Copulatory behaviour and differential reproduction of laboratory rats in a two-male,one-female competitive situation

In order to relate copulatory behaviour to differential reproductiion, 20 Long-Evans and 20 F344 male rats were observed in both one-male and two-male tests with an F344 female. Copulatory behaviour was quite similar in the two conditions, although there were some quantitative differences. Little fighting occurred. Long-Evans males attained 56% of the ejaculations and sired 76% of the offspring. The first male to ejaculate gained no advantage with respect to siring offspring. By contrast, the male ejaculating last or most frequently gained a significant reproductive advantage. Far from being wasted activity, persistent copulation in male rats plays an integral role in differential reproduction.