Infanticide by virgin CF-1 and wild male house mice (Mus musculus): effects of age, prolonged isolation, and testing procedure.

The frequency of infanticide by juvenile, young-adult, and adult male house mice (Mus musculus) was compared in CF-1 albino mice and the F1-F4 male offspring of wild mice trapped in Missouri. When tested in their home cages for their behavior toward a single 2-day-old pup after being individually housed for 5 days, juvenile CF-1 and wild males were equally likely to exhibit infanticide (about 35%). But, adult wild males were significantly more likely to exhibit infanticide (about 90%) than were adult CF-1 males (about 45%). We propose that differences in exposure to testosterone during fetal life may contribute to the difference in the incidence of infanticide between CF-1 and wild males. Prolonged isolation (45 days) significantly reduced the proportion of wild male mice that exhibited infanticide when the males were tested in their home cages, but not when the males were tested by being placed into the cage of lactating females and their 2-day-old young. Virtually all adult wild males exhibited infanticide when they were tested in their home cages (with either a 2-day-old or 7-day-old pup) or when they were placed into the cages of lactating wild female mice and their 2-day-old young. But, when adult wild males were placed with lactating wild females on Day 7 postpartum, the females attacked the males and most males were prevented from exhibiting infanticide.