Intermittent stimulation and acceleration of puberty by urinary chemosignals in female mice (Mus musculus domesticus)

A sequence of 17 experiments was used to test the effects of intermittent stimulation with urinary chemosignals on the age of puberty in young female mice. The three chemosignals tested all accelerate the age of sexual maturation: urine from adult males, urine from females in estrus, and urine from females that are pregnant or lactating. The basic technique involved presenting the prepubertal females with 'Nestlets' on which the urine was placed. The 'Nestlets' were placed in the cages of the test females for a 15-min period, removed for a variable period, and then replaced in the cage for 15 min. In this manner it was possible to vary the number of exposures, the total length of exposure, and the total time period over which the exposures occurred. Control procedures, involving exposures of young females to cotton squares with water rather than urine placed upon them, resulted in no alterations in puberty relative to untreated females. For mice exposed to the urine-treated cotton squares, acceleration of puberty occurred with less total stimulus-exposure time when the stimulus was presented in short exposures over a number of hours than in previous investigations when the exposure to the urinary chemosignal occurred in a single block of time of one or two hours. For each of the three acceleratory chemosignals, there was a diminution of acceleratory effect when the ratio of total stimulus-exposure time to total exposure time grew smaller. This diminution was more pronounced for urine from pregnant or lactating females than for urine from males or from females in estrus.(ABSTRACT TRUNCATED AT 250 WORDS)     

Oxytocin inhibits infanticide in female house mice (Mus domesticus)

Between 60 and 90% of female house mice spontaneously kill unrelated young. A previous report indicated that subcutaneous administration of oxytocin significantly reduced the frequency of infanticide by virgin and pregnant females. However, in this study a distinction could not be made between an action of oxytocin on the CNS versus a secondary effect such as an enhanced release of prolactin by oxytocin. In the current experiment, oxytocin administered intracerebroventricularly was equally as effective at inhibiting infanticide as sc oxytocin. There was no difference in the effectiveness of oxytocin between groups of infanticidal females that were gonadally intact, ovariectomized, or estrogen treated. Pretreatment of infanticidal females with the prolactin inhibitors, bromocriptine and cysteamine, was also without effect on the ability of oxytocin to inhibit infanticide. Last, prolactin-inhibiting drugs had no significant effect on spontaneous parenting behavior by female mice. These data suggest that oxytocin acts directly on the CNS to alter behavior toward pups and that prolactin may not play a role in the maternal behavior of the house mouse.     

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.     

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.     

Communal nesting and communal nursing in house mice,Mus musculus domesticus

The functional significance of communal nesting and nursing is poorly understood. Female house mice often communally nest, and within these communal nests females appear to indiscriminately nurse all pups, a rare trait for any mammal. In this study, the hypothesis that communal nesting provides protection from conspecific infanticide was tested and supported in semi-natural populations of house mice. Conspecific infanticide in single-mother nests (69%, N = 412) was twice that in communal nests (33%, N = 508). Because this major benefit of communal nesting does not require communal nursing, direct benefits to communal nursing itself were tested. Most proposed benefits should result in heavier weaning weights, but no differences were found between communal and single nests in the semi-natural populations. If communal nursing is to be avoided in communal nests, dams must recognize their own pups. Retrieval tests conducted in the laboratory produced equivocal results. Dams discriminated between pups that differed in age, but not between their own and other age-matched pups. The major survival advantage of communal nesting, coupled with the failure to find nutritional advantages for communally nursed pups, supports a recent suggestion that communal nursing is an unavoidable consequence of communal nesting. This hypothesis is further strengthened by data indicating that communal nesting partners tend to be kin, thereby providing inclusive fitness benefits to communal nursing. Although costs of communal nursing were proposed and tested, no such costs were found. We also show from 15 observations of infanticide that all classes of adults (territorial and non-territorial males, pregnant and non-pregnant females) are infanticidal. These observations are in conflict with previous laboratory studies.     

