Sexual selection in mice. VI. Effects of fostering

Individually, 10 male mice of both the albino (ST/bJ) and black-agouti (CBA/J) strains were taken at birth, fostered to females of the other strain, and reared with their litters. At weaning each male was paired with one of its foster brothers and placed in a separate cage. When the males were 90 days of age, a single albino (ST/bJ) female was placed in each pen. Ten litters were obtained from each competition cage, yielding a total of 100 litters for each type of fostering. In those cases where CBA males had been reared with ST litters, both males were equally successful in reproduction. However, in the reverse situation, where ST males had been reared with CBA litters, the ST males enjoyed a distinct reproductive advantage. These results are compared to those obtained in a previous sexual selection experiment, using the same strains of mice but without fostering. In addition, the results of fighting experiments between males from these strains and the implications of those results for the present study are discussed.