Determinants of mating success in the golden hamster (Mesocricetus auratus): I. Male capacity.

Rested adult golden hamsters produced a mean of 13 ejaculations and then showed a modified copulatory pattern consisting of long intromissions (10-30 s of intravaginal thrusting) during which no sperm transfer occurs. When a second (fresh) female was introduced, 58% of the males produced at least one more ejaculation, and 17% of the males produced one further ejaculation when placed with a third female. In similar three-female tests conducted 24 hr later, all males ejaculated (M = 4 ejaculations); this level of ejaculatory output was maintained over a subsequent 10-day period of daily testing. Four ejaculations ensured a nearly 100% pregnancy rate and maximum litter size in the first females. Second and third females, however, received fewer ejaculations and subsequently showed reduced fertility and produced smaller litters. Most males showed high levels of long intromissions on all days and with all females. The physiological significance of these long intromissions may be to trigger the progestational response. Examination of the rate of recovery from sexual exhaustion indicated that 2 or 8 hr of rest resulted in fewer than 50% of the males being capable of one further ejaculation. However, most of these single ejaculations were accompanied by long intromissions and resulted in successful pregnancies. Four to eight days were required for full recovery of ejaculatory capacity. This study showed that the male golden hamster has a higher ejaculatory output and more rapid recovery from sexual exhaustion than other small rodents that have been studied. Thus, the limits of male capacity appear to vary widely among species.