Mitochondrial DNA variation in house mice, Mus domesticus (Rutty)

This article summarizes knowledge of house mouse diversity based on restriction analysis of mtDNA from 202 individuals representing 83 localities in Europe, North Africa, the Middle East, and the Americas. It begins by describing the variation among 34 newly collected European mice and relating the 15 new types of mtDNA found in them to the 37 types known from previous work. None of the new types represent deep new branches in the tree. Moreover, the order of branching in the tree reinforces the view that mice north of the Alps have southern origins. Two possible time scales are under consideration for the process of colonization of north-western Europe. According to one hypothesis, which assumes that the mtDNA clock in mice ticks at the standard mammalian rate, commensal mice colonized Europe north of the Alps roughly 30 000–70 000 years ago, perhaps in concert with the spread of anatomically modern Homo sapiens . Another hypothesis, which requires accelerated mtDNA evolution in mice, would have the colonization take place 5000–6000 years ago, or even more recently, following the spread of agriculture. The study also shows that mtDNAs closely resembling those M. domesticus mtDNAs that introgressed into the Danish and Swedish populations of M. musculus are widespread in M. domesticus populations of the region near the hybrid zone between these two species in Germany.     

Effects of voluntary activity and genetic selection on aerobic capacity in house mice (Mus domesticus)

Swallow, John G., Theodore Garland, Jr., Patrick A. Carter,Wen-Zhi Zhan, and Gary C. Sieck. Effects of voluntary activity andgenetic selection on aerobic capacity in house mice(Mus domesticus). J. Appl. Physiol. 84(1): 69-76, 1998.An animal model was developed to study effects on components ofexercise physiology of both "nature" (10 generations of geneticselection for high voluntary activity on running wheels) and"nurture" (7-8 wk of access or no access to running wheels,beginning at weaning). At the end of the experiment, mice from bothwheel-access groups were significantly lighter in body mass than micefrom sedentary groups. Within the wheel-access group, a statisticallysignificant, negative relationship existed between activity and finalbody mass. In measurements of maximum oxygen consumption during forcedtreadmill exercise (O_{2 max}), mice withwheel access were significantly more cooperative than sedentary mice;however, trial quality was not a significant predictor of individualvariation in O_{2 max}.Nested two-way analysis of covariance demonstrated that both geneticselection history and access to wheels had significant positive effects on O_{2 max}.A 12% difference inO_{2 max} existedbetween wheel-access selected mice, which had the highestmass-correctedO_{2 max}, andsedentary control mice, which had the lowest. The respiratory exchangeratio at O_{2 max} wasalso significantly lower in the wheel-access group. Our results suggestthe existence of a possible genetic correlation between voluntaryactivity levels (behavior) and aerobic capacity (physiology).

     

Effects of voluntary activity and genetic selection on muscle metabolic capacities in house mice Mus domesticus.

Selective breeding is an important tool in behavioral genetics and evolutionary physiology, but it has rarely been applied to the study of exercise physiology. We are using artificial selection for increased wheel-running behavior to study the correlated evolution of locomotor activity and physiological determinants of exercise capacity in house mice. We studied enzyme activities and their response to voluntary wheel running in mixed hindlimb muscles of mice from generation 14, at which time individuals from selected lines ran more than twice as many revolutions per day as those from control (unselected) lines. Beginning at weaning and for 8 wk, we housed mice from each of four replicate selected lines and four replicate control lines with access to wheels that were free to rotate (wheel-access group) or locked (sedentary group). Among sedentary animals, mice from selected lines did not exhibit a general increase in aerobic capacities: no mitochondrial [except pyruvate dehydrogenase (PDH)] or glycolytic enzyme activity was significantly (P < 0.05) higher than in control mice. Sedentary mice from the selected lines exhibited a trend for higher muscle aerobic capacities, as indicated by higher levels of mitochondrial (cytochrome-c oxidase, carnitine palmitoyltransferase, citrate synthase, and PDH) and glycolytic (hexokinase and phosphofructokinase) enzymes, with concomitant lower anaerobic capacities, as indicated by lactate dehydrogenase (especially in male mice). Consistent with previous studies of endurance training in rats via voluntary wheel running or forced treadmill exercise, cytochrome-c oxidase, citrate synthase, and carnitine palmitoyltransferase activity increased in the wheel-access groups for both genders; hexokinase also increased in both genders. Some enzymes showed gender-specific responses: PDH and lactate dehydrogenase increased in wheel-access male but not female mice, and glycogen phosphorylase decreased in female but not in male mice. Two-way analysis of covariance revealed significant interactions between line type and activity group; for several enzymes, activities showed greater changes in mice from selected lines, presumably because such mice ran more revolutions per day and at greater velocities. Thus genetic selection for increased voluntary wheel running did not reduce the capability of muscle aerobic capacity to respond to training.     

