Aggression and commensalism in house mouse: a comparative study across Europe and the near east

Sentinels in the shadows: Exploring Toxoplasma gondii and other Sarcocystidae parasites in synanthropic rodents and their public health implications

Synanthropic rodents play a crucial role in maintaining the life cycle of Toxoplasma gondii in anthropized regions and can serve as indicators of environmental oocyst contamination. This investigation aimed to explore the occurrence of T. gondii infection within synanthropic rodent populations using a molecular diagnostic technique targeting the 18S rDNA gene, which is generic for Coccidia, with subsequent specific PCR confirmation. We examined 97 brown rats (Rattus norvegicus), 67 black rats (R. rattus), 47 house mice (Mus musculus), and 1 common shrew (Sorex araneus). PCR tests were conducted on the brain, heart, and tongue tissues. PCR tested positive in at least one of the examined tissues in 26 R. norvegicus (26.8%), 13 R. rattus (19.4%), and 13 M. musculus (27.6%). Sequencing comparisons by BLAST allowed us to identify four different species of cyst-forming Apicomplexa. In particular, T. gondii DNA was detected in 13 (6.1%) rodents, Hammondia hammondi (including H. hammondi-like organisms) in 36 (17%) subjects, Besnoitia sp. (in two cases identified as B. besnoiti) in 8 (3.7%), and Sarcocystis gigantea in two (0.94%). Rodents from peri-urban and urban environments can act as indicators of environmental contamination by oocysts of apicomplexan parasites with cats as definitive hosts, such as T. gondii, H. hammondi, and S. gigantea, the latter of which has never been previously recorded in rodents. Moreover, the presence of B. besnoiti, a parasite with an unidentified definitive host in Europe, sheds light on the potential role of these hosts as infection sentinels.

Competitive ability is a fast-evolving trait between house mouse populations (Mus musculus domesticus)

BACKGROUND

House mice are commensal animals with a nearly global distribution, structured into well differentiated local populations. Besides genetic differences between the populations, they have also diverged behaviorally over time, whereby it remains open how fast general behavioral characteristics can change. Here we study the competitive potential of two very recently separated populations of the Western house mouse (Mus musculus domesticus) by using two different approaches-one under controlled cage conditions, the other under more natural conditions in enclosures mimicking a secondary encounter condition.

RESULTS

We observe a clear bias in the competitive ability towards one of the populations for both tests. The measured behavioral bias is also reflected in the number of hybrid offspring produced in the enclosures.

CONCLUSION

Our data suggest that key behavioral characteristics with a direct influence on relative fitness can quickly change during the evolution of populations. It seems possible that the colonization situation in Western Europe, with a rapid spread of the mice after their arrival, would have favored more competitive populations at the expansion front. The study shows the possible impact of behavioral changes on the evolution of populations.

Amylin-Calcitonin receptor signaling in the medial preoptic area mediates affiliative social behaviors in female mice

Social animals actively engage in contact with conspecifics and experience stress upon isolation. However, the neural mechanisms coordinating the sensing and seeking of social contacts are unclear. Here we report that amylin-calcitonin receptor (Calcr) signaling in the medial preoptic area (MPOA) mediates affiliative social contacts among adult female mice. Isolation of females from free social interactions first induces active contact-seeking, then depressive-like behavior, concurrent with a loss of Amylin mRNA expression in the MPOA. Reunion with peers induces physical contacts, activates both amylin- and Calcr-expressing neurons, and leads to a recovery of Amylin mRNA expression. Chemogenetic activation of amylin neurons increases and molecular knockdown of either amylin or Calcr attenuates contact-seeking behavior, respectively. Our data provide evidence in support of a previously postulated origin of social affiliation in mammals.

Distribution of commensal rodents in some shops of three districts in Malakand region, Pakistan

Using wire mesh live traps distribution pattern of the Rattus rattus and Mus musculus in different shops of three districts of Malakand region, Pakistan were recorded from September 2014 to October 2015. Over all 103 rodents (Rattus rattus 86 and Mus musculus 17) were caught during in 0.04 trap success (2448 trap nights). Regression of daily captures on cumulative captures revealed an estimate of 103 rodents from all the sampled structures with an average of 3.55 rodents per shop. R. rattus; 83.4% of captures were numerically dominant in almost all types of shops sampled, and were significantly different than Mus musculus; 16.5% of captures. Both species were found together in some shops while they were mostly trapped from the separate shops. Male rodents outnumbered the females.

