Functional analysis of maternal aggression in the house mouse (mus musculus domesticus).

The presumed function of maternal aggression as a means to protect the young from infanticidal conspecifics was tested. Lactating females attacked male intruders regardless of their potential for infanticide and intrasexual aggression (as previously screened). The level of aggression of the male intruder rather than his infanticidal potential, influenced both the mother's latency to attack and the possibility of successful protection of her young. A lactating female's attack on a male, but not on a female, intruder was reduced by the presence of her mate. Lactating females did not attack male intruders when their mates were not aggressive towards them. Thus, maternal attack appears to be modulated by the aggressive characteristics of both the stud and the intruder male rather than as a response to the potential risk for the litter. This suggests that lactating female attack on males is not only a counter-strategy to infanticide. In an evolutionary perspective, the possibility that this behavior may also involve intersexual selection mechanisms is discussed.