Urine marking in populations of wild house mice Mus domesticus Rutty. III. Communication between the sexes

Dynamic changes to signal allocation rules in response to variable social environments in house mice

Urine marking is central to mouse social behavior. Males use depletable and costly urine marks in intrasexual competition and mate attraction. We investigate how males alter signaling decisions across variable social landscapes using thermal imaging to capture spatiotemporal marking data. Thermal recording reveals fine-scale adjustments in urinary motor patterns in response to competition and social odors. Males demonstrate striking winner-loser effects in scent mark allocation effort and timing. Competitive experience primes temporal features of marking and modulates responses to scent familiarity. Males adjust signaling effort, mark latency, and marking rhythm, depending on the scent identities in the environment. Notably, recent contest outcome affects how males respond to familiar and unfamiliar urine. Winners increase marking effort toward unfamiliar relative to familiar male scents, whereas losers reduce marking effort to unfamiliar but increase to familiar rival scents. All males adjust their scent mark timing after a contest regardless of fight outcome, and deposit marks in more rapid bursts during marking bouts. In contrast to this dynamism, initial signal investment predicts aspects of scent marking days later, revealing the possibility of alternative marking strategies among competitive males. These data show that mice flexibly update their signaling decisions in response to changing social landscapes.

Transmission of food preference via faeces in male and female house mice: Who is a good provider of food cues?

The social transmission of food preference (STFP) is a phenomenon that allows rodents to use food information perceived from their conspecifics to guide their own food choices. This social information can be collected via olfactory cues, during direct social interactions, or indirectly, via faeces left in the environment by individuals. Although reducing the risks associated with a social confrontation, faeces also convey different types of information about traits and states of individuals which could affect the indirect STFP. Here, we evaluated in the house mouse, Mus musculus domesticus, which conspecifics could be good providers of food cues for indirect STFP. Our results indicated that female mice acquire an indirect STFP from faeces of adult females, familiar or not and from faeces of adult unfamiliar males. On the contrary, males do not establish an indirect STFP from faeces of males, whether they are familiar or not, nor from those of unfamiliar females. Indirect STFP was however effective in males when the faeces were those of an unfamiliar juvenile male. A prior habituation to the odour of an unfamiliar female allowed the establishment of indirect STFP in males. Conversely, the presence of faeces of another adult male during the presentation of faeces of an accustomed female precluded the acquisition of indirect STFP in males. This study suggested that in the context of the indirect STFP, females prioritize socio-olfactory information relative to food, whereas food cues were not priority information for males. Under these conditions, females appear to be the best vectors for disseminating food information within the population. These results are discussed according to the socio-spatial organization of the species.

Identification and Field Testing of Volatile Components in the Sex Attractant Pheromone Blend of Female House Mice

Recently, it was reported (i) that the sex pheromone blend of male house mice, Mus musculus, comprises not only volatile components (3,4-dehydro-exo-brevicomin; 2-sec-butyl-4,5-dihydrothiazole) but also a component of low volatility (the sex steroid testosterone), and (ii) that the sex steroids progesterone and estradiol are sex pheromone components of female house mice. Here we tested the hypothesis that the sex attractant pheromone blend of female mice, analogous to that of male mice, also comprises volatile pheromone components. Analyzing by GC-MS the head space volatiles of bedding soiled with urine and feces of laboratory-kept females and males revealed three candidate pheromone components (CPCs) that were adult female-specific: butyric acid, 2-methyl butyric acid and 4-heptanone. In a two-choice laboratory experiment, adult males spent significantly more time in the treatment chamber baited with both the synthetic steroids (progesterone, estradiol) and the synthetic CPCs than in the paired control chamber baited only with the synthetic steroids. In field experiments, trap boxes baited with both the CPCs and the steroids captured 6.7-times more adult males and 4.7-times more juvenile males than trap boxes baited with the steroids alone. Conversely, trap boxes baited with both the CPCs and the steroids captured 4.3-times more adult males and 2.7-fold fewer adult females than trap boxes baited with the CPCs alone. In combination, these data support the conclusion that butyric acid, 2-methyl butyric acid and 4-heptanone are part of the sex attractant pheromone of female house mice. With progesterone and estradiol being pheromone components of both female brown rats, Rattus norvegicus, and female house mice, these three volatile components could impart specificity to the sexual communication system of house mice, brown rats and possibly other rodent species.

