Overview and Meaning
Agonistic interactions allow one animal to gain control of actual or future resources or otherwise increase its reproductive success at the expense of a second animal in a social interaction.
Agonistic Interactions are a top-level classification, reflecting a Behavior chain of individual goal-directed behaviors, which behavior typically follows a two-to-four-stage sequence:
Agonistic interactions can occur in the context of territorial behavior, and/or dominance behavior. Territorial behavior and dominance behavior differ in both the context that they occur, the resources under competition, and the threat behavior that initiates the interaction.
Unlike exploration the chain typically proceeds in a fixed sequence. Both Aggressive behaviors and Defensive behaviors may be omitted. These differences have very distinct meanings, and are of critical importance to the interpretation of agonistic interactions.
- The inclusion of Aggressive behaviors (stage 2) is the key distinction between Escalated aggression from Mediated aggression, where Aggressive behaviors are seen in Escalated aggression but not Mediated aggression. In observing home-cage behavior, this is by far the most important distinction to make. Mediated aggression normally represents the vast majority of mouse agonistic interactions, and is widely misinterpreted in the literature. In contrast, Escalated aggression occurs when a subordinate responds to a threat behavior with an aggressive behavior, most typically an aggressive bite. Escalated aggression, as the name implies, escalates until one animal shows flight and submissive behavior, or, in a worst-case scenario, is killed or castrated. (Male mice attempt to castrate each other when they fight, and consequently withdraw their testicles into the body cavity during aggression). In terms of both assessing welfare, and assessing social competence (as might be desirable in an assay for social deficits relevant to Autism), distinguishing these classes of agonistic interaction is particularly useful.
- The inclusion of Defensive behaviors are seen if Flight and Submissive behavior fails to end the agonistic interaction. This potentially indicates a lack of social competence on the part of the aggressor, and also a lack of space or structural complexity in the cage which would enable Flight behavior.