Sexual aggression in mice: effects of male strain and of female estrous state.

We have observed that 50% of FVB/NtacfBR ("FVB") males were aggressive toward females in tests of mating behavior. We decided to gather basic evidence for an effect of genotype on this behavior by testing for strain differences between FVB and C57BL/6J ("B6") male mice. Also, hypotheses developed from theoretical work on sexually coercive behavior suggest there should be a cycling effect on sexually aggressive behavior (Smuts and Smuts, 1993). We tested for an estrous cycling effect by using stimulus females in a state of either estrus or diestrus. Both strains modulated mating behavior to female cycling state. Cycling state did not modulate B6 aggression. FVB males were more aggressive than B6 males, and cycling state modulated their behavior. We conclude that sexually aggressive male mice modulate aggressive behavior to female social signals and indicate how this data can be used to study the genetics of sexual aggression.