Agonistic behavior among animals is a tool to establishing social and regular hierarchy. Reproductive success is closely related to the level of aggressive behavior exhibited during the reproductive activity. Aggressiveness may be manifested in a context of competition by means of fight or conflict in the dispute over access to food, shelter or sexual partners. These disputes include offensive fights with assessment, direct agressions, body injuries and defenses. The present study aims to investigate the effect of reproductive state and sex on the agonistic behavior of the Amazonian cichlid Mesonauta insignis. Initially we describe the patterns of agonistic behavior exhibited by adult fish of the species and evaluate the dynamics of their agonistic interactions (Chapter 1). We also aim to compare the aggressive displays of Mesonauta insignis adults in reproductive and non-reproductive state. In addition, we compare the aggressive interaction of females and males and analyzed the effect of the opponent's gender on the tactics of fights used in aggressive intrasexual and intersexual encounters of Mesonauta insignis adults (Chapter 2). An etogram was prepared, composed of eight agonistic behavioral units that were separated into three classes: assessment, aggression and defense and classified according to their intensity: low, medium or high intensity. The dynamics of the agonistic interaction indicated a scaling of the behavioral units towards the end of the conflict, suggesting the corroboration of the sequential evaluation model. The adults of the species showed a higher level of aggressiveness when they are in the reproductive state. Males showed longer latency times to engaje the conflict than females. Intersex encounters were more often won by males. This study suggests that this cichlid species compete more aggressively in the reproductive season, increasing the probability to defend important reproductive resources, and that females and males show distinct aggressive tactics, probably boosted by selective pressures acting differently in each sex.
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