Distribution of commensal rodents in rain-fed and irrigated areas of Swat district, Khyber Pakhtunkhwa, Pakistan

Distribution pattern and relative abundance of the agricultural rodent pests of rain-fed and irrigated areas of district Swat Khyber Pakhtunkhwa, Pakistan were recorded from April 2011 to November 2013 using wire mesh live traps. A total of 350 rodents (269 Rattus rattus and 81 Mus musculus) were captured under 2268 trap nights (trap success: 0.15). Regression of daily captures on cumulative captures revealed an estimate of 350 rodents from all the sampled structures with an average of 21.8 rodents per crop field. House rats (R. rattus; 76.8% of captures) were numerically dominant in almost all types of agricultural fields, and were significantly different from the mice (Mus musculus; 23.1% of captures). Both species were found together in some fields. The sex ratio revealed that males outnumbered the females in both of the reported species.

Ontogeny of social hierarchy in two European house mouse subspecies and difference in the social rank of dispersing males

In social species such as house mouse, being dominant is vital. Determination of dominance may start early in life and vary during ontogeny. We asked whether pre-pubertal and adolescent behaviour predicts the rank a male mouse finally obtains. Moreover, we asked how dominant vs. subordinate adults differ in exploration and propensity to emigrate. We studied fraternal pairs as the simple social units, from weaning to full-grown adulthood. By utilizing two mouse subspecies known to differ in many behavioural traits, we take into account any potential subspecific idiosyncrasies. We did not find any significant effect of future social status on any behavioural type displayed before adulthood, but the subspecies themselves differ in behaviours prevailing in particular ontogeny phases. While musculus males start as more pro-social, they later became significantly more passive. Conversely, domesticus are slightly less passive at the beginning but significantly more proactive close to adulthood and rapidly establishing hierarchy through overt conflicts. We found no difference in exploration between ranks, however, domesticus males were significantly more active in an unknown area than musculus. Most importantly, while dominant domesticus males seem to be more prone to emigration, in musculus it was the subordinate males who left base significantly more often. This is consistent with extended contests of musculus males over dominance found in this study as well as with differences in endocrinological changes we have reported previously.

On the ground and in the heights: Does exploratory activity differ in commensal and non-commensal spiny mice?

Human settlements represent a specific environment where commensal animals are exposed to different selective pressures than their wild-living conspecifics. Despite the importance of commensal rodents for human health and economy, little is known about how a transition to a commensal way of life changes the behaviour of the animals. We tested twelve populations of spiny mice (Acomys spp.) in two open field-type tests - a vertical test and a hole board test. In the vertical test, a wire mesh for climbing was offered to spiny mice. We used a multipopulation approach using two commensal and ten non-commensal spiny mouse populations to account for inter-population variability. We aimed to investigate whether there are differences in behaviour of commensal and non-commensal populations with special regard to their exploratory activity both on the ground and on the wire mesh. We found that all non-commensal populations behaved similarly despite their long separate evolutionary histories. Contrary, the commensal populations were less exploratory on the ground in both tests. We concluded that this change was associated with their transition to commensalism. This shows that selective pressures of the commensal environment are able to induce noticeable changes in behaviour after a very short evolutionary time.

Ectoparasites burden of House mouse (Mus musculus linnaeus, 1758) from Hai'l region, Kingdom of Saudi Arabia

The House mice (Mus musculus Linnaeus, 1758), play an important role in the transmission of diseases, both in humans and livestock, through ectoparasite carried on their feces, urine and hair remnants. The purpose of this study was to investigate the ectoparasites infestation, as well as their quantitative and qualitative abundance and, prevalence in the house mice captured from Hai’l region, Kingdom of Saudi Arabia (KSA). Parasitological investigations were performed on 70 house mice trapped during 2012–2013 from two localities (Hai’l City residential area and Al-Khitah agricultural farm habitats in Hai’l region). Captured mice were identified as males (34.3% and 48.6%) and females (65.7% and 51.4%) from the residential and agricultural farm habitats, respectively. The findings of the study showed that the sex ratio of the mice found in different habitats did not influence the level of ectoparasite infestation (P > 0.05). Therefore, we combined only sex-wise samples for each habitat and isolated habitats treated separately for our subsequent analyses. A total of 514 ectoparasites individuals belong to four species were recovered from the mice, which included 339 of flea (Xenopsylla cheopis Rothschild, 1903), 39 of sucking lice (Polyplax spinulosa Burmeister, 1835), 37 of sucking lice Polyplax serrata Burmeister, 1839), and 99 of mite species (Laelaps echidninus Berlese, 1887).

