RESUMEN
Breeding clouded leopards (Neofelis nebulosa) ex situ has been a challenge, primarily due to extreme and often fatal male aggression toward females. This study's aim was to determine the degree to which two possible mechanisms-serotonergic pathways and circulating testosterone levels-affect aggressive behavior. Male clouded leopard behavioral and hormonal data were collected during a series of behavior tests administered before and after treatment with either an anxiety-reducing tricyclic antidepressant (clomipramine) or a GnRH agonist (deslorelin). Results showed that clomipramine treatment decreased "overall activity" (P = 0.054) and increased "lying down" (P = 0.0043) and hiding in a "nest box" (P = 0.0023). Clomipramine treatment also decreased the incidence of "growling" during a mirror image stimulation test, relative to non-test periods (P < 0.0001 pre-drug treatment; P = 0.242 peri-drug treatment), indicating reduced aggression. Suppression of the reproductive axis via deslorelin treatment resulted in significant decreases in circulating androgen (P < 0.0001) and glucocorticoid (P < 0.0001), accompanied by decreased aggressive behaviors, including "swatting" (P = 0.0476), "tail flicking" (P = 0.0409), and "growling" during the behavior reaction tests: mirror image stimulation (P < 0.0001 pre-drug treatment: P = 0.7098 peri-drug treatment) and unfamiliar people test (P < 0.0001 pre-drug treatment: P = 0.2666 peri-drug treatment) relative to non-test periods. Both drug treatments provide evidence that multiple mechanisms modulate aggressive behavior in the male clouded leopard, suggesting that serotonergic modulation coupled with circulating androgens may aid in the formation of successful breeding pairs. Zoo Biol. 35:474-486, 2016. © 2016 Wiley Periodicals, Inc.