Studies on Sexual Selection in Mice. II. Reproductive Competition between Black and Brown Males

Abstract

Ten male mice of the black strain, C57BL/6J, were randomly paired with ten males of the brown strain, C57BR/cdJ. Each pair was then placed in a cage with a brown female. Ten litters were obtained from each pen giving a total of 100 litters. All males were proven fertile both at the beginning and at the end of the experiment. It was found that 70 per cent of the litters were sired solely by black males, 16 per cent solely by brown males, while 14 per cent of the litters were the results of double inseminations (mixed litters). Within the mixed litters there were more brown offspring than black. There was no statistical difference in litter size among the three types of litters. Out of a total of 788 mice born in the ten cages, 606 (77 per cent) were fathered by black males while only 182 (23 per cent) were sired by brown males. The results are compared to those obtained in an earlier experiment.