Abstract
Androgens, namely 11-ketotestosterone (11KT), have a central role in male fish reproductive physiology and are thought to be involved in both aggression and social signalling. Aggressive encounters occur frequently in social species, and fights may cause energy depletion, injury and loss of social status. Signalling for social dominance and fighting ability in an agonistic context can minimize these costs. Here, we test the hypothesis of a ‘chemical diplomacy’ mechanism through urinary signals that avoids aggression and evokes an androgen response in receiver males of Mozambique tilapia (Oreochromis mossambicus). We show a decoupling between aggression and the androgen response; males fighting their mirror image experience an unresolved interaction and a severe drop in urinary 11KT. However, if concurrently exposed to dominant male urine, aggression drops but urinary 11KT levels remain high. Furthermore, 11KT increases in males exposed to dominant male urine in the absence of a visual stimulus. The use of a urinary signal to lower aggression may be an adaptive mechanism to resolve disputes and avoid the costs of fighting. As dominance is linked to nest building and mating with females, the 11KT response of subordinate males suggests chemical eavesdropping, possibly in preparation for parasitic fertilizations.
Highlights
Androgens, synthesized mainly in the gonads and adrenal tissue[1], are essential in vertebrate reproductive physiology and behaviour[2]
The mechanisms underpinning male aggression have been suggested to be associated with androgens[2, 11,12,13,14], which are responsive to social challenges[15, 16]; circulating levels usually rise in winners[17, 18], increasing the probability of winning ensuing fights and the willingness to engage in further disputes[17, 19], and they may fall in losers[20]
Prior to the mirror test, there were no differences in the initial levels of urinary cortisol and 11KT between fish stimulated with dominant male urine (DMU) or control water
Summary
Androgens, synthesized mainly in the gonads and adrenal tissue[1], are essential in vertebrate reproductive physiology and behaviour[2]. The mechanisms underpinning male aggression have been suggested to be associated with androgens[2, 11,12,13,14], which are responsive to social challenges[15, 16]; circulating levels usually rise in winners[17, 18], increasing the probability of winning ensuing fights and the willingness to engage in further disputes[17, 19], and they may fall in losers[20]. In social species where dominance signals are reliable predictors of conflict outcome, both winners and losers benefit from ritualized interactions Both may use signals to convey fighting ability and motivation; the individual signalling higher dominance wins more often, and without recourse to violence[32,33,34,35,36,37]. Other cichlids have been shown to signal dominance chemically through faeces[53] and to mediate aggressive interactions in male-male encounters through the emission of urine pulses[54]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
