To pee or not to pee: urine signals mediate aggressive interactions in the cooperatively breeding cichlid Neolamprologus pulcher

The communication of aggressive propensity is an important component of agonistic interactions. For this purpose, animals use different sensory modalities involving visual, acoustical and chemical cues. While visual and acoustic communication used in aggressive encounters has been studied extensively in a wide range of taxa, the role of chemical communication received less attention. Here, we studied the role of chemical cues used during agonistic interactions of territory owners in the cooperative cichlid Neolamprologus pulcher. During staged encounters, we allowed either visual and chemical contact between two contestants or visual contact only. As chemical information in this species is most likely transferred via urine, we measured urination patterns using dye injections. Furthermore, we recorded aggressive and submissive behaviours of both contestants in response to the experimental treatment. Fish that had only visual contact with each other significantly increased their urination frequency and showed more aggressive displays compared to fish with both visual and chemical contact. Furthermore, appropriate agonistic responses appear to be dependent on available chemical information. This indicates that N. pulcher actively emits chemical signals to communicate their aggressive propensity via urine. Chemical communication thus plays a crucial role in multimodal communication of aggression in these fish, which highlights the need of studying the role of chemical communication during agonistic encounters in general, even if other signals are more obvious to the human observer. Significance statement The communication of aggressive tendencies can be achieved by transmitting visual, acoustical and chemical information. In this context chemical communication received less attention than other modalities thus far. We studied the importance of chemical information released via urine during agonistic encounters in the cooperatively breeding cichlid N. pulcher. Using dye injections, we measured urination patterns as well as the aggressive and submissive behaviours of two contestants. We show that N. pulcher actively signals aggressive tendencies via altered urination patterns. Furthermore, we show that appropriate agonistic responses appear to be dependent on the availability of such chemical information. Thus, our results suggest that chemical communication plays a crucial role in multimodal communication of aggression in these fish. These findings highlight the importance of chemical communication during agonistic encounters in general, even if other signals are more obvious to the human observer.