The presence of zoonotic parasites indicates that Mus musculus as a reservoir, might represent a danger to the public health particularly in the two sampled areas. Results also suggest an increasingly need for further studies to assess the role of the ectoparasites of house mice and their possible involvment in transmission of diseases among these areas.

Sperm quality, aggressiveness and generation turnover may facilitate unidirectional Y chromosome introgression across the European house mouse hybrid zone

The widespread and locally massive introgression of Y chromosomes of the eastern house mouse (Mus musculus musculus) into the range of the western subspecies (M. m. domesticus) in Central Europe calls for an explanation of its underlying mechanisms. Given the paternal inheritance pattern, obvious candidates for traits mediating the introgression are characters associated with sperm quantity and quality. We can also expect traits such as size, aggression or the length of generation cycles to facilitate the spread. We have created two consomic strains carrying the non-recombining region of the Y chromosome of the opposite subspecies, allowing us to study introgression in both directions, something impossible in nature due to the unidirectionality of introgression. We analyzed several traits potentially related to male fitness. Transmission of the domesticus Y onto the musculus background had negative effects on all studied traits. Likewise, domesticus males possessing the musculus Y had, on average, smaller body and testes and lower sperm count than the parental strain. However, the same consomic males tended to produce less- dissociated sperm heads, to win more dyadic encounters, and to have shorter generation cycles than pure domesticus males. These data suggest that the domesticus Y is disadvantageous on the musculus background, while introgression in the opposite direction can confer a recognizable, though not always significant, selective advantage. Our results are thus congruent with the unidirectional musculus → domesticus Y chromosome introgression in Central Europe. In addition to some previous studies, they show this to be a multifaceted phenomenon demanding a multidisciplinary approach.

Home ranges, sex ratio and recruitment of the multimammate rat (Mastomys natalensis) in semi-arid areas in Tanzania

Investigation of home ranges, sex ratio and recruitment of the multimammate rat (Mastomys natalensis) in semi-arid areas of Tanzania was conducted in maize and fallow fields using the capture-mark-release (CMR) technique. The aim of this study was to generate useful data for the management of M. natalensis. The relative home range size of M. natalensis was significantly higher during the wet [544 m2 ± 25 standard error (SE)] than during the dry (447 m2 ± 18 SE) season, in males (521 m2 ± 23 SE) than in females (450 m2 ± 17 SE) and in adults (576 m2 ± 34 SE) than in juveniles (459 m2 ± 16 SE). However, there were no significant differences between habitats. Sex ratio was not significantly different (p = 0.44) between habitats. Recruitment was significantly higher (p = 0.000) in maize fields (mean = 0.43) than in fallow land (mean = 0.32) and differed significantly over time (p < 0.0001) with the highest recruitment recorded from April to July and the lowest from October to December. Management strategies should focus on managing rodents inhabiting maize fields using methods that affect their recruitment in order to reduce the population increase of M. natalensis.

Animal conflicts in diploid populations with sexual reproduction

The classical, monomorphic, evolutionary games analyze competition among phenotypes while implicitly assuming monomorphic transmission of phenotypic attributes to successive generations. The recently formulated polymorphic evolutionary game theory (PEGT), which adds the underlying genetics and sexual reproduction to evolutionary games, has the potential to revolutionize game theoretical modeling of co-evolutionary processes. In this paper, I apply PEGT methods to the analysis of animal conflicts - the oldest, and one of the best-developed areas of evolutionary game modeling. Overall, the polymorphic results are consistent with the sequential assessment hypothesis. However, beyond the specific, the results indicate the need for a degree of caution applied to the existing evolutionary stability results - as the polymorphic analysis shows that monomorphic ESS can be destabilized by sexual recombination. Finally, due to the novelty of the analytical approach, I make a particular emphasis on methodology: in particular, demonstrating how to combine generation of pertinent phenotypes with genetic plausibility considerations in the design of PEGT models.

A longitudinal study of phenotypic changes in early domestication of house mice

Similar phenotypic changes occur across many species as a result of domestication, e.g. in pigmentation and snout size. Experimental studies of domestication have concentrated on intense and directed selection regimes, while conditions that approximate the commensal and indirect interactions with humans have not been explored. We examine long-term data on a free-living population of wild house mice that have been indirectly selected for tameness by regular exposure to humans. In the course of a decade, this mouse population exhibited significantly increased occurrence of white patches of fur and decreased head length. These phenotypic changes fit to the predictions of the 'domestication syndrome'.

Attenuated