Nuances in fish combat: Exploring male and female differences in the agonistic behavior of an Amazonian cichlid

Agonistic interactions are present in the competition for limited resources in virtually all groups of social animals. However, little is known about the ways males and females dispute resources or defend or care for offspring. Here, we investigated how the contests between adults of the Amazonian flag cichlid (Mesonauta insignis (Heckel, 1840)) take place in intra- and intersex encounters in a neutral environment, and whether males and females are able to fight equally for the same resources. We captured individuals in the wild and staged size-matched encounters under controlled conditions. Our analysis revealed distinct contest phases, with statistical differences in aggressive unit frequency and time spent specifically between phase 1 and phase 2, corroborating an escalation dynamic. Half of those contests showed distinct phases, and a clear escalation in aggression and in injury risk. Although both sexes expressed the same levels of aggression and the same cost of contest in their engagements, other sexual differences in their aggressive interaction strategy were detected. Males proved to be more cautious when engaged in same-sex contests. Contest costs increased with body size of females in same-sex and in intersex encounters. We discuss the implications of our results in supporting the idea that both sexes of Amazonian flag cichlids engage in agonistic encounters to achieve similar goals, but they show sex-specific aspects when doing so. This study provides valuable insights into the ecological and behavioral drivers, such as distinct escalation dynamics and sex-specific competitive strategies, in cichlids.