The influence of reproductive state on infanticide by wild female house mice (Mus musculus).

The majority of female mice (Mus musculus) from laboratory stocks are spontaneously parental. In contrast, the majority of adult wild female house mice exhibit infanticide (the killing of preweanling young), but the frequency with which infanticide is observed varies as a function of age and reproductive state. Prepubertal females were less likely to exhibit infanticide (39%) than were adult virgin females (61%). The frequency of infanticide increased during pregnancy, with over 90% of females exhibiting infanticide just before parturition. But, after parturition, previously infanticidal females cared for their own litters. When lactating female mice were tested after two days of separation from their own nursing young for their behavior toward a novel newborn pup on either the tenth or twenty-fifth day after parturition, the proportion of the females that exhibited infanticide was not significantly different from that of adult virgin females (about 60%). After only two hours of separation from their own nursing young on the tenth day after parturition, however, all females continued to exhibit parental behavior toward a novel pup.