Void spot assay procedural optimization and software for rapid and objective quantification of rodent voiding function, including overlapping urine spots

Mouse urinary behavior is quantifiable and is used to pinpoint mechanisms of voiding dysfunction and evaluate potential human therapies. Approaches to evaluate mouse urinary function vary widely among laboratories, however, complicating cross-study comparisons. Here, we describe development and multi-institutional validation of a new tool for objective, consistent, and rapid analysis of mouse void spot assay (VSA) data. Void Whizzard is a freely available software plugin for FIJI (a distribution of ImageJ) that facilitates VSA image batch processing and data extraction. We describe its features, demonstrate them by evaluating how specific VSA method parameters influence voiding behavior, and establish Void Whizzard as an expedited method for VSA analysis. This study includes control and obese diabetic mice as models of urinary dysfunction to increase rigor and ensure relevance across distinct voiding patterns. In particular, we show that Void Whizzard is an effective tool for quantifying nonconcentric overlapping void spots, which commonly confound analyses. We also show that mouse genetics are consistently more influential than assay design parameters when it comes to VSA outcomes. None of the following procedural modifications to reduce overlapping spots masked these genetic-related differences: reduction of VSA testing duration, water access during the assay period, placement of a wire mesh cage bottom on top of or elevated over the filter paper, treatment of mesh with a hydrophobic spray, and size of wire mesh opening. The Void Whizzard software and rigorous validation of VSA methodological parameters described here advance the goal of standardizing mouse urinary phenotyping for comprehensive urinary phenome analyses.

Odor Communication and Mate Choice in Rodents

This paper details how chemical communication is affected by ecological challenges such as finding mates. I list several conditions that affect the decision to attract mates, the decision to respond to the signals of potential mates and how the response depends on context. These mate-choice decisions and their outcomes will depend on the life history constraints placed on individuals such as their fecundity, sex, lifespan, opportunities to mate in the future and age at senescence. Consequently, the sender's decision to scent mark or self-groom as well as the receiver's choice of response represents a tradeoff between the current costs of the participant's own survival and future reproduction against that of reproducing now. The decision to scent nark and the response to the scent mark of opposite-sex conspecifics should maximize the fitness of the participants in that context.

Species differences in urine scent-marking and counter-marking in Peromyscus

Species comparisons indicate that scent-marking may differ as a function of mating system and co-housing with the opposite sex ("pairing"). We previously demonstrated that pairing may decrease male solicitation to unfamiliar females in the monogamous Peromyscus californicus but not in the non-monogamous P. leucopus. Whether urine scent-marking of females changes following pairing and whether scent-marking of paired males varies in response to scent-marks of their cagemate versus those of an unfamiliar female has not been examined. Therefore, we tested P. californicus and P. leucopus for within and between species differences in urine scent-marking of: 1) paired and non-paired females in an unscented arena, and 2) paired males in response to their female cagemate's or an unfamiliar female's scent-marks (counter-marking). Consistent with previous findings, P. californicus of both sexes deposited more urine scent-marks and covered greater surface area than P. leucopus. In both species, female scent-marking did not differ according to pairing status and male counter-marking did not differ in response to the scent-marks of their female cagemate versus an unfamiliar female. More females of both species and more P. leucopus, but not P. californicus, males scent-marked more around the perimeter than centrally. Potential explanations for these findings are discussed.

Sources of variance within and among young men in concentrations of 17β-estradiol and testosterone in axillary perspiration

The most potent estrogen, 17β-estradiol (E₂), and its precursor, testosterone (T), play critical roles in mammalian reproductive processes. Evidence indicates that these steroids are present in bioactive form in the excretions of many male mammals. It has been demonstrated that small lipophilic steroids such as E₂ can be absorbed by proximate females from male excretions, arriving in the uterus, brain, and other organs where there are estrogen receptors. We took repeated samples of axillary perspiration from men aged 20-30years during vigorous exercise. Both steroids were consistently measurable, with concentrations that ranged from values comparable to those in facial perspiration and urine of both men and women to values that greatly exceeded concentrations observed in any other substrate of men and women. Inter-individual variance in axillary E₂ was positively correlated with the extent of intimate experience with women, as assessed by a questionnaire, but unrelated to subjective measures of stress, exercise habits, or phytoestrogen content of diet. In addition, higher levels of axillary E₂ were observed in participants when samples were collected by a female (as compared to a male) experimenter. These data are concordant with an hypothesis that male excretion of sex steroids could exert pro-reproductive influences on proximate females.

