Long-term effects of accelerated or delayed sexual maturation on reproductive output in wild female house mice (Mus musculus)

The effects of acceleration and delay of puberty in female house mice on survival and reproduction were tested using 6 experimental groups: (1) control females mated at the time of first oestrus, (2) females mated at weaning, (3) females treated with male urine starting at weaning and mated at first oestrus, (4) females housed in groups and mated at first oestrus, (5) females housed alone, treated with urine from grouped females and mated at first oestrus, and (6) females housed alone and mated at 68 days of age. Females caged with males at weaning or treated with male urine and mated at puberty had lower rates of survival to 180 days of age, but did not differ in rates of fertility from mice in the other four treatments. Those females that were housed with males from weaning or treated with male urine also had smaller total numbers of litters, fewer total young, and smaller average litter sizes than did females for which the age of mating was delayed, by grouping or treatment with urine from grouped females, or by being held until age 68 days before mating. Control females mated at first oestrus generally were intermediate or did not differ from the male treatments on these dependent variables. There were no differences in the average number of female young/litter across the 6 treatments. However, females that were delayed in age of first mating had significantly more male young/litter than did females that were accelerated in their sexual development or control females.(ABSTRACT TRUNCATED AT 250 WORDS)     

Acceleration and delay of first vaginal oestrus in female mice by urinary chemosignals: Dose levels and mixing urine treatment sources

The effects of varying dose levels and mixing of urine from various types of donor mice on the age of sexual maturation in female mice were tested. Over the range from 0.001 ml/day to 0.01 ml/day, there was no difference in the effectiveness of male urine in producing acceleration of puberty, nor was there any difference over the same dose range for urine from grouped females bringing about a delay of puberty. Urine from pregnant and lactating females brought about earlier puberty when applied in the higher dose amounts but was not effective in altering the age of first oestrus relative to untreated controls at lower doses. These findings concerning dose levels are important for a full understanding of the behavioural consequences of urinary chemosignals. When urine from different sources was mixed, all treatments which involved urine from grouped females produced delays in first oestrus. The second finding has important consequences for a feedback model for population regulation in house mice involving urinary chemosignals that accelerate or delay sexual maturation and thus shorten or lengthen generation time by affecting reproductive behaviour.     

Effect of density, duration of grouping and age of urine stimulus on the puberty delay pheromone in female mice

The ability of urine from female mice to delay puberty in test females was directly related to the density and duration of grouping of females. When females were removed from group housing their urine lost its ability to delay puberty within 10 days. No interactive effects were observed between duration and density of grouping on the onset of pheromone release after grouping or on the persistence of pheromone release after re-isolation. Urine from grouped females lost its ability to delay puberty in test females after 7 days of exposure to air.     

幼小鼠对种内几种化学信息的识别和反应

50年代以来,国际上相继开展了一些关于化学信息在小家鼠繁殖中作用的研究,并在实验室中揭示了一些反应:如集群雌鼠气味使雌鼠性周期延长的Lee-Boot效应,雌鼠气味能解除集群雌鼠对性周期的抑制、并促使它们同期发情的Whitten效应,以及陌生雄鼠气味中断妊娠的Bruce效应等等。但是,在成鼠间起作用的几种化学信息,是否能被幼鼠感受,对幼鼠的发育和性成熟是否产生影响,还是一个未知的问题。 影响小鼠发育的因素很多,除环境因子外,近来还出现了有关社群因素中外激素对小鼠性成熟影响的报道,发现雄鼠或给予雄激素的雌鼠有促进幼雌鼠性成熟的作用,范志勤发现父本气味和陌生雄鼠气味对幼雌鼠性成熟均有促进作用。但是,目前关于种内雌鼠气味、集群雌鼠气味、幼鼠气味影响性成熟的研究尚不多见。有关各种气味对性成熟效应的比较的报道亦少。本文的目的在于通过实验方法,阐明种内的几种化学信息,诸如父本、陌生雄性、雌性、集群雌性、幼雌等几种气味,对幼雌小鼠性成熟的影响,并据此了解幼鼠识别这几种信息的能力。     

Male-induced puberty acceleration in young female wild mice: hormonal regulation and source of pheromonal cue