The frequency of multiple paternity suggests that sperm competition is common in house mice (Mus domesticus)

Sexual selection is an important force driving the evolution of morphological and genetic traits. To determine the importance of male-male, postcopulatory sexual selection in natural populations of house mice, we estimated the frequency of multiple paternity, defined as the frequency with which a pregnant female carried a litter fertilized by more than one male. By genotyping eight microsatellite markers from 1095 mice, we found evidence of multiple paternity from 33 of 143. Evidence for multiple paternity was especially strong for 29 of these litters. Multiple paternity was significantly more common in higher-density vs. lower-density populations. Any estimate of multiple paternity will be an underestimate of the frequency of multiple mating, defined as the frequency with which a female mates with more than a single male during a single oestrus cycle. We used computer simulations to estimate the frequency of multiple mating, incorporating observed reductions in heterozygosity and levels of allele sharing among mother and father. These simulations indicated that multiple mating is common, occurring in at least 20% of all oestrus cycles. The exact estimate depends on the competitive skew among males, a parameter for which we currently have no data from natural populations. This study suggests that sperm competition is an important aspect of postcopulatory sexual selection in house mice.     

The population ecology of house mice (Mus domesticus) on the Isle of May, Scotland

The colonizing ability, catholic habitat utilization and wide distribution of house mice ( Mus domesticus , Rutty) are indicators of their ecological resilience. Numerous studies have been made of commensal, caged and free-living mouse populations though few have assessed the relative importance of physiological and genetical components of adaptability in a simple ecosystem. This paper reports such findings, derived from live-trapping which formed part of an inter-disciplinary study of adaptability in a feral population of house mice living on a small Scottish island (57 ha).
The population size ranged from450–3250 animals. A high proportion of mice showed homerange tenacity, though15–20% shifted their range during winter. This 'churning' of the population is consistent with the island population forming an effectively panmictic unit rather than fragmented demes. The breeding season, survival of individuals and change in population size related to patterns of gross climatic variation (temperature and rainfall) so that rates of reproduction and survival were lowest in cold, wet conditions. Thermoregulatory adjustment of the mice to lowered ambient temperatures and its contribution to overwinter survival are discussed. Genetical monomorphism of May Island mice is discussed in relation to their biological performance compared with other populations, especially that of the ecologically comparable Skokholm Island (Wales).     

Antimutagenic effect of chemosignals from isolated female house mouse on male germ cells (Mus musculus L.)

The influence of chemosignals from isolated mature females of the CBA strain on level of spontaneous and radiation-induced meiotic disturbances in spermatocytes I of males of the same strain was studied. Using an ana-telophase method, 24-hour exposure of males to soiled bedding containing isolated females’ chemosignals was shown to lead to a significantly lower frequency of chromosomal aberrations and other meiotic disturbances in spermatocytes I as compared to males kept on clean bedding. The same effect of female chemosignals was found in the germ cells of irradiated males (4 Gr). The mechanisms and importance of the revealed antimutagenic effect of mouse female chemosignals on the male reproductive cells in the reproduction process are discussed.     