Sex steroids as pheromones in mammals: the exceptional role of estradiol

This article is part of a Special Issue (Chemosignals and Reproduction). Whether from endogenous or exogenous sources, 17β-estradiol (E2) has very powerful influences over mammalian female reproductive physiology and behavior. Given its highly lipophilic nature and low molecular mass, E2 readily enters excretions and can be absorbed from exogenous sources via nasal, cutaneous, and other modes of exposure. Indeed, systemic injection of tritiated estradiol ((3)H-E2) into a male mouse or bat has been shown to produce significant levels of radioactivity in the reproductive tissues and brain of cohabiting female conspecifics. Bioactive E2 and other steroids are naturally found in male mouse urine and other excretions, and males actively direct their urine at proximate females. Very low doses of E2 can mimic the Bruce effect (disruption of peri-implantation pregnancy by novel males), the Vandenbergh effect (early reproductive maturation induced by novel males), and male-induced estrus and ovulation. Males' capacities to induce the Bruce and Vandenbergh effects can both be diminished by manipulations that reduce their urinary E2. Uterine dynamics during the Bruce and Vandenbergh effects are consistent with the actions of E2. Collectively, these data demonstrate a critical role of male-sourced E2 in these major mammalian pheromonal effects.

Scent-marking behaviour and social dynamics in a wild population of Eurasian lynx Lynx lynx

Scent-marking is widespread among mammals and has been observed in many felid species. Although the behaviour is well-described, little is known about its function in wild felid populations. We investigated patterns of scent-marking and its role in intra- and intersexual communication among resident and non-resident Eurasian lynx Lynx lynx by observing interactions among wild lynx at natural marking sites by means of infrared camera traps. Marking activity of resident animals showed a peak during the mating season and was lowest during the time when females gave birth and lactated. Both sexes scent-marked, but male lynx visited marking sites much more often than females and marked relatively more often when visiting a site. Most visits to marking sites were by residents but we also observed scent-marking by non-residents. Juveniles were never observed marking. We found no evidence of lynx regularly renewing scent-marks after a certain 'expiry date' but the presence of a strange scent-mark triggered over-marking. Males responded similarly to the presence of another individual's scent-mark, irrespective of whether it was the top- or the underlying scent-mark in a mixture of scent-marks they encountered. Our results suggest that marking sites could serve as 'chemical bulletin boards', where male lynx advertise their presence and gain information on ownership relationships in a given area. Females placed their urine marks on top of the ones left by resident males, but further studies are needed to explain the functions of over-marking in females.

Scent marking increases male reproductive success in wild house mice

Scent marking is often assumed to be a secondary sexual trait that increases males' mating and reproductive success, although direct evidence for this hypothesis is lacking. We conducted a study with wild-derived house mice, Mus musculus musculus, to test whether scent marking increases males' reproductive success when females can freely choose between two territorial males. We also experimentally manipulated males' competitive scent marking by exchanging scent-marked tiles between the neighbouring males' territories (intrusion treatment) or relocating males' tiles within their own territory (control). Experimental animals were tested twice and we examined whether individual males were consistent in their marking. We found that males marked more in the intrusion treatment than controls and more at shared territorial borders than elsewhere. We found high day-to-day variation in most individuals' scent marking, and yet the sum of individuals' scent marking was consistent over time and across different social conditions. Genetic paternity analyses revealed that males' scent marking significantly increased their reproductive success in both the intrusion treatment and the controls. Surprisingly, however, female social preference was not positively correlated with male scent marking. These results provide direct evidence that scent marking increases males' reproductive success when females can choose their mates, even though it did not increase females' social preferences.

Chemosignals and hormones in the neural control of mammalian sexual behavior

Males and females of most mammalian species depend on chemosignals to find, attract and evaluate mates and, in most cases, these appetitive sexual behaviors are strongly modulated by activational and organizational effects of sex steroids. The neural circuit underlying chemosensory-mediated pre- and peri-copulatory behavior involves the medial amygdala (MA), the bed nucleus of the stria terminalis (BNST), medial preoptic area (MPOA) and ventromedial hypothalamus (VMH), each area being subdivided into interconnected chemoreceptive and hormone-sensitive zones. For males, MA-BNST connections mediate chemoinvestigation whereas the MA-MPOA pathway regulates copulatory initiation. For females, MA-MPOA/BNST connections also control aspects of precopulatory behavior whereas MA-VMH projections control both precopulatory and copulatory behavior. Significant gaps in understanding remain, including the role of VMH in male behavior and MPOA in female appetitive behavior, the function of cortical amygdala, the underlying chemical architecture of this circuit and sex differences in hormonal and neurochemical regulation of precopulatory behavior.