Experiments were designed to examine the influence of adult males on the rate of sexual maturation in young female wild mice. In one experiment, young females were raised in presence of adult males, adult females and in absence of any individual, while in another, they were exposed to urines of: (1) castrated males, (2) spayed females, (3) castrated and TP-treated males, (4) castrated and placebo-injected males. Female maturation as measured by age at vaginal opening and first vaginal oestrus was accelerated by presence of adult males, whereas presence of adult females considerably delayed the vaginal opening and the appearance of first oestrus in young females. In the other set of the experiments, urine from castrated or castrated and placebo-injected males was ineffective in inducing early puberty while urine from spayed females highly delayed the sexual maturation. By contrast, urine from castrated and TP-treated males accelerated the puberty more or less like normal males. The results indicate that male's chemosignal accelerating puberty in young females is present in urine and its production is under the control of androgens. However, the female-originating urinary pheromone which delays the puberty in young females is not regulated by ovarian hormones.     

Effects of urine from pregnant and lactating female house mice on oestrous cycles of adult females.

It was demonstrated that mice treated with urine from pregnant or lactating females experienced longer periods of oestrus than did mice treated with water or urine from singly caged females. Application of urine by means of perforated capsules placed in the cage of the test mouse showed that the factor(s) responsible for the longer periods of oestrus was an airborne pheromone. The females experiencing longer oestrous periods ovulated (ova in oviducts), became pregnant and gave birth.     

Urogastrone-epidermal growth factor and aspects of sexual maturation in female rats as a function of age at treatment.

The effect of epidermal growth factor (EGF) on sexual maturation of female rats was studied. A within-litter experimental design was employed, so that in each litter each female received four daily injections of EGF (E, 500 ng/g body weight s.c.) or vehicle (V), at one of three ages: days 0-3 (E1, V1), days 8-11 (E2, V2), days 16-19 (E3, V3). Body weight, pinna detachment, incisor eruption, eye opening, auditory startle, visual placing, vaginal opening and first cytological oestrus were assessed. Neonatal treatment with EGF (E1) delayed pinna detachment and the appearance of the auditory startle, but accelerated eye opening. Also, E1, but not E2 and E3, resulted in lower body weight at weaning. Treatment E3 advanced sexual maturation, as indicated by vaginal opening and first cytological oestrus, by 5-6 days. E1 and E2 had no such effect. Hence the sensitive period for the effect of EGF on female rat sexual maturation is later than that for effects on other developmental characteristics and body weight. In a second experiment, ovary and uterus weights were found not to differ between E3 and V3 females killed on the day of vaginal opening of the E3 rats, suggesting that the effect of EGF may be specifically on the perineal epithelium and not on sexual maturation generally.     

Pregnancy in female house mice exposed to urinary chemosignals from other females.

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.     

Intermittent stimulation and delay of puberty by urinary chemosignals and social contact in wild stock female house mice (Mus Domesticus)

A sequence of six experiments using wild stock house mouse (Mus domesticus) tested the effects of intermittent stimulation with either the urinary chemosignal released by grouped female mice or social contact from grouped females on the age of first vaginal oestrus in young females. Weanling female mice were exposed to bedding soiled by grouped females or cages containing grouped females for 15 min periods, then removed for a prescribed period, and placed again in a cage with soiled bedding or grouped females. The nature of the exposure to the puberty delaying effect, the number of total exposures each day, the total length of exposure to the stimulus, and the total time period over which the exposures occurred were varied. None of the treatment regimes employed here with soiled bedding from grouped females resulted in delays in the onset of first oestrus in test females. Young females exposed to grouped females for 6 or 8 exposures in a 4 h period, 6 or 8 exposures in an 8 h period, or 8 exposures in a 12 h period were significantly delayed in attaining puberty relative to control females that were exposed to cages containing clean bedding. These results are in contrast to earlier findings involving chemosignals that accelerate first oestrus wherein young females exhibited the capacity to accumulate the exposures to the urinary chemosignals from males, females in oestrus and pregnant or lactating females. Direct exposure to the grouped females on an intermittent basis can provide stimulation that is cummulative and results in delays in the onset of first oestrus.     

