Studies on Wild House Mice. VII. Prenatal Maternal Environment and Aggression

The effect of the maternal environment on intermale aggression was studied by means of embryo transfer of genetically selected aggressive (SAL) and nonaggressive wild house mice (LAL), and their reciprocal F1's, to standard (NMRI) females. No effect was found on the attack latency scores (ALS), i.e., aggression: all genotypes born and raised under natural conditions showed an ALS similar that of genotypes born and raised by NMRI females. Since previous studies on wild house mice failed to demonstrate postnatal effects on aggression, and the present results indicate the absence of prenatal maternal environmental effects on aggression, the primacy of genetic over maternal variance in the development of adult intermale aggression in wild house mice is indicated

Individual Differences in Disease Susceptibility as a Possible Factor in the Population Dynamics of Rats and Mice

Factors affecting health and disease are somewhat neglected in the study of the dynamics of mammalian populations. The present paper summarizes a number of studies on social stress in rats and mice. Social situations induce classical stress responses in terms of corticosterone and catecholamines. More important is the fact that there is a considerable individual differentiation in the magnitude of the responses in relation to the behavioural stategy in a social situation. These physiological differences render individuals differentially susceptible for stress pathologies such as cardiovascular diseases and immune deficiencies. Moreover, the behavioural strategy largely determines the position of an animal in the social structure and hence the frequency of behavioural and physiological activation. The data suggest that the individual behavioural and physiological reactivity determine in interaction with the social environtment the susceptibility for diseases. The relevance of these observations for the dynamics of a population is discussed.