Urine scent marking (USM): a novel test for depressive-like behavior and a predictor of stress resiliency in mice

Decreased interest in pleasurable stimuli including social withdrawal and reduced libido are some of the key symptomatic criteria for major depression, and thus assays that measure social and sexual behavior in rodents may be highly appropriate for modeling depressive states. Here we present a novel approach for validating rodent models of depression by assessing male urine scent marking (USM) made in consequence to a spot of urine from a proestrous female. USM is an ethologically important form of sexual communication expressed by males to attract females. The expression of this behavior is highly sensitive and adaptive to environmental cues and social status. We hypothesized that male USM behavior offers a naturalistic measure of social motivation that can be used to evaluate hedonic behaviors relevant to the study of mood disorders. We demonstrated that 1) adult male mice displayed a strong preference for marking proestrous female urine with a high degree of specificity, 2) exposure to chronic social defeat profoundly decreased USM whereas exposure to environmental enrichment increased USM, 3) the standard antidepressant fluoxetine reversed declines in USM induced by social defeat, 4) USM behavior closely correlated with other hedonic measures, and 5) USM scores in non-stressed mice predicted behavioral outcomes after defeat exposure such that mice displaying high preference for marking female urine prior to social defeat showed behavioral resiliency after social defeat. The findings indicate that the USM test is a sensitive, validated measure of psychosocial stress effects that has high predictive value for examination of stress resiliency and vulnerability and their neurobiological substrates.

Chemosignals, hormones and mammalian reproduction

Many mammalian species use chemosignals to coordinate reproduction by altering the physiology and behavior of both sexes. Chemosignals prime reproductive physiology so that individuals become sexually mature and active at times when mating is most probable and suppress it when it is not. Once in reproductive condition, odors produced and deposited by both males and females are used to find and select individuals for mating. The production, dissemination and appropriate responses to these cues are modulated heavily by organizational and activational effects of gonadal sex steroids and thereby intrinsically link chemical communication to the broader reproductive context. Many compounds have been identified as "pheromones" but very few have met the expectations of that term: a unitary, species-typical substance that is both necessary and sufficient for an experience-independent behavioral or physiological response. In contrast, most responses to chemosignals are dependent or heavily modulated by experience, either in adulthood or during development. Mechanistically, chemosignals are perceived by both main and accessory (vomeronasal) olfactory systems with the importance of each system tied strongly to the nature of the stimulus rather than to the response. In the central nervous system, the vast majority of responses to chemosignals are mediated by cortical and medial amygdala connections with hypothalamic and other forebrain structures. Despite the importance of chemosignals in mammals, many details of chemical communication differ even among closely related species and defy clear categorization. Although generating much research and public interest, strong evidence for the existence of a robust chemical communication among humans is lacking.

Oestradiol transmission from males to females in the context of the Bruce and Vandenbergh effects in mice (Mus musculus)

Male mice actively direct their urine at nearby females, and this urine reliably contains unconjugated oestradiol (E2) and other steroids. Giving inseminated females minute doses of exogenous E2, either systemically or intranasally, can cause failure of blastocyst implantation. Giving juvenile females minute doses of exogenous E2 promotes measures of reproductive maturity such as uterine mass. Here we show that tritium-labelled E2 (3H-E2) can be traced from injection into novel male mice to tissues of cohabiting inseminated and juvenile females. We show the presence of 3H-E2 in male excretions, transmission to the circulation of females and arrival in the female reproductive tract. In males, 3H-E2 given systemically was readily found in reproductive tissues and was especially abundant in bladder urine. In females, 3H-E2 was found to enter the system via both nasal and percutaneous routes, and was measurable in the uterus and other tissues. As supraoptimal E2 levels can both interfere with blastocyst implantation in inseminated females and promote uterine growth in juvenile females, we suggest that absorption of male-excreted E2 can account for major aspects of the Bruce and Vandenbergh effects.

Communication impairments in mice lacking Shank1: reduced levels of ultrasonic vocalizations and scent marking behavior

Autism is a neurodevelopmental disorder with a strong genetic component. Core symptoms are abnormal reciprocal social interactions, qualitative impairments in communication, and repetitive and stereotyped patterns of behavior with restricted interests. Candidate genes for autism include the SHANK gene family, as mutations in SHANK2 and SHANK3 have been detected in several autistic individuals. SHANK genes code for a family of scaffolding proteins located in the postsynaptic density of excitatory synapses. To test the hypothesis that a mutation in SHANK1 contributes to the symptoms of autism, we evaluated Shank1(-/-) null mutant mice for behavioral phenotypes with relevance to autism, focusing on social communication. Ultrasonic vocalizations and the deposition of scent marks appear to be two major modes of mouse communication. Our findings revealed evidence for low levels of ultrasonic vocalizations and scent marks in Shank1(-/-) mice as compared to wildtype Shank1(+/+) littermate controls. Shank1(-/-) pups emitted fewer vocalizations than Shank1(+/+) pups when isolated from mother and littermates. In adulthood, genotype affected scent marking behavior in the presence of female urinary pheromones. Adult Shank1(-/-) males deposited fewer scent marks in proximity to female urine than Shank1(+/+) males. Call emission in response to female urinary pheromones also differed between genotypes. Shank1(+/+) mice changed their calling pattern dependent on previous female interactions, while Shank1(-/-) mice were unaffected, indicating a failure of Shank1(-/-) males to learn from a social experience. The reduced levels of ultrasonic vocalizations and scent marking behavior in Shank1(-/-) mice are consistent with a phenotype relevant to social communication deficits in autism.

