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L. C. Drickamer

Summary. Females housed at a density of 8 mice/cage had to be grouped for a minimum of about 10 days before their urine was capable of producing delays for first vaginal oestrus in test females comparable to the delays occasioned by treatment with urine from females grouped for 30 days or longer. Young test females had to receive a minimum daily exposure of 1–2 h to the chemosignal to produce the complete delay of puberty.

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L. C. Drickamer

Summary.

The relationships between the size and sex composition of the litter and puberty in female mice were investigated. Both factors significantly affected the age of first vaginal oestrus; litter size accounted for 22% of the total variation in age at puberty, and litter sex composition for 8 %. When no males or only one male was present in litters of 10 young the females matured significantly earlier than when two or more males were present.

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L. C. Drickamer

Summary. Mice were maintained in rooms with constant ambient conditions and a 12 h light: 12 h dark daily light regimen with the lights on starting at 06:00 h. In Exp. I, detection of puberty, as measured by first vaginal oestrus, was recorded at significantly earlier ages when vaginal smears were taken at 04:00 or 08:00 h than at other times of the day. In Exp. II, adult females were detected as being in oestrus more frequently when vaginal smears were taken within 6 h before or after the onset of the light part of the cycle each day than at other times.

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L. C. Drickamer

Summary. Three separate experiments tested whether the seasonal variation in the effectiveness for accelerating or delaying puberty in female conspecifics of male urine, urine from pregnant or lactating females, and urine from females housed in groups is attributable to seasonal changes in the quality of the chemosignals released by the donor mice or to seasonal shifts in the sensitivity to the chemosignals for recipient females or to some interaction between these two factors. Six-by-six cross-classified designs were used with urine collection taking place in alternate months for 1 year and urine treatments with samples from all 6 collection months applied in the same alternate months in the subsequent year. For all three urinary chemosignals the seasonal variations in chemosignal effectiveness were determined to be a function of changes in recipient sensitivity and not of any seasonal shifts in the chemosignals released by donor mice. Seasonal variations in body weight at weaning were also a contributory factor in determining the age of first vaginal oestrus. Covariance analyses revealed that, even after adjustment of the treatment means for the seasonal differences in body weight, there were significant effects on the age of puberty due to seasonal shifts in recipient sensitivity, but not with respect to the month in which the urine was collected.

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L. C. Drickamer

Summary. Four types of chemosignal donors were used: adult intact males, grouped adult intact females, pregnant females and lactating females. A daily dose of 0·001 ml urine was sufficient to produce the same degree of acceleration or delay known to occur with whole urine from each donor type. With 0·00001 ml the age of puberty did not differ from that of water-treated controls for any of the treatments. With the intermediate, 0·0001 ml/day dose, the results were variable, depending upon the donor type. The results indicate that for young mice daily exposure to extremely small quantities of urine can influence the physiological events accelerating or delaying puberty.

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L. C. Drickamer

Summary. Female mice previously selected for early and late sexual maturation were tested to determine whether they retained flexibility in age of puberty in response to pheromonal and social cues. First vaginal oestrous in fast-maturing females could be delayed but not accelerated by social cues. Conversely, puberty in slow-maturing females could be accelerated in their sexual development, but not delayed. Two additional experiments demonstrated that mice from the fast- and slow-maturing lines retained the capacity to accelerate and delay puberty via pheromonal and social cues.

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L. C. DRICKAMER

Summary.

The present experiment utilized a cross-classified design to test the interactions and relative importance of male presence or absence, female density and three different photoperiods as factors affecting puberty in female house mice. First vaginal oestrus was used as the criterion for sexual maturity. All three factors significantly affected the timing of first oestrus; male presence or absence accounted for 31% of the total variation in age at maturity, 9% of the variance was attributable to the female density factor and 6% to differences in daylength treatments. There were no significant interactions among the treatment variables. These results conform with a general model relating the processes of sexual and morphological development.

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L. C. Drickamer

Summary. The effects of donor age on the effectiveness of puberty-influencing urinary chemosignals in wild house mice was tested in a series of 3 experiments. The chemosignal from male mice that accelerates puberty was present in the urine from about the time of puberty and throughout the normal lifespan, but declined about 1 year of age. Oestrous females released a substance in their urine that accelerates puberty in young females. This substance remained effective from first oestrus until over 1 year of age, although older females were in oestrus less frequently than younger mice. Females that are pregnant or lactating released a puberty-accelerating substance in their urine regardless of age. Production and release of the puberty-delaying chemosignal by grouped females was initiated before puberty and continued throughout the lifespan of the mouse.

Keywords: mouse; chemosignals; puberty; first oestrus; age; pregnancy; lactation

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L. C. Drickamer

Summary. A series of 9 experiments was conducted to examine various characteristics of the urinary chemosignal found in the urine of oestrous female mice that accelerates the sexual development of conspecific females. This urinary chemosignal was effective in doses as small as 0·001 ml/day, was present in excreted and bladder urine, required 3 days of treatment starting before Day 29 of age to effect an acceleration of puberty, required a minimum daily exposure of 2 h, and was relatively nonvolatile. In addition the chemosignal from oestrous females was effective in summer but not in winter months, was significantly more effective when collected at the middle or end of the dark portion of the daily cycle than at the beginning of the dark phase or middle of the light phase, and was not affected by food deprivation or shortened photoperiod. Simultaneous treatment of test subjects with urine from oestrous females and grouped females resulted in delays in puberty and simultaneous treatment with urine from oestrous females and urine from males or pregnant or lactating females did not result in any enhanced acceleration of puberty.

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L. C. Drickamer

Seven experiments were performed to investigate pregnancy termination, urinary chemosignals, and litter sex ratio variation in female house mice. Experiments tested the effects of urine from adult and prepubertal females, housed individually or in groups, on successful insemination and litter production by females treated at different times and for different periods during the 3 weeks before mating and during gestation. Treatment of females with urine from adult females housed eight per cage or with urine pooled from eight adult females housed individually for 2 or 3 weeks before mating resulted in fewer successful pregnancies and significantly more female-biased litters. Treatment with urine from adult or prepubertal females housed eight per cage or with urine pooled from eight mice housed individually for the first 6 days of gestation or throughout pregnancy resulted in a significant increase in the rate of pregnancy termination. These treatments resulted in lower body weights at birth and slower growth rates in all males and in some females. Puberty was delayed in female progeny from urine-treated dams in five of seven experiments, and these young females attained first oestrus at greater mean body weights than mice in other treatments. These findings indicate that, in mice, at high population density, communication via a urinary chemosignal can alter reproduction in recipient females. Availability of, and competition for, resources such as food would be greater at higher densities, possibly lowering the probability of reproductive success. Pregnancy termination and delays in reproduction and attainment of sexual maturity might lead to greater successful reproduction at a later time.