The copulatory behavior of both wild and domestic strains of Rattus norvegicus was observed via continuous video monitoring as it spontaneously occurred in the large seminatural environment and under standard laboratory conditions. A factorial design demonstrated that the female Norway rat has the major role determining the amount and timing of copulation once mating begins. Copulation between wild pairs was characterized by fewer ejaculatory series than domestic pairs. The first ejaculatory series of wild pairs contained more intromissions at longer intervals. Domestic pairs had the same total number of intromissions in a copulatory session, but spread over multiple ejaculatory series with few intromissions at short intervals in the first series. The characteristic differences between the copulatory patterns of wild and domestic pairs was determined by the female's strain condition and was either statistically independent or opposite to the male's strain condition. Specifically, the population pattern of a wild female was characterized by fewer ejaculatory series and more intromissions at longer intervals before the first ejaculation than the pattern of a domestic female. These differences between wild and domestic populations were produced by differences in the rate of active solicitations for an intromission by individual females : the solicitation occurred virtually in a one-to-one correspondence with an intromission. There were no gross anatomical differences between the vaginal size and placement of the two strains. The female solicitation is a distinct and quantifiable behavior not found in the standard testing cage: its occurrence depends on a larger and more complex environment. In addition, copulation in the larger seminatural environment is characterized by fewer intromissions in each ejaculatory series of a session at longer copulatory intervals. The role of the female is discussed both in terms of the individual interactions which underlie it and in terms of its physiological functions for successful reproduction in the rat. Copulation with a wild male is characterized by longer intervals between the intromissions of the first ejaculatory series than with a domestic male. The wild condition of both the pair and the female showed the opposite effect. This difference is evaluated in terms of the different mating strategies for the two sexes on a population level and in terms of the individual interactions that allow a compromise for successful reproduction of the pair.

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Recordings of neuronal activity in the pudendal, genitofemoral, and pelvic nerves indicate that the sensory fields of these three nerves are the perineum, the caudal abdomen, and the vagino-cervical area and rectum, respectively. The sensory field of the pudendal nerve was significantly larger in estrogen-treated ovariectomized female rats than in uninjected controls. This effect of estrogen was not mediated by pudendal efferents.

Six experiments were performed to investigate the effects of the rat's copulatory behavior on sperm transport in the female's reproductive tract. Data showed that (a) transcervical sperm transport in rats requires 6-10 min after ejaculation for completion; (b) transcervical transport of large numbers of sperm requires that the vaginal plug remain lodged tightly in the vaginalcervical junction; (c) maintenance of an immobile posture by the male, and possibly by the female, at ejaculation facilitates the deposition of a tightly lodged vaginal plug and the transport of large numbers of sperm through the cervix; (d) a single intromission occurring within 2 min after ejaculation disrupts sperm transport, but more copulatory stimulation is required to disrupt sperm transport when delivered between 4 and 10 min after ejaculation; and (e) the average postejaculatory interval is long enough to prevent a male from disrupting the transport of most of his own sperm from the preceding ejaculation.