The level of major urinary proteins is socially regulated in wild Mus musculus musculus

Major urinary proteins (MUPs) are highly polymorphic proteins that have been shown to perform several important functions in the chemical communication of the house mouse, Mus musculus. Production of these proteins in C57Bl/6 females is cyclic, reaching the maximum just before the beginning of estrus. Social environment is an important factor that increases MUP production in both sexes. We examined responsiveness of MUP production to social stimuli in wild mice, Mus musculus musculus. The direction of change of MUP production in males depended on the sex of the stimulus animal. Males up-regulated MUP production when caged with a female, but down-regulated MUP production when caged with a male. Down-regulation was more pronounced in males that were defeated in a male-male encounter. Females responded to a male's presence with a decrease in MUP production. We conclude that social modulation of MUP production is specific and, in coordination with other mechanisms, facilitates adjustment of the animal's odor profile to different social contexts. Our results also suggest that in males, MUPs may play an important role in advertizing the male's quality to females. Furthermore, we highlight the importance of analyzing data corrected with creatinine, which show MUP production on the (post)translational level as well as raw data (non-corrected with creatinine), which represent actual concentrations of MUPs in the urine.

Reduced scent marking and ultrasonic vocalizations in the BTBR T+tf/J mouse model of autism

Qualitative impairments in communication, such as delayed language and poor interactive communication skills, are fundamental to the diagnosis of autism. Investigations into social communication in adult BTBR T+tf/J (BTBR) mice are needed to determine whether this inbred strain incorporates phenotypes relevant to the second diagnostic symptom of autism, communication deficits, along with its strong behavioral phenotypes relevant to the first and third diagnostic symptoms, impairments in social interactions and high levels of repetitive behavior. The aim of the present study was to simultaneously measure female urine-elicited scent marking and ultrasonic vocalizations in adult male BTBR mice, in comparison with a standard control strain with high sociability, C57BL/6J (B6), for the assessment of a potential communication deficit in BTBR. Adult male BTBR mice displayed lower scent marking and minimal ultrasonic vocalization responses to female urine obtained from both B6 and BTBR females. Lower scent marking and ultrasonic vocalizations in a social setting by BTBR, as compared with B6, are consistent with the well-replicated social deficits in this inbred mouse strain. Our findings support the interpretation that BTBR incorporate communication deficits, and suggest that scent marking and ultrasonic vocalizations offer promising measures of interest in social cues that may be widely applicable to investigations of mouse models of autism.

Female urine-induced male mice ultrasonic vocalizations, but not scent-marking, is modulated by social experience

Despite the evidence for a communicative function of rodent scent marks and ultrasonic vocalizations, relatively little is known about the impact of social factors on these two forms of communication. Here, we tested the effects of two important social factors, prior exposure to a female and freshness of female urine, on male scent marks and ultrasonic vocalizations elicited by female urine. We also asked whether a recently reported strain difference between the highly social strain C57BL/6J (B6) and the mouse model of autism BTBR T+tf/J (BTBR) herein is specifically seen in response to female urine or also detectable in response to male urine traces. Results show that the emission of female urine-elicited ultrasonic vocalizations was dependent on previous female experience, while scent-marking behavior was not affected. A positive correlation was detected between scent-marking behavior and ultrasonic calling in the most biologically relevant context, male mice exposed to fresh female urine after female experience. Correlations were less prominent or missing in less biologically relevant contexts, e.g. in male mice exposed to fresh female urine without previous female experience, indicating that previous female experience is affecting both the emission of female urine-elicited ultrasonic vocalizations and the correlation between olfactory and acoustic communication. The strain difference in scent-marking behavior and ultrasonic calling between B6 and BTBR appears to be specific to female urine-elicited behavior as it was not seen in response to male urine traces, highlighting the relevance of the social context in which mouse communication is evaluated.

