Opposite strain‐dependent differences for intermale aggressive behavior elicited by individual housing and housing with a female in the mouse

Male mice of the C57BL/6 strain show a significant increase in aggression toward a nonaggressive male conspecific following 72 hr of individual housing. However, this increase was no longer evident following 2 weeks of individual housing. When housed with a female, C57BL/6 mice show significantly more aggression than singly housed mice of the same strain after 72 hr as well as 2, 4, 8 weeks of differential housing. Male C57BL/6 mice housed with a female also show significantly higher levels of aggression than DBA/2 mice living in the same housing condition after 4 or 8 weeks of differential housing. Finally, male DBA/2 mice individually housed for 8 weeks are significantly more aggressive than mice of the same strain housed with a female for the same time. These results indicate that the increase in aggressive behavior observed following isolation and cohabitation with a female in the mouse is not the same phenomenon. © 1994 Wiley‐Liss, Inc.