Methyl-Testosterone Induces Male-Typical Ventilatory Behavior in Response to Putative Steroidal Pheromones in Female Round Gobies ( Neogobius melanostomus ) Cheryl A. Murphy 1 and Norm E. Stacey Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada T6G 2E9 Received December 1, 2000; revised July 7, 2001; accepted February 6, 2002 Male round gobies ( Neogobius melanostomus) tran- siently increase their rate of ventilation when exposed to nanomolar concentrations of three putative steroidal pheromones (etiocholanolone, ETIO; estrone, E1; estra- diol-glucuronide, E2-3g), whereas females exhibit this response only to ETIO. In this study we implanted females with Silastic capsules that were empty (Blank) or filled with methyl-testosterone (MT) to determine whether androgen induces a male-typical pattern of ven- tilatory response. As with untreated females in our pre- vious studies, Blank females increased ventilation only in response to ETIO. In contrast, MT females tested 2–3 weeks postimplant responded not only to ETIO, but also to E1 and E2-3g. These results provide the first demon- stration of an androgen inducing a male-typical behav- ioral response to a steroidal pheromone in adult female fish. Together with our previous findings of sexually iso- morphic sensory responses to steroid odorants, the present results also suggest that a central action of androgen is responsible for sexually dimorphic behav- ioral responses to putative pheromonal steroids in Neogobius. © 2002 Elsevier Science (USA) Key Words: round goby; Neogobius melanostomus; sex pheromones; steroid; behavior; ventilation; sexual di- morphism; masculinization; methyl-testosterone; androgen. Behavioral, endocrine, and electro-olfactogram (EOG) studies indicate that many fish have evolved to use released hormones (steroids, prostaglandins, and their metabolites) as potent pheromones that induce repro- ductive, physiological, and behavioral responses in conspecifics (Sorensen and Stacey, 1999; Sorensen, Christensen and Stacey, 1998; Stacey and Cardwell, 1995, 1997). The majority of fish hormonal pheromone studies have dealt with sex-typical responses in the orders Cypriniformes (e.g., goldfish, Carassius auratus; Sorensen, 1992; Stacey and Cardwell, 1997), Siluri- formes (African catfish, Clarias gariepinus; Van Den Hurk and Resink, 1992), and Salmoniformes (e.g., At- lantic salmon, Salmo salar; Waring, Moore, and Scott, 1996). There also have been reports of hormonal pher- omone use in the large and economically important order Perciformes (e.g., black goby, Gobius niger (= G. jozo); Colombo, Belvedere, Marconato and Bentivegna, 1982, and an African cichlid, Haplochromis burtoni; Ro- bison, Fernald and Stacey, 1998). In this study, we report that exogenous androgen induces male-typical behavioral responses to putative steroidal phero- mones in females of a perciform fish, the round goby, Neogobius melanostomus. Exogenous androgen induces male-typical endocrine response to the steroid phero- mone 17,20-dihydroxy-4-pregnen-3-one (17,20-P) in goldfish (Kobayashi, Furukawa, Kim, and Aida, 1997). However, the results of the present study pro- vide the first demonstration that androgens can in- duce male-typical behavioral responses to a hormonal pheromone in adult female fish. Sexual plasticity of the brain has been documented in many species of teleost fish (Kobayashi, Stacey, Aida, and Watabe, 2000; Godwin, Sawby, Warner, Crews and Grober, 2000; Foran and Bass, 1999; Grober and Sunobe, 1996). Indeed, the widespread occurrence of sequential (protogynous and protandrous) her- 1 To whom correspondence and reprint requests should be ad- dressed at current address: Department of Oceanography and Coastal Sciences, Coastal Fisheries Institute, Wetlands Resources Building, Louisiana State University, Baton Rouge, LA 70803. Fax: (225) 578-6513. E-mail: cmurph4@lsu.edu. Hormones and Behavior 42, 109–115 (2002) doi:10.1006/hbeh.2002.1810 0018-506X/02 $35.00 © 2002 Elsevier Science (USA) All rights reserved. 109