Use of the MHC for mate choice in wild house mice (Mus domesticus)

The mechanisms maintaining natural diversity at the major histocompatibility complex (MHC) are not well understood. To increase knowledge of one potential mechanism, I examined the use of MHC genes for mate choice by wild house mice in a controlled laboratory setting. Three rearing groups of wild test mice were produced: non‐fostered control mice, mice fostered into families of an inbred laboratory mouse strain, and mice fostered into families of a second, MHC‐congenic mouse strain. Mature test mice were given a choice of two opposite‐sex stimulus mice from the two MHC‐congenic strains used for fostering, and were scored for several measures of preference. The results were non‐significant in general, but females of two rearing groups spent significantly more time with mice of one MHC‐type, and in most rearing groups, mice tended to spend more time with this same MHC‐type. Other results showed that male test mice ejaculated indiscriminantly and that female wild mice mated to ejaculation more often in longer length trials, but showed no significant preferences. In this study, fostering seemed to have little or no effect on MHC‐based mate preferences of wild house mice, and wild mice did not appear to be using the MHC to avoid inbreeding. However, some wild female mice used the MHC to choose potential mates. This revised version was published online in July 2006 with corrections to the Cover Date.     

Serological survey of virus infection among wild house mice (Mus domesticus) in the UK

The serological prevalence of 13 murine viruses was surveyed among 103 wild-caught and 51 captive-bred house mice (Mus domesticus), originating from several trapping locations in northwest England, using blood samples obtained during routine health screening of an established wild mouse colony. A high proportion of recently caught wild mice were seropositive for mouse hepatitis virus (86%), mouse cytomegalovirus (79%), mouse thymic virus (78%), mouse adenovirus (68%), mouse parvovirus (59%) and minute virus of mice (41%). Seroprevalences of lymphocytic choriomeningitis virus (LCMV), orthopoxvirus, reovirus-3 and murid herpesvirus 4 (MuHV-4, also called murine gamma-herpesvirus [MHV-68]) were low (3-13%), and no animals were seropositive to Sendai virus, pneumonia virus or polyomavirus. Seroprevalence in wild-caught animals that had been in captivity for over six months was generally consistent with the range found in recently caught wild animals, while seroprevalence was generally much lower in captive-bred mice despite no attempt to prevent viral spread. A notable exception to this was LCMV, which appeared to have spread efficiently through the captive population (both captive-bred and wild-caught animals). Given the known viral life cycles in laboratory mice, it appears that viral persistence in the host was an important contributing factor in the spread of infection in captivity.     

Intracranial androgenic and estrogenic stimulation of male-typical behaviors in house mice (Mus domesticus).

Two experiments in house mice (Mus domesticus) examined the neural sites at which steroid hormones activate the following male-typical behaviors: 70 kHz ultrasonic mating vocalizations in response to stimulus females or their urine, urinary marking in response to stimulus males or stimulus females, mounting of estrous females, and intermale aggression. In the first experiment, four groups of castrated males received bilateral intracranial implants of testosterone (T) into either the septum (SEPTUM), medial preoptic area (MPO), anterior hypothalamus (AHA), or ventromedial hypothalamus (VMH). Two control groups received subcutaneous silastic capsules of T (TSIL) or empty silastic capsules (BSIL). The TSIL males performed all behaviors at male-typical levels while the BSIL males were unresponsive. MPO males emitted ultrasonic mating vocalizations at high levels while few vocalizations were seen in males of the other brain implant groups. The VMH, AHA, and MPO males urine marked at higher levels than the BSIL males but did not exhibit the high levels of the TSIL males. Mounting was observed only in MPO and TSIL males. Aggression was rare in males from any of the brain implant groups. In the second experiment, the hormone activity of the implants was increased by using testosterone propionate (TP) or a 50% mixture of estradiol (E2) and cholesterol. The six groups were SEPTUMTP, SEPTUME2, MPOTP, MPOE2, TPSIL, and BSIL. The TPSIL males performed all behaviors at male-typical levels while the BSIL males were unresponsive. TP was effective at restoring vocalizations and urine marking only when placed in the MPO; however, E2 was effective at both sites. Again aggression and mounting were less evident in the brain implanted males. In conclusion, implants of T or TP were effective in restoring ultrasonic mating vocalization when placed into the MPO. MPO implants of T and TP were also effective in stimulating urine marking, although VMH and AHA implants also showed some effectiveness. The restorative effects of E2 were not localized which is probably related to the greater hormonal activity of this treatment. Comparisons of the properties of the various brain implants to restore more than one behavior were discussed.     

