Experimental Analysis of Sexual Behavior of the Deermouse Peromyscus Maniculatus Gambeli

Abstract

AbstractEjaculation in the deermouse Peromyscus maniculatus gambeli was preceded by a sequence of brief penile penetrations (intromissions). In the sexually rested male the number of intromissions preceding the first ejaculation averaged 7 to 8. Each intromission was preceded by a short "bout" of running in which the male pursued the female. Following ejaculation the male failed to mount or investigate the female for the next 6 or 7 minutes. This "refractory period" was terminated when the male achieved another sequence of intromissions and ejaculated again. Males were considered sexually satiated after 30 minutes elapsed without any more ejaculations. Using this criterion it was found that from 3 to 6 ejaculations precede sexual satiation. The refractory periods became progressively longer following each successive ejaculation. If, following satiation, the female was removed and a different female was placed in the test area, all the males achieved additional intromissions and 8 out of 10 ejaculated. When the original mating partner was removed and then returned none of the males achieved ejaculation. This failure to achieve ejaculation with the original female was not due to changes in the condition of the female as a result of copulatory stimulation. Satiated males achieved additional ejaculations with females that had copulated with a different male just prior to the test just as frequently as they did with fresh females that had not copulated for 14 days. The condition of the female as affected by copulatory stimulation did influence other measures of the male's mating performance. These effects were seen most clearly in sexually rested males. The number of intromissions achieved prior to the first and the second ejaculation was greater with females that had received copulatory stimulation just prior to the test than it was with fresh females that had not copulated for 14 days. The time delay between intromissions was longer with fresh females. When males were allowed to achieve their first ejaculation with a fresh female and their second with the same female, there was no change in the number of intromissions from the first to the second ejaculation. This is in contrast to findings with the rat and hamster, in which species a decrease in intromission frequency occurs after the first ejaculation. The current study of the deermouse indicated that if the condition of the female was held constant by testing a male with a fresh female for the first ejaculation and another fresh female for the second ejaculation, a decrease in intromission frequency occurred. On the basis of these results it was concluded that: (i) sexual satiation in the male deermouse is, in part at least, specific to the particular female mating partner, and (2) changes in the condition of the female as a result of copulatory stimulation can have major effects on the "measure of male sexual performance".