Violent phenotype in SAL mice is inflexible and fixed in adulthood

Violence was shown to be qualitatively different from functional hyper-aggression in mice selected for high aggression namely Short Attack Latency (SAL), Turku Aggressive (TA) and North Carolina (NC900) strains. This study aimed at investigating whether this adulthood violent phenotype as seen previously in the SAL mice is fixed and hence behaviorally inflexible right from day 1 of the experiment or consequential, i.e., subject to gradual change from functional aggression to violence. The functionally hyper-aggressive strains namely TA and NC900 strains served as controls for the study. Methodologically, behavioral (in)flexibility was studied using the overall sequential structure of agonistic behavior. In particular, intra-individual variations in the overall agonistic behavior as well as offensive, pre- and post-offensive behavior transitions, directly related to the resident–intruder interactions were investigated. The SAL mice showed the least intra-individual variation in their overall sequential agonistic structure as well as a fixed offense-oriented agonistic behavior of highest magnitude when compared with the other strains. Additionally, the pre- and post- offensive transitions were most salient in the functionally hyper-aggressive TA and NC900 strains, whereas virtually absent in the SAL mice. Thus, the violent behavior of the adult SAL mice is behaviorally inflexible or fixed, whereas the functionally hyper-aggressive behavior of the adult TA and NC900 mice is behaviorally flexible and constantly adaptive to the opponent behavior, over 3 days of repeated resident–intruder interaction.