Investigations on the Olfactory Discrimination Exhibited by the Females in the Male-induced Implantation Failure (the Bruce Effect) in Laboratory Mice

Direct contact with the alien male pheromone for 7 days before mating significantly decreased the rate of male-induced implantation failure (the Bruce effect) in newly inseminated female mice. By contrast, females housed with alien males for 7 days before mating so that physical contact with the latter was prevented exhibited a high rate of implantation failure following exposure to alien males after mating. Exposure to an air-borne pheromone produced by alien males induced oestrus (the Whitten effect) in a significant number of grouped females. The results do not support the suggestion that the inability of the stud male to block implantation is due to his original induction of oestrus. The results also do not support the view that the key factor in the induction of the Bruce effect is the ability of the female to identify the stud as an individual which prevents her from responding to him but allows her to react to a new male with hormonal changes leading to implantation failure and return to oestrus. It is suggested that the olfactory discrimination exhibited by the female in the Bruce effect is influenced by her overall olfactory experience before and after mating. The results are consistent with the view that the male-originating pheromone involved in the Bruce effect is distinct from the one involved in the Whitten effect.     

Social environment and reproduction in female pouched mice, Saccostomus campestris

Pouched mice were kept under controlled conditions of illumination (10D:14L) and temperature (22 +/- 2 degrees C). Age at vaginal opening, first oestrus and first conception did not differ significantly between juvenile females raised singly, in single-sex groups of 5, or with an adult male. After the introduction of a male, sterile cycles and/or matings before first conception were experienced by all females whether they were raised singly or in single-sex groups. Of 10 females raised with a male, 4 conceived at their first mating. Onset of puberty in juvenile females raised with an adult female was delayed, while in juvenile females raised with their families (mother, father and litter mates) only vaginal opening was delayed. However, when raised in family groups without the father, vaginal opening as well as first oestrus were delayed. Grouping of females after weaning, with or without a male, did not change the oestrous cycle pattern. Females in these groups cycled independently of each other and the females grouped with a male also mated and conceived independently of each other. Pregnancy was blocked in 7 of 8 females when the stud male was removed and a strange male was introduced. In females exposed to a succession of males, pregnancy was blocked up to 4 times.     

Excreted urine,bladder urine,and the delay of sexual maturation in female house mice

A series of experiments tested effects of excreted and bladder urine of group- and singly-caged female house mice (Mus musculus) on sexual maturation of young female mice caged alone or in groups of eight. Puberty was determined by vaginal smears. A maturation-delaying pherompne was present in bladder urine of all female mice and excreted urine of group-caged females, but not in excreted urine from singly-caged females. Test mice treated with bladder urine homogenized with urethras from singly-caged females matured at the same age as controls. Apparently the urethras or associated glands of singly-caged females produce a substance which deactivates the maturation-delaying pheromone contained in bladder urine.     

Age at maturity in cavies and guinea-pigs (Cavia aperea and Cavia aperea f. porcellus): influence of social factors

Age at maturity, a particularly important parameter in the life history of small mammals, contributes greatly to fitness. Social influences on age at maturity have been demonstrated for altricial rodents, in particular, mice. Nothing is known about such effects in precocial small mammals. Wild cavies Cavia aperea are born in a highly precocial state and mature early in life, briefly after weaning. We investigated whether the wild cavy C. aperea and the domestic guinea-pig Cavia aperea f. porcellus reach maturity earlier in the presence of adults of the opposite sex. Juvenile females kept in pairs without males showed first vaginal opening (=oestrus) when 59 days old in cavies and at about 40 days in the guinea-pig. However, in the company of adult males, cavy females kept in pairs reached maturity when about 30 days old, and guinea-pig females when 26 days old. Most cavy females experienced successful pregnancy following first vaginal opening. In cavies, female mass at birth and at first oestrus was not correlated with age at first oestrus. In guinea-pigs, birth mass predicted age at maturity only when a male was present. The growth rate from birth to first oestrus related to age at first oestrus. In the wild cavy, the presence of a male appeared to influence maturation more between days 25 and 30 than earlier in life. Male C. aperea matured and had fully descended testes when about 65–70 days old. All male cavies produced abundant motile sperm from day 75. First successful copulations occurred at about the same age. Surprisingly, the priming effect of the presence of an adult male on female maturation proved stronger in these highly precocial caviomorphs than in altricial rodents investigated so far.     