Olfactory experience affects the response of meadow voles to the opposite-sex scent donor of mixed-sex over-marks

Scent marking and over-marking are important forms of communication between the sexes for many terrestrial mammals. Over the course of three experiments, we determined whether the amount of time individuals investigate the scent marks of opposite-sex conspecifics is affected by four days of olfactory experience with those conspecifics. In experiment 1, female meadow voles, Microtus pennsylvanicus, spent more time investigating the scent mark of the novel male conspecific than that of the familiar male donor, whereas male voles spent similar amounts of time investigating the scent mark of the familiar female and a novel female conspecific. In experiment 2, voles were exposed to a mixed-sex over-mark in which subjects did not have four days of olfactory experience with either the top-scent donor or the bottom-scent donor. During the test phase, male and female voles spent more time investigating the scent mark of the opposite-sex conspecific that provided the top-scent mark than that of a novel, opposite-sex conspecific. Male and female voles spent similar amounts of time investigating the scent mark of the bottom-scent donor and that of a novel opposite-sex conspecific. In experiment 3, voles were exposed to a mixed-sex over-mark that contained the scent mark of an opposite-sex conspecific with which they had four days of olfactory experience. During the test phase, male voles spent more time investigating the mark of the familiar, top-scent female than the scent mark of a novel female donor but spent similar amounts of time investigating the mark of the familiar, bottom-scent female and that of a novel female donor. In contrast, female voles spent more time investigating the mark of a novel male donor than that of either the familiar, top-scent male or that of the familiar, bottom-scent male. The sex differences in the responses of voles to scent marks and mixed-sex over-marks are discussed in relation to the natural history and non-monogamous mating system of meadow voles.

Identification of testosterone-dependent volatile compounds and proteins in the preputial gland of rat Rattus norvegicus

Preputial gland is one of the best known and most odour-producing organs in many non-primate mammals. It is generally believed that the development of this gland and functions are regulated by testosterone. To substantiate this point, the present study was aimed to evaluate the testosterone-dependent volatile compounds and proteins in the preputial gland of rat adopting castration and testosterone supplementation. The results revealed that four compounds, geranyl linalool isomer, oxirane, farnesol and lanosterol, are testosterone-dependent. Similarly, a low molecular mass protein with molecular weight 18kDa, supposed to be a pheromone carrier, also is shown to be testosterone-dependent. This study leads to the conclusion that testosterone-dependent compounds and sex-associated protein are present in the preputial gland of rat which may act as a sex pheromone and pheromone carrier, respectively.

Excretion and binding of tritium-labelled oestradiol in mice (Mus musculus): implications for the Bruce effect

Male mouse urine contains 17beta-oestradiol (E(2)) and other steroids. Given that males actively direct urine at proximate females and intrauterine implantation of blastocysts is vulnerable to minute amounts of exogenous oestrogens, males' capacity to disrupt early pregnancy could be mediated by steroids in their urine. When male mice were implanted with osmotic pumps containing tritium-labelled E(2) ((3)H-E(2)) or injected i.p. with (3)H-E(2), radioactivity was reliably detected in their urine. Following intranasal administration of (3)H-E(2) to inseminated females, radioactivity was detected in diverse tissue samples, with there being significantly more in reproductive tissues than in brain tissues. When urine was taken from males injected with (3)H-E(2), and then intranasally administered to inseminated females, radioactivity was detected in the uterus, olfactory bulbs, and mesencephalon and diencephalon (MC+DC). When inseminated and ovariectomised females were perfused at the point of killing to remove blood from tissues, more radioactivity was detected in the uterus than in muscle, olfactory bulbs, MC+DC and cerebral cortex. Pre-treatment with unlabelled E(2) significantly reduced the uptake of (3)H-E(2) in the uterus. Taken with evidence that males deliver their urine to the nasal area of females, these results indicate that male urinary E(2) arrives in tissues, including the uterus, where it could lead to the disruption of blastocyst implantation.

Age affects over-marking of opposite-sex scent marks in meadow voles, Microtus pennsylvanicus

Models of age-related effects on behavior predict that among short-lived species younger adults are more attractive and attracted to opposite-sex conspecifics than are older adults, whereas the converse is predicted for long-lived species. Although most studies of age-related effects on behavior support these predictions, they are not supported by many studies of scent marking, a behavior used in mate attraction. Over-marking, a form of scent marking, is a tactic used by many terrestrial mammals to convey information about themselves to opposite-sex conspecifics. The present study tested the hypothesis that the age of meadow voles, Microtus pennsylvanicus; a microtine rodent, affects their over- and scent marking behaviors when they encounter the marks of opposite-sex conspecifics. Sex differences existed in the over-marking behavior of adult voles among the three different age groups that were tested. Male voles that were 5-7 mo-old and 10-12 mo-old over-marked a higher proportion of the marks of females than did 2-3 mo-old male voles. Female voles that were 2-3 mo-old, 5-7 mo-old, and 10-12 mo-old over-marked a similar number of marks deposited by male voles. Overall, the data were not consistent with models predicting the behavior of short-lived animals such as rodents when they encounter the opposite sex. The differences in over-marking displayed by older and younger adult male voles may be associated with life history tradeoffs, the likelihood that they will encounter sexually receptive females, and being selected as mates.

