicle (ethanol, 0.0025%) for three weeks. Before and after treatment, EODs and chirps were recorded by using playbacks of simulated conspecific EODs. Flutamide lowered (feminized) EODf in males, but not in females. Tamoxifen increased (masculinized) EODf in both sexes. Neither flutamide nor tamoxifen significantly affected chirp rate. Our results suggest that activational effects of androgens and estrogens contribute to sex differences in EODf, but that sex differences in chirping might be regulated by other mechanisms (e.g., organizational effects of hormones or non-steroidal mechanisms). Supported by NSF IOS 0950721.