Factors affecting incidence of infanticide and discrimination of related and unrelated neonates in male Mus musculus.

Infanticide by males was examined in two strains (C57B1 and DBA) of the house mouse (Mus musculus). Males that had contact with a female within the previous 2-3 weeks rarely committed infanticide when introduced to the home cage of a female and her 1-day-old neonates, even when the female and neonates were of a different strain and from a different colony. In contrast, 90% of C57B1 males that had no contact with a female for more than 7 weeks killed pups when placed in the female's home cage, and 60% killed when a 1-day-old pup was introduced to the male's home cage. No difference in levels of infanticide occurred when grouped males were compared to isolated males. These results indicate that infanticide is not dependent upon recognition of the pups or the female, but depends on the male's previous exposure to females. Infanticidal behavior is not directly determined by genetic relationship, but the factors that inhibit this behavior reduce the probability that a male will kill his own offspring.