Receiving behaviour is sensitive to risks from eavesdropping predators

Conspicuous signals may attract both intended receivers as well as unintended receivers such as predators. However, signalling individuals are not the only ones at risk when communicating, as the intended receiver may encounter eavesdropping predators that are attracted to the same signals. Here, we show that the house mouse (Mus domesticus) behaviourally responds to social signals (scents) as though receiving carries a risk of predation. We presented mice with their own scents (low social benefit to receiving) and those from an unknown "intruder" (high social benefit to receiving) under high (cat urine added) and low (water added) perceived predation risk. Mice traded-off the potential social benefits of receiving a signal against the costs of potential predator encounter. Receiving rates of both social signals (own and intruder) were high under low predation risk. Mice reduced receiving of both social signals when predation risk was increased; however, the effect was greater for their own low value scent than for the high social value intruder scent. Notably, rates of signalling did not vary with the level of perceived predation risk. Our findings suggest that mice traded-off the potential social benefits of receiving a signal (scent mark) against the costs of potential predator encounter. We suggest that, for some species, the costs of communication are borne more by the receivers than the signallers, and that the influence of risks to receivers on the design of communication systems may have been underestimated.

Exposure to developing females induces polyuria, polydipsia, and altered urinary levels of creatinine, 17beta-estradiol, and testosterone in adult male mice (Mus musculus)

Novel male mice can accelerate reproductive maturation in proximal developing females, an effect mediated by the chemistry of the males' urine. Exogenous estrogens can similarly accelerate female sexual development. In Experiment 1, adult male mice were housed across wire grid from either empty compartments or those containing post-weanling females. Proximity of females caused males to urinate more, progressively over days of exposure, with most urination directed towards females' compartments. Male urine collected after 5 days in these conditions was analyzed by enzyme immunoassay for 17beta-estradiol, testosterone, and creatinine. Urinary creatinine of isolated males significantly exceeded that of female-exposed males. Unadjusted urinary steroids also trended toward higher levels in isolates, but creatinine-adjusted estradiol and testosterone of female-exposed males significantly exceeded that of isolated males. In Experiment 2, measurement of water consumption indicated significantly greater drinking by female-exposed as opposed to isolated males. In Experiment 3, males were housed in isolation or beside post-weanling intact (sham-operated) females, ovariectomized females, or intact (sham-operated) males. Male water consumption was elevated in all conditions involving social contact. Urinary creatinine was significantly lower in female-exposed males compared to isolated controls, while unadjusted testosterone was significantly lower in males in all social conditions. Again, creatinine-adjusted estradiol in female-exposed males significantly exceeded that of isolates. These data indicate that adult males drink and urinate more, have more dilute urine, and have a higher ratio of estradiol to creatinine when they are near developing females. These dynamics increase females' exposure to urinary steroids and other urinary constituents that can hasten sexual maturity.

Preputialectomised and intact adult male mice exhibit an elevated urinary ratio of oestradiol to creatinine in the presence of developing females, whilst promoting uterine and ovarian growth of these females

Exposure to novel adult males and their urine can hasten the onset of sexual maturity in female mice. Some evidence implicates chemosignals from males’ preputial glands, while other evidence suggests that male urinary steroids, especially 17β-oestradiol, contribute to this effect. The present experiment was designed to determine whether preputial gland removal would influence the capacity of males to accelerate female sexual development, and to measure male urinary oestradiol and testosterone in the presence or absence of these glands. Juvenile females aged 28 days were housed for two weeks in isolation or underneath two outbred males that had undergone preputialectomy or sham surgery. Urine samples were collected non-invasively from males that were isolated or exposed to females, then assayed for oestradiol, testosterone and creatinine. Combined uterine and ovarian mass from females sacrificed at 43 days of age was increased by exposure to males, regardless of whether or not these males had been preputialectomised. Male urinary creatinine was reduced by exposure to developing females. Creatinine-adjusted oestradiol and testosterone were significantly greater in female-exposed than in isolated males, in both preputialectomised and intact males. These data suggest that the preputials are not necessary for the capacity of males to hasten female uterine and ovarian growth. As exogenous oestrogens can promote uterine growth and other parameters of female reproductive maturation, oestradiol in males’ urine may contribute to earlier sexual maturity in male-exposed females.

