Female House Mice Research Articles

Chemosignals from isolated females have antimutagenic effect in dividing the cells of bone marrow from male mice of the CBA strain

A level of X-ray induced mitotic disturbances in the cells of the bone marrow of male mice was studied under the modifying influence ofchemosignals from isolated adult female mice of the CBA line. It has been shown that the frequency of chromosomal aberrations in irradiated (4 Gr) males after exposing them for 24 hours on bedding soiled with female chemosignals is lower than in irradiated males in cages with clean bedding. The mechanisms and importance of the antimutagenic effect of female house mouse chemosignals are discussed.

Wake up and smell the conflict: odour signals in female competition.

Odour signals used in competitive and aggressive interactions between males are well studied in the context of sexual selection. By contrast, relatively little is known about comparable signals used by females, despite current interest in the evolution of female ornaments and weaponry. Available evidence suggests that odour signals are important in competitive interactions between female mammals, with reductions or reversals of male-biased sexual dimorphism in signalling where female competition is intense. Scent marking is often associated with conflict between females over access to resources or reproductive opportunities. Female scent marks may therefore provide reliable signals of competitive ability that could be used both by competitors and potential mates. Consistent with this hypothesis, we report that aggressive behaviour of female house mice is correlated with the amount of major urinary protein (MUP) excreted in their urine, a polymorphic set of proteins that are used in scent mark signalling. Under semi-natural conditions, females with high MUP output are more likely to produce offspring sired by males that have high reproductive success, and less likely to produce offspring by multiple different sires, suggesting that females with strong MUP signals are monopolized by males of particularly high quality. We conclude that odour signals are worthy of more detailed investigation as mediators of female competition.

Why do female mice mate with multiple males?

Females often show multi-male mating (MMM), but the adaptive functions are unclear. We tested whether female house mice (Mus musculus musculus) show MMM when they can choose their mates without male coercion. We released 32 females into separate enclosures where they could choose to mate with two neighboring males that were restricted to their own territories. We also tested whether females increase MMM when the available males appeared unable to exclude intruders from their territories. To manipulate territorial intrusion, we introduced scent-marked tiles from the neighboring males into males' territories, or we rearranged tiles within males' own territories as a control. Each female was tested in treatment and control conditions and we conducted paternity analyses on the 57 litters produced. We found that 46 % of litters were multiply sired, indicating that multiple paternity is common when females can choose their mates. Intrusion did not increase multiple paternity, though multiple paternity was significantly greater in the first trial when the males were virgins compared to the second trial. Since virgin male mice are highly infanticidal, this finding is consistent with the infanticide avoidance hypothesis. We also found that multiple paternity was higher when competing males showed small differences in their amount of scent marking, suggesting that females reduce MMM when they can detect differences in males' quality. Finally, multiple paternity was associated with increased litter size but only in the intrusion treatment, which suggests that the effect of multiple paternity on offspring number is dependent on male–male interactions.

A Selfish Genetic Element Influencing Longevity Correlates with Reactive Behavioural Traits in Female House Mice (Mus domesticus)

According to theory in life-history and animal personality, individuals with high fitness expectations should be risk-averse, while individuals with low fitness expectations should be more bold. In female house mice, a selfish genetic element, the t haplotype, is associated with increased longevity under natural conditions, representing an appropriate case study to investigate this recent theory empirically. Following theory, females heterozygous for the t haplotype (+/t) are hypothesised to express more reactive personality traits and be more shy, less explorative and less active compared to the shorter-lived homozygous wildtype females (+/+). As males of different haplotype do not differ in survival, no similar pattern is expected. We tested these predictions by quantifying boldness, exploration, activity, and energetic intake in both +/t and +/+ mice. +/t females, unlike +/+ ones, expressed some reactive-like personality traits: +/t females were less active, less prone to form an exploratory routine and tended to ingest less food. Taken together these results suggest that differences in animal personality may contribute to the survival advantage observed in +/t females but fail to provide full empirical support for recent theory.

