Developmental predictors of an impulsive-aggressive phenotype.

In hamsters, individual differences in offensive aggression are associated with impulsive choice, leading to the characterization of a distinct impulsive-aggressive phenotype. This study had two goals: to determine the developmental trajectory of the maturation of this phenotype and to address its parental lineage. Interestingly, individuals most aggressive as adults were less likely to attack in early puberty. However, looking at the transition of agonistic behavior from play fighting to adult aggression, impulsive-aggressive individuals were less likely to engage in play fighting attacks and more likely to engage in more mature agonistic behavior. Additionally, parental lineages were compared for the aggressive responses expressed by their adult offspring. Most impulsive-aggressive individuals were offspring of few select males, which were more likely to produce this phenotype, without an association with females or specific litters. These findings identify an abnormal and accelerated development of agonistic behavior in impulsive-aggressive individuals and a likelihood of heritability.