Freezing urine reduces its efficacy for eliciting ultrasonic vocalizations from male mice

Studies on chemosensory communication generally rely on using samples of emanations that have been frozen for convenience, and assume that freezing has no detrimental effects. Female urine triggers courtship ultrasonic vocalizations (USVs) in male mice, and in this study, we examined whether freezing urine affects males' USV responses. We used wild-derived house mice (Mus musculus musculus), and recorded males' USVs after being presented samples of fresh versus frozen urine. We found that males emitted significantly fewer USVs when presented with frozen versus fresh urine, and furthermore, males were no longer able to discriminate the scent of familiar versus unfamiliar females after samples were frozen. Our findings indicate that freezing alters the bioactivity of urinary compounds both by reducing its potential to elicit behavioral responses from receivers (male courtship USVs) and eliminating important information about senders (familiarity). Freezing may denature the major urinary proteins (MUPs) released in rodent urine that play an important role in chemical communication. Our results raise concerns about the negative results of studies utilizing frozen samples for studying chemical signals.

Signalling components of the house mouse mate recognition system

Subspecies-specific mate recognition may represent significant barrier to gene flow between diverged genomes potentially leading to speciation. In the house mouse, assortative mating involves the coevolution of several signals and receptors. We compared signalling ability of bedding material, faeces, urine, saliva, salivary androgen binding proteins (ABP) and combinations of urine with saliva and urine with ABP in mate choice in two wild-derived inbred strains (one of Mus musculus musculus and one of Mus musculus domesticus origin). We observed high levels of variation in assortative preferences between the two strains and sexes. The strongest preferences were observed in M. m. musculus-derived individuals in tests where urine was present either alone or as part of a composite signal target. M. m. domesticus-derived mice displayed strain-specific preferences for faeces. Saliva was the least preferred stimulus in both strains and sexes. No effect of two-compound cues was detected. We conclude that there is divergence across both the stimulus and preference parts of the recognition system for both house mouse strains. Of the tested stimuli, those that have the capacity to carry a signal for extended periods under natural conditions (such as urine and faeces) seem to be the most important substances in strain-specific recognition.

Scent marking behavior as an odorant communication in mice

In rodents, where chemical signals play a particularly important role in determining intraspecies interactions including social dominance and intersexual relationships, various studies have shown that behavior is sensitive to conspecific odor cues. Mice use urinary scent marks for communication with individual conspecifics in many social contexts. Urinary scent involves genetic information about individuals such as species, sex, and individual identity as well as metabolic information such as social dominance, and reproductive and health status, which are mediated by chemical proteins in scent marks including the major histocompatibility complex and the major urinary proteins. The odor of the predator which can be considered to be a threatening signal for the prey also modulate mouse behavior in which scent marking is suppressed in response to the cat odor exposure in mice. These odorant chemicals are detected and recognized through two olfactory bulbs, the role of which in detection of chemosignals with biological relevant appears to be differential, but partly overlapped. Mice deposit scent marks toward conspecifics to maintain their social relationships, and inhibit scent marking in a context where natural predator, cat odor is contained. This suppression of scent marking is long-lasting (for at least 7 days) and context-dependent, while the odorant signaling to conspecifics tends to appear frequently (over 24h but less than 7 days intervals) depending on the familiarity of each signal-recipient. It has been discussed that scent marking is a communicative behavior associated with territoriality toward conspecifics, indicating that the social signaling within species are sensitive to predator odor cues in terms of vulnerability to predation risk.

Olfactory responses of neotropical short-tailed singing mice, Scotinomys teguina, to odors of the mid-ventral sebaceous gland: discrimination of conspecifics, gender, and female reproductive condition

We examined the olfactory communication of the Neotropical short-tailed singing mouse, Scotinomys teguina, by investigating whether S. teguina responded to odors produced by the mid-ventral sebaceous gland of conspecifics. Females spent significantly more time investigating male odor than an odorless stimulus or a female odor. Males spent significantly more time investigating female odor than an odorless stimulus, but not that of a male odor. This latter result does not seem to be explained by differences in age or sexual experience of test subjects, but may be influenced by reproductive condition of the female odor donor. Male S. teguina spent significantly more time (1) investigating and (2) in total proximity to odors of estrous than non-estrous females. Males spent more time (1) investigating and (2) in total proximity to odors of males than non-estrous females. Finally, given the choice between odor of males vs proestrous females, males showed no preference. Thus, the mid-ventral gland in S. teguina seems to convey information about conspecifics, sex, and female reproductive condition. Male odor, compared with proestrous female odor, is equally interesting to males, suggesting that the gland also plays an important role in male-male communication. Sexual dimorphism in the size of the gland and in the amount of secretion produced by the gland may be related to either male-male competition or female choice.