SELECTIVE BREEDING FOR ISOLATION-INDUCED INTERMALE AGGRESSION IN MICE- ASSOCIATED RESPONSES AND ENVIRONMENTAL-INFLUENCES

Aggressive (TA) and nonaggressive (TNA) lines of mice were established by selective breeding for isolation-induced intermale aggression. Thi s paper summarizes and updates studies performed on the TA and TNA lin es. The genetic analysis revealed that in these lines the genes for ag gression are located on the autosomes and demonstrate a Mendelian segr egation The genes are expressed only in the presence of androgens whic h are normally present only in males. Behavioral and biological respon ses associated with high and low levels of aggression in TA and TNA mi ce are reviewed. Line differences have been found in olfactory communi cation and marking behavior, in maternal and predatory aggression in f emales, in locomotor activity, and in learning abilities. Also, correl ated neurochemical and endocrinological responses to the selection hav e been detected. Maternal factors during the preweaning period do not significantly affect the development of aggression in TA and TNA males , while early postweaning exposure to aggression or sex enhanced later aggressive and sexual activity. Early experience and genetic disposit ion for aggression are correlated, with TA males showing the greatest increase in the behaviors studied.