Testosterone treatment produces sex-dependent effects in social dominance

Dominance hierarchies reduce the costs of competitive aggression in social animals, and testosterone is a proposed mediator of aggressive behaviour and social dominance. While the effects of testosterone on male behaviour are well studied, effects on female aggression and dominance within mixed-sex groups are less clear. We tested how short-term testosterone treatment influences aggressive behaviour and dominance hierarchies in the common waxbill, Estrilda astrild, a bird with mild social hierarchies. In captive mixed-sex groups, we administered intramuscular testosterone to either males or females and, using a test of competition for food, compared aggressive behaviour and social dominance to those of a control treatment (saline) with no testosterone administered. Testosterone treatment to males increased their social dominance, without increasing aggression. We observed a decrease in female aggression towards treated males, suggesting that females were reacting to subtle cues of male dominance (e.g. vocal cues). In contrast, female treatment with testosterone did not increase their dominance, which could either be due to a lack of effect on females, or because males reacted to and opposed cues of female dominance. Together, our results indicate a sex-dependent role of testosterone on social hierarchies. (c) 2021 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.