Physiological adaptations to reproduction II. Mitochondrial adjustments in livers of lactating mice

Reproduction imposes significant costs and is characterized by an increased energy demand. As a consequence, individuals adjust their cellular structure and function in response to this physiological constraint. Because mitochondria are central to energy production, changes in their functional properties are likely to occur during reproduction. Such changes could cause adjustments in reactive oxygen species (ROS) production and consequently in oxidative stress levels. In this study, we investigated several mechanisms involved in energy production, including mitochondrial respiration at different steps of the electron transport system (ETS) and related the results to citrate synthase activity in the liver of non-reproductive and reproductive (two and eight pups) female house mice at peak lactation. Whereas we did not find differences between females having different litter sizes, liver mitochondria of reproductive females showed lower ETS activity and an increase in mitochondrial density when compared with the non-reproductive females. Although it is possible that these changes were due to combined processes involved in reproduction and not to the relative investment in lactation, we propose that the mitochondrial adjustment in liver might help to spare substrates and therefore energy for milk production in the mammary gland. Moreover, our results suggest that these changes lead to an increase in ROS production that subsequently upregulates antioxidant defence activity and decreases oxidative stress.

Necrophobic behavior in small mammals

Necrophobic behaviors, defined as the avoidance of dead or injured conspecifics, have been formally documented in insects and aquatic organisms. It is plausible that such avoidance has been selected for by the risks of predation and disease that are associated with the presence of cadavers, and that necrophobic behaviors may be present across a variety of taxa. We demonstrate the avoidance of a house mouse (Mus musculus) cadaver by small mammals visiting experimental food trays, and by male and female house mice in a Y-maze exploration paradigm. In addition, we present individual differences in the responses of house mice to a house mouse cadaver. Further, we propose potential applications for the study of necrophobic behavior in improving wildlife management practices and models in disease ecology.

Polyandrous females benefit by producing sons that achieve high reproductive success in a competitive environment

Females of many taxa often copulate with multiple males and incite sperm competition. On the premise that males of high genetic quality are more successful in sperm competition, it has been suggested that females may benefit from polyandry by accruing 'good genes' for their offspring. Laboratory studies have shown that multiple mating can increase female fitness through enhanced embryo viability, and have exposed how polyandry influences the evolution of the ejaculate. However, such studies often do not allow for both female mate choice and male-male competition to operate simultaneously. Here, I took house mice (Mus domesticus) from selection lines that had been evolving with (polygamous) and without (monogamous) sperm competition for 16 generations and, by placing them in free-ranging enclosures for 11 weeks, forced them to compete for access to resources and mates. Parentage analyses revealed that female reproductive success was not influenced by selection history, but there was a significant paternity bias towards males from the polygamous selection lines. Therefore, I show that female house mice benefit from polyandry by producing sons that achieve increased fitness in a semi-natural environment.

Is oxidative stress a physiological cost of reproduction? An experimental test in house mice

Investment in reproduction is costly and frequently decreases survival or future reproductive success. However, the proximate underlying causes for this are largely unknown. Oxidative stress has been suggested as a cost of reproduction and several studies have demonstrated changes in antioxidants with reproductive investment. Here, we test whether oxidative stress is a consequence of reproduction in female house mice (Mus musculus domesticus), which have extremely high energetic demands during reproduction, particularly through lactation. Assessing oxidative damage after a long period of reproductive investment, there was no evidence of increased oxidative stress, even when females were required to defend their breeding territory. Instead, in the liver, markers of oxidative damage (malonaldehyde, protein thiols and the proportion of glutathione in the oxidized form) indicated lower oxidative stress in reproducing females when compared with non-reproductive controls. Even during peak lactation, none of the markers of oxidative damage indicated higher oxidative stress than among non-reproductive females, although a positive correlation between protein oxidation and litter mass suggested that oxidative stress may increase with fecundity. Our results indicate that changes in redox status occur during reproduction in house mice, but suggest that females use mechanisms to cope with the consequences of increased energetic demands and limit oxidative stress.

