Task complexity as a factor in eliciting heterosis in mice: aversively motivated behaviors.

Three inbred strains of mice (A/J, DBA/2J, and C57BL/6J) and their six reciprocal F1 hybrids were tested in activity levels before and after shock, inhibitory avoidance, one-way avoidance, and shuttle avoidance. In the activity and inhibitory situations the hybrids generally exhibited an intermediate pattern of inheritance. In the one-way avoidance task complete dominance was the rule, whereas in the shuttle task overdominance was apparent in all the hybrid strains. Overdominance was found to be more evident in tasks requiring increased versatility of associative processes. It is suggested that when the task involves relatively simple contingencies or reflexive behaviors, increased versatility is not necessary and consequently the hybrid advantage is not apparent. When the task involves integrative capacities, the hybrid advantage emerges.