Effects of donor age on urinary chemosignals that influence the timing of first oestrus in young female house mice, Mus domesticus

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.     

Social influences on reproductive development and fertility in female Djungarian hamsters (Phodopus campbelli).

Social influences on the sexual maturation of female Djungarian hamsters were investigated in two experiments. In the first experiment females were housed from weaning with an adult male, by themselves, or with a weanling sister. Maturation was accelerated in females housed with males as indicated by younger age at first ovulation, increased rates of ovarian and uterine growth, and lower LH levels at some ages. Maturation was delayed in females housed with sisters compared to those housed alone as measured by time of first ovulation and by lower estradiol levels at some ages. The most marked differences between groups occurred 8 to 12 days after weaning, suggesting that events during this period are particularly important in the social mediation of sexual maturation. In the second experiment the effects of reproductive suppression (caused by living with a sister) on the subsequent fertility of females housed with males were examined. If male-female pairs were housed in clean cages, no effects were observed; however, pairs housed in cages previously soiled by the female and her sister had fewer young surviving until 1 week of age despite no differences in the age of pregnancy onset or in the initial litter size. Thus, even cues present in unrenewed soiled bedding may have subtle but long lasting effects on reproductive function.     

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

The present experiment was designed to examine whether changes occur during the course of behavioural oestrus in the sensitivity of the female to copulatory stimulation and in patterns of sexual behaviour which might influence the likelihood of luteal maintenance. Cyclic female rats were mated on the evening of pro-oestrus (21:00 h) or early on the morning of oestrus (05:00 h) and received either 5 or 10 intromissions from males under conditions which allowed or did not allow pacing of contacts with males to occur. During mating, the levels of sexual receptivity, the timing of sexual mounts from males, and pacing behaviours were measured. The occurrence of pseudopregnancy or pregnancy in each animal was determined by examining vaginal smears for 14 days after mating and by examining the uterus for the presence of fetuses at the end of the experiment. At both mating times, pacing of copulation with males increased the likelihood of prolonged luteal activity. However, females were more likely to become pseudopregnant following non-paced mating at 05:00 h than at 21:00 h the previous evening. Of those females receiving an ejaculation during mating, no difference were seen between groups in the incidence of pregnancy. This change in sensitivity to cervical-vaginal stimulation during oestrus was not associated with changes in sexual receptivity or pacing behaviour. The ability of cervical-vaginal stimulation to induce pseudopregnancy therefore increases toward the end of the period of oestrus, but the behavioural mechanisms which regulate receipt of such stimulation remain constant during that time.     

Relationship of vaginal impedance with speed of return to oestrus after weaning, oestrous behaviour, parity and lactation length in cyclic sows

The effect of weaning to oestrus interval, oestrus duration, parity, lactation length, breed and their interactions on changes of vaginal impedance in sows after weaning and during oestrus was examined. The impedance measurements were carried out by a four-electrode method. The interval from weaning to oestrus was significantly longer in sows with the length of lactation 21-25 days than 26-30 days and 31-36 days and in primiparous than multiparous sows. The interval from weaning to oestrus was negatively correlated with the length of lactation (r=-0.21; P<0.05), parity (r=-0.36; P<0.01) and oestrus duration (r=-0.26; P<0.01). The weaning to oestrus interval, oestrus duration, parity and lactation length had a significant effect and the breed of sows had no influence on the vaginal impedance in peri-oestrus. The decrease of vaginal impedance after weaning was delayed in sows with a longer weaning to oestrus interval and in primiparous than multiparous sows. The decline of vaginal impedance during peri-oestrus was more gradual in sows with a longer interval from weaning to oestrus, shorter lactation, primiparous sows and sows with the length of oestrus 36 h and 72 h and more. The nadir of vaginal impedance occurred earlier before oestrus in sows with a shorter oestrus. The interaction of weaning to oestrus interval with parity and oestrus duration and the interaction of oestrus duration with parity significantly affected the vaginal impedance in weaned sows. In conclusion, the weaning to oestrus interval, oestrus duration, parity and lactation length considerably influence the vaginal impedance in sows during peri-oestrus. The findings indicate that the impedance technique may be a useful method for a study of factors and processes that accelerate or slow down the return to oestrus after weaning and affect oestrus duration in sows.     