EXPERIMENTAL EVOLUTION OF SPERM QUALITY VIA POSTCOPULATORY SEXUAL SELECTION IN HOUSE MICE

Individuals of many species copulate with multiple mates (polygamy). Multiple mating by females (polyandry) promotes sperm competition, which has broad implications for the evolution of the ejaculate. Multigenerational studies of polygamous insects have shown that the removal of sexual selection has profound fitness consequences for females, and can lead to an evolutionary divergence in ejaculate traits. However, the evolutionary implications of polygamous mating across successive generations have not before been demonstrated in a vertebrate. By manipulating the mating system we were able to reinstate postcopulatory sexual selection in a house mouse population that had a long history of enforced monogamy. Following eight generations of selection, we performed sperm quality assays on males from both the polygamous and monogamous selection lines. We applied a principal component analysis to summarize the variation among 12 correlated sperm traits, and found that males evolving under sperm competition had significantly larger scores on the first axis of variation, reflecting greater numbers of epididymal sperm and increased sperm motility, compared to males from lines under relaxed selection. Moreover, we found a correlated response in the size of litters born to females in lines subject to sperm competition. Thus, we present significant evidence that sperm competition has profound fitness consequences for both male and female house mice.

Effects of “Pheromone-Like” pyrazine-containing compounds on stability of genetic apparatus in bone marrow cells of the male house mouse Mus musculus L.

There was studied effect of female house mouse pheromone 2,5-dimethylpyrazine and other pyrazine-containing substances on the genetic apparatus stability of dividing bone marrow cells of male mice of the strain CBA. Differences in action of the used chemosignals are revealed. Role of the method of action on induction of analyzed mitotic aberrations is shown. Spectrum of the aberrations is analyzed. Dependence of cytogenetic activity of the used substances on their structural peculiarities and significance of the revealed effects are discussed.

Female House Mice Develop a Unique Ovarian Lesion in Colonies That Are at Maximum Population Density

Abstract. Colonies of house mice reach maximum population density in 120–180 days, irrespective of cage size and initial number of colonizing animals. Reproduction ceases because the females become aggressive and unreceptive to mating. The aggressive behavior is correlated with elevated levels of testosterone (T) and corticosterone (B) (Chapman et al., Phys Behav 64:529–533, 1998). In two of seven strains of mice, females developed ovarian lesions. The occurrence of the lesion in one strain was correlated with the age of the animal and duration of the study. In the second strain, cage size was the determining factor. Lesioned ovaries weighed significantly more than nonlesioned ovaries. The lesion consisted of accumulations of luteal membrane and organelle fragments, and other cellular debris, suggestive of incomplete and prolonged luteolysis. Electron microscopic (EM) analyses revealed the presence of deposits of permanganate-resistant congophilic amyloid fibrils in the intima and smooth muscle cells of luteal thecal arteries. Population females had thymus glands and uteri that weighed significantly less than the same organs from females housed in the breeding colony, whereas the adrenal glands from the population females weighed significantly more. It is proposed that the female aggression is due to high levels of T. It is also proposed that the high levels of B suppress the immune cells involved in normal luteolysis and contribute to the incomplete and prolonged luteolysis.

Polyandry, sperm competition, and reproductive success in mice

Previous studies have attempted to assess the reproductive benefits of polyandry in mammals but have failed to account for variation in mating frequency across experimental treatments. Recently, it has been shown that multiply sired litters are common in natural populations of house mice, suggesting that female mice are actively polyandrous and sperm competition occurs in this species. Here we show that female house mice mated to 3 males (polyandry) had greater postbirth pup survival than females mated 3 times to the same male (monandry). Remote behavioral observations revealed that copulation frequency did not differ across our experimental treatments. We discuss this result with reference to genetic benefit hypotheses for the evolution of polyandry. Furthermore, by genotyping parents and offspring in the polyandrous treatment, we assessed which male reproductive traits contributed to paternity. We found that the first principal component describing variation in 10 male reproductive variables explained a significant proportion of the variation in paternity when males were second to mate. This component was weighted predominantly by measures of sperm length, suggesting that males with short sperm may be more successful when engaging in a disfavored role of sperm competition. Key words: genetic incompatibility, intrinsic sire effects, multiple mating, offspring viability, paternity, sperm size. [Behav Ecol]

Not only mate choice matters: fitness consequences of social partner choice in female house mice