Structural complexity of territories: preference, use of space and defence in commensal house mice, Mus domesticus

Previous studies suggest the physical structure of a habitat has profound effects on intraspecific competition and spacing behaviour among small mammals. We compared habitat preferences and the exploratory behaviour and aggressive territorial defence of male house mice in three types of enclosure differing only in their degree of structural complexity. Each enclosure contained a nestbox placed in one corner, a central food hopper and 10 house bricks. The bricks were either placed around the outer walls (open enclosures), lined up across the middle (wall enclosures) or scattered separately across the floor (complex enclosures). In pairwise choice tests, mice showed a strong preference for wall or complex enclosures over open enclosures but no preference between wall and complex enclosures. They were more active throughout the enclosure with complex structuring and stayed near the side walls in open enclosures. Residents in open enclosures initially showed a lower rate of attack and duration of pursuit when faced with an intruder but not when faced with a second intruder. In complex enclosures, nearly all encounters ended because the residents continued pursuit but lost track of the intruder. This occurred in only half of intruder pursuits in open and wall enclosures. Our results suggest that mice prefer areas containing physical structure because this provides a degree of protection from predators but territories with complex physical structuring appear to be much more difficult to defend. Complex areas may thus support a higher density of mice than open areas or those with more simply aligned physical structuring. Copyright 2000 The Association for the Study of Animal Behaviour.     

Balance hypothesis of action of socially significant volatile chemosignals on reactivity of chromosome machinery of the bone marrow dividing cells in the house mouse Mus domesticus L

Volatile chemosignals released by female CBA laboratory mice have been shown to produce action of different direction, depending on conditions of performance of experiment, on chromosome machinery of bone marrow cells in syngenic adult males. Thus, chemosignals secreted into environment by isolated adult females decrease frequency of mitotic disturbances in bone marrow dividing cells in male recipients as compared with spontaneous level in control animals. At the same time, 2,5-dimethylpyrazine - pheronome released only by high density caged females - increases frequency of mitotic disturbances. Preliminary 24-h-long action of chemosignals of isolated females decreases effect of the subsequent action of 2,5-dimethylpyrazine, although the level of disturbances exceeds that in control animals. The simultaneous action of used chemosignals neutralizes completely the 2,5-dimethylpyrazine action, the frequency of mitotic disturbances being not different from that after chemosignals of isolated females. The hypothesis is put forward about dependence of the revealed cytogenetic effects in male recipients on zoosocial conditions of maintenance of female donors of chemocommunication signals.     

The effect of sub-lethal doses of bromadiolone on the breeding performance of house mice (Mus domesticus)

Both laboratory and field strains of Mus were exposed to wheat containing 0.0001% bromadiolone under laboratory and outdoor conditions, respectively. While both strains readily consumed the poisoned wheat, ad libitum sub-lethal doses of this anticoagulant equating to between 20% and 70% of the acute ld₅₀ per feed had little apparent effect on the breeding performance of these mice. The implications of these findings are discussed with respect to the use of anticoagulants as pesticides.