Aggression as a component of relative fitness in four inbred strains of mice.

In four separate experiments, male mice from the RF/J, BALB/cJ, DBA/2J, and C57BL/6J strains were grouped in a seminaturalistic environment with ,females from the C57BL/6J strain. Observations were made concerning the aggressive behavior of the different strains, and starch gel electrophoresis of the esterase III and hemoglobin proteins was used to determine paternity of the offspring. Results indicated that the most aggressive strain, RF/J, sired 95.6% of all offspring. Control groups indicated that the reproductive disadvantage of the BALB and C57 males could be explained in terms of differences in general fertilizing ability, the effects of grouping mice together, or pregnancy blockage. These factors alone were not sufficient to explain the disadvantdge of the DBA males. Differences in fighting success may therefore be an important determinant of fitness differences between RF and DBA males.