In addition to sexual selection, selection resulting from social interactions in contexts other than mating can be a potent evolutionary force. Such social selection processes are facilitated whenever individual fitness varies as a result of any form of social interactions. The choice of social partners for communal care of young is such a situation in which interactants potentially experience fitness variance. In this study, we investigated the existence and impact of female social partner choice and the potential for social selection to occur in the cooperatively breeding wild house mouse, Mus domesticus . We analysed patterns of individual associations in groups of females, and compared the reproductive behaviour of females grouped with either a preferred or a nonpreferred social partner over an experimental life span of half a year, using spatial association as a measure of preference. We predicted low reproductive competition among preferred social partners and high competition, reflected in lower reproductive success, among nonpreferred. Our results showed that female house mice displayed nonrandom preferences, and that social partner choice yielded significant fitness benefits. Females in pairs with a preferred partner had a significantly higher probability to give birth and to establish an egalitarian, cooperative relationship, resulting in higher reproductive success than females in nonpreferred pairs. This suggests that interactions among females are subject to social selection processes, driving the evolution of female traits.

Measurement of the digit lengths and the anogenital distance in mice

Measurement of the digit lengths and the anogenital distance in mice

Developmental exposure to low-dose estrogenic endocrine disruptors alters sex differences in exploration and emotional responses in mice

Estrogenic endocrine disruptors (EEDs) are naturally occurring or man-made compounds present in the environment that are able to bind to estrogen receptors and interfere with normal cellular development in target organs and tissues. There is mounting evidence that EEDs can interfere with the processes of sexual differentiation of brain and behavior in different animal models. We investigated the effects of maternal exposure to EEDs, at concentrations within the range of human exposure and not patently teratogenic, on behavioral responses of male and female house mice ( Mus musculus domesticus) before and after puberty. Pregnant dams were trained to spontaneously drink daily doses of corn oil with or without the estrogenic plastic derivative, bisphenol A (BPA 10 μg/kg), or the estrogenic insecticide methoxychlor (MXC 20 μg/kg) from gestation day 11 to postpartum day 8. Their male and female offspring were examined at different ages to examine several components of explorative and emotional behaviors in 3 experimental paradigms: a novelty test before puberty and, as adults, a free-exploratory open-field test and the elevated plus maze test. The main results are sex differences in control mice on a number of behavioral responses at both ages and in all experimental paradigms, while perinatal exposure to BPA or MXC decreased or eliminated such sex differences. The present findings are evidence of long-term consequences of developmental exposure to BPA and MXC on neurobehavioral development and suggest a differential effect of low-dose exposure to these estrogenic chemicals in males and females.

Effects of male kinship and agonistic behaviour on reproduction and odour preferences of female house mice, Mus domesticus

In gregarious species, males may wound or kill females during intermale contest competition, which directly affects females fitness. However, male–male agonistic encounters may also have more subtle effects on females by creating a stressful social environment in which females live. We examined whether male–male aggression affects female fitness and odour preference in house mice. We tested (1) whether pairs of brothers would be less likely to fight than pairs of nonbrothers; (2) whether females housed with two males that were brothers would have higher reproductive success than females housed with two males that were not brothers and (3) whether females would show a preference for the odours of brother or nonbrother pairs. Males that were brothers were less aggressive towards each other than were nonbrothers, and females housed with males that were brothers produced significantly more litters than those housed with males that were not brothers. Females did not show a preference for the odours of brothers or nonbrothers, but they did prefer odours of less aggressive pairs of males. These findings suggest that while contest competition favours fighting among males, female choice and kin selection favour tolerance.

Selective approach to a male and subsequent receptivity to mounting comprise mate‐choice behavior of female mice1

Abstract: To ensure the effectiveness of the mate‐choice behavior of female house mice (Mus domesticus), we observed them in two different situations that involved restriction of the area of movement of the male mice. In Experiment 1, we observed 12 trios consisting of two male mice and an estrous female placed in a chamber in which none of the animals was restricted during the 6‐h test. It was found that the female was more receptive to the male that had ejaculated with it first. Additionally, when the female initiated the mating event by approaching the male, the lordosis quotient was higher than that when the male initiated the mating event. In Experiment 2, a female was able to visit two males that were prevented from getting out of small boxes. As a result of the 3‐h observation of 10 cases, it was found that the females were more receptive to the dominant male. The intromission ratio of the dominant male was also higher than that of the subordinate male. The behavioral roles of female mice in mating interactions and their adaptive validity are discussed.

