Habituation, sensitization, and redirection of aggression and feeding behavior in the three-spined stickleback (Gasterosteus aculeatus L.).

Three-spined stickleback males maintained in individual aquaria built nests and defended the entire aquarium as a territory. Adjacent compartments containing another male stickleback, a gravid female, or a nongravid female provided a social context within which to study the habituation and sensitization of aggression elicited by a conspecific male intruded into the subject's territory. Typical sensitization-habituation curves were found for all fish regardless of the kind of neighbor. However, behavior redirected as a result of the stimulation of the intruded male differed between conditions. The group with a male neighbor showed increased aggression toward the neighbor, the group with a gravid female neighbor showed courtship, and the group with nongravid female showed neither. A third behavior, nest building, showed no difference between conditions, a result providing little evidence for a simple explanation in terms of general arousal. A second experiment elicited the same motor response to the intruded stimulus, but the motivational category was changed by eliciting the behavior by presenting live brine shrimp. In this experiment, aggression did not change during habituation, but the waning predation was redirected to another food-securing behavior, picking at the substrate. The results provide evidence for the important role that social context plays in understanding the redirection of behaviors, a phenomenon predicted from an extension of the dual-process theory of habituation.