Determinants of mating success in the golden hamster (Mesocricetus auratus): II. Pregnancy initiation.

Abstract

One purpose of this study was to investigate the initiation of pregnancy in virgin and multiparous female golden hamsters. A second purpose was to investigate the physiological significance of long intromissions (10-30 s of intravaginal thrusting). Virgin females required significantly less copulatory stimulation to induce pregnancy and maximize litter size. Animals receiving only long intromissions showed a 100% pseudopregnancy rate, a result indicating that long intromissions can initiate the neuroendocrine response necessary to maintain pregnancy. When the male delivered only one or a few ejaculations, the inclusion of long intromissions significantly increased the percentage of both virgin and multiparous females that became pregnant. Multiparous females were employed to test the fertilizing capacity of successive ejaculates from rested males. Order of ejaculations did not affect the proportion of females that delivered litters. However, litter size of females receiving the 1st or 5th ejaculation was significantly larger than that of females receiving the 10th or 15th ejaculation. Multiple-male matings did not augment pregnancy rates or litter sizes compared with matings with a single, rested male.Copulation serves multiple functions in addition to the placement of sperm in the appropriate region of the female reproductive tract. In the laboratory rat a single ejaculation is sufficient to initiate pregnancy and delivery of a normal-sized litter; however, this occurs with a high probability only when six or more intromissions accompany the ejaculation (Adler, 1969;Wilson, Adler, & LeBoeuf, 1965). Following ejaculation the male rat shows a refractory period of 5-11 min in which no copulation occurs. If the female receives further copulatory stimulation (intromissions) during the first 4 min of this refractory period, sperm counts in the uterus are significantly decreased as also is the number of implantation sites (Adler & Zoloth, 1970). In a further examination of these phenomena in the rat, Chester and Zucker (1970) showed that while three intromissions were suffi-This work was supported by Grant BNS-8300892 from the National Science Foundation.We thank N. T. Adler and J. P. Toner for their valuable comments on an earlier version of the manuscript.Requests for reprints should be sent to U.

Mating capacity of male deer mice (Peromyscus maniculatus bairdi) copulating with successive females

“…It appears to be adaptive for females to prefer unmated males, as has been shown for several species (e.g., Huck, Lisk, Parente, & Principato, 1986;Nakatsuru & Kramer, 1982). However, for the deer mice in the present study, the difference in ordinal position related to the failure of males to copulate and ejaculate late in episodes, rather than to their failure to inseminate femalesas effectivelyas they did early in episodes.…”

Influence of time of mating and paced copulation on induction of pseudopregnancy in cyclic female rats

“…Under other conditions in which changes in sensitivity to the stimuli necessary for induction of pregnancy/pseudopregnancy have been demonstrated (i.e. age and parity), the rat and hamster appear to be similar; with advancing age and parity, increased amounts of cervical stimulation are required (Davis et ai, 1977;Huck & Lisk, 1985;Huck et ai, 1988). However, the rat and the hamster differ in the types of copulatory stimuli received during mating and differ in the numbers of intromissions or ejaculatory series required for pregnancy initiation (Huck & Lisk, 1985).…”

“…age and parity), the rat and hamster appear to be similar; with advancing age and parity, increased amounts of cervical stimulation are required (Davis et ai, 1977;Huck & Lisk, 1985;Huck et ai, 1988). However, the rat and the hamster differ in the types of copulatory stimuli received during mating and differ in the numbers of intromissions or ejaculatory series required for pregnancy initiation (Huck & Lisk, 1985). For the hamster, it is not known precisely when in the circadian cycle the nocturnal prolactin surge occurs (Greenwald, 1985), and it is possible that in this species the timing of this surge coincides with the period of highest sensitivity to cervical stimulation.…”

Paternity assessment in free-ranging wild boar (Sus scrofa) – Are littermates full-sibs?

“…Otherwise, if females mated in sequence with different boars, stronger evidence of multiple paternity would be found since heterospermic inseminations produce littermates sired by different males (Berger 1995;Stahlberg et al 2000), and multiple paternity occurs when gilts mate in succession with different boars (Martinl and Dzuk 1977). Huck et al (1985) proposed that female precopulatory guarding should evolve if there is first male sperm precedence, and conversely that post-copulatory mate guarding should evolve if there is last male sperm precedence. In S. scrofa as both first and last-copulatory males are able to sire offspring it seems likely that a boar would gain fertility advantage over competitors by expending long time in copulatory mate guarding, either in pre and post-copulatory guarding.…”