Direct genetic and maternal influences on behavior and growth in two inbred mouse strains

Newborn male DBA/2 and C57BL/6 mice were either crossfostered, fostered within strains, or, after handling, left with their own dams and compared for nine behavioral compenents observed in single animals at an adult age and for body weight measured at 4 weeks and 3 months. Many strain differences between the unfostered control groups emerged and these remained largely unchanged in comparisons between the infostered and between the outfostered groups. In neither infostered group were significant influences of fostering per se found. Some variation due to foster strain was detected mainly in the DBA outfostered group, namely, for 4-week body weight, rearing frequency, and locomotor activity, but no resemblance to the alien strain was brought about by this. Effects of litter occurred rarely. Unlike the C57BL strain, the DBAs showed a clear pattern of interdependence among exploratory acts. In spite of problems that may be attached to the crossfostering method, it was concluded that postnatal genotype-dependent maternal influences were rather unimportant as a source of variation in behavior and growth as measured between these two strains, relative to direct genetic effects and, possibly, prenatal factors.