Oestrus suppression in wild mice: source of pheromonal cue

Regularly cycling female mice attained anoestrus when they were exposed to voided urine or to urine directly collected from the bladder of intact females. In contrast, the urine of spayed females or the clitoral gland homogenate from intact females was found ineffective in suppressing oestrus. The findings thus clearly elucidate the presence of an oestrous-suppressing pheromone in the urine of intact females whether voided or collected directly from the bladder and confirm the oestrogen dependence of the pheromone. Clitoral glands do not seem to have a role in production of this pheromone.     

Sexual motivation in relation to social rank in pair-housed sows

The influence of social subordination on sexual motivation during oestrus was studied using 36 sows of which 24 treatment sows were housed in pairs and 12 control sows were housed individually in 12 and 6 m(2) pens, respectively. Video recordings were made from 07:00 h to 19:00 h during the first 2 days after grouping, which took place 3 days after weaning of the piglets. Based on the aggressive interactions between the pair-housed sows, their rank was determined. From day 4 after weaning, a test for sexual proceptive behaviour was carried out twice daily and back-pressure test was carried out four times daily in order to detect standing oestrus. When standing oestrus had occurred, transrectal ultrasonographical scans were also carried out in order to determine if ovulation took place. The proceptivity test took place in a T-maze with a 2 m x 10 m runway ending in two 1.5 m x 1.5 m goal boxes each adjacent to a stimulus compartment. One compartment contained an adult sexually experienced boar and the other was empty. Latency to and duration of time spent close to the boar and time spent presenting were recorded during the 10-min test period. On the first day that standing oestrus had been detected, a test for sexual receptivity was also carried out by introducing the sow to a mature boar in his home pen (9 m(2)). Sexual- and fear-related behaviour of sow and boar were recorded until mating was terminated or the sow had spent 5 min in the pen without mating being initiated. During oestrus the proceptivity test showed a significant increase (P < 0.05) in the time spent standing close to the boar and in presenting for single-housed sows and for pair-housed dominant sows, but not for subordinate sows. During oestrus subordinate sows spent significantly less time standing close to the boar than the dominant sows (P = 0.01) and the same tended to be the case for presenting (P = 0.07). In the receptivity test more subordinate sows than dominant sows fled (40% versus 0%, P = 0.001) and more subordinate sows than dominant sows squealed (58% versus 15%, P = 0.02) as a response to boar stimulation. In both tests, the single-housed sows differed neither from the dominant nor the subordinate sows. There was however no difference between the groups in the weaning to oestrous interval, duration of oestrus and number of piglet born. In addition, all the sows ovulated. The results indicate that social subordination can have significant consequences for sexual motivation in sows. Subordinate sows showed fear-related behaviour in response to boar stimulation even when they were in standing oestrus. Thus, both heat detection and mating may be impaired in subordinate sows. The results emphasise the importance to alleviate the social stress experienced by subordinates as well as the need for stock people to pay special attention to these animals when they are to be mated or inseminated.     

Role of photoperiod and temperature in production of the oestrus-inducing pheromone in male wild mice

Ninety adult males divided in six equal groups were exposed to different photoperiods for 21 days. Exposures included natural light (ca 11 hr), long photoperiod (16L:8D) and short photoperiod (8L:16D). The first three groups received these exposures at room temperature (13-20 degrees C) while the remaining three at raised temperature (36-38 degrees C). Soiled bedding of the above males was introduced in the cages of unisexually housed noncyclic females and their potentiality to induce oestrus was assessed. It was noticed that the bedding of all the males proved to be a stimulus inducing oestrus in the majority of the females during the 7 day exposure. There was no significant difference in the number of females returning to oestrus following exposure to soiled bedding of different males. These results elucidate that environmental factors, especially light and temperature do not influence the production/release of the oestrus-inducing pheromone in wild mice.