Exploration and risk assessment in female wild house mice ( Mus musculus musculus) and two laboratory strains

In an evolutionary prospective, it is possible that female mice have a differential perception of novel events than male mice and use a different behavioural strategy for risk assessment. However, female mice are less studied than male mice in behavioural tests of emotional reactivity. The aim of the present study was to investigate how wild-derived female house mice differ from domesticated female mice in their risk assessment strategy. A total of 46 adult female mice, 14 BALB/c, 16 C57BL/6 and 14 Wild mice were tested in the Concentric Square Field (CSF), Open Field (OF) and Elevated Plus Maze (EPM) at three consecutive days. Parameters from all three tests were categorized according to their relevance to activity, exploration, approach–avoidance and use of open areas–shelter. Principal Component Analysis (PCA-SIMCA) of the animals' behaviour in the CSF arena was performed both for females alone and in comparison with earlier findings in male mice under the same test conditions. The results clearly show that female wild mice had a higher avoidance of open areas than the laboratory strains. There was also a trend indicating differences in exploration and approach–avoidance between female Wild and the laboratory strains. The multivariate test, CSF, was able to detect differences between Wild and laboratory strains in three (exploration, approach–avoidance, open–shelter) of the four functional categories measured. Wild female mice also had a higher frequency of rearing and grooming and a lower duration in the corridors in the CSF. Clear strain differences were found between BALB and C57BL in all tests where BALB generally had higher risk assessment and lower risk taking than C57BL. No general sex differences were found, however the sex differences were greater in Wild mice compared to the laboratory strains.

Kin-preferential cooperation, dominance-dependent reproductive skew, and competition for mates in communally nesting female house mice

Little is known about the behavioural mechanisms facilitating kin-preferential communal breeding in wild house mice (Mus domesticus). We evaluated the effect of kinship and male availability on aggression, social structure and reproductive skew in groups of female mice freely interacting and reproducing in semi-natural indoor enclosures. Triplets of either sisters or non-sisters were established in enclosures provided with either one or three littermate males, which were unrelated and unfamiliar to the females. Sisters were more spatially associated and less aggressive than non-sisters, leading to higher incidences of communal breeding and reproduction. This is in agreement with theoretical considerations on kin selection in house mice. Reproductive success was highly skewed in favour of dominant females due to subordinate infertility or complete loss of first litters, which might have been caused by dominant females. In spite of this, subordinates only rarely dispersed from the enclosures, suggesting that perceived dispersal risk generally outweighed relatively reduced reproductive potentials. Aggression levels among females were significantly higher when one male was available, compared to when three males were available. We suggest that this might result from higher female-female competition for mates, due to the risk of missing fertilisation when synchronously oestrous females encounter limited numbers of males in a deme. Our results indicate that, first, communal nursing in house mice might have evolved to ‘make the best out of a bad job’ rather than to enhance offspring fitness; and, second, that female-female mate-competition might play an important role in shaping female social structure in this polygynous mammal.

Pre-reproductive alliance formation in female wild house mice ( Mus domesticus ): the effects of familiarity and age disparity

Female house mice (Mus domesticus) are known to perform communal breeding more often with kin than with non-kin partners. When mice are grouped in semi-natural enclosures, related females develop pre- reproductive alliances more frequently than unrelated ones. However, little is known about the behavioural mechanisms and the factors promoting kin preferential cooperative associations in female mice. Here we evaluate the relative importance of familiarity and age disparity on the pre-reproductive development of agonistic behaviour and spatial associations within groups of three related females, freely interacting in semi-natural indoor enclo- sures. We found that familiarity clearly promoted female alliance formation by reducing aggression and enhancing spatial cohabitation, while genetic relatedness per se did not alleviate the effects of unfamiliarity on female grouping. Older sisters clearly dominated younger ones, even if they had lower body weights, or if they had to confront two allied littermate sisters. Hence, our findings corroborate previous findings on familiarity as a proxy for kin-preferential alliance formation in female mice. More- over, we observed a strong impact of age stratification on female aggression-mediated dominance development. We suggest that this age effect could be expected from a queuing-for-reproduction view of younger house mouse females.