Intraspecific maternal aggression in the house mouse (Mus domesticus): a counterstrategy to infanticide by male?

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Abstract
A series of experiments was carried out to assess whether the «defensive» pattern of female parental attack towards sexually naive male conspecific intruders, in which there is no inhibition against biting vulnerable areas of the intruder's body, could function as a deterrent to infanticide. Primiparous lactating mice (Mus domesticus) which had not previously displayed parental attack showed clearly differentiated patterns of biting attack when confronting sexually naive male and female conspecific intruders, respectively. Males intruders were more prone to kill pups than were female counterparts, and this behaviour was facilitated in the absence of the mother. Remarkably, lactating females simultaneously confronting a virgin female and a sexually naive male intruder attacked only the latter animal. These data suggest that lactating female aggression serves as a counterstrategy to male infanticide. Nevertheless the mother's aggressive behaviour delayed but rarely thwarted the killing of pups by males that had dominated the female and that were characterized by high levels of social aggression in previous intermale aggression tests. Maternal attack was successful in defending the litter from those males that were incapable of defeating the lactating female and that were characterized by low levels of intermale aggression. Consequently, maternal aggression might also function, as a by-product, to prevent reproduction by males of poor fighting ability. The hypothesis that in this context female aggressive behaviour towards the interloper male could also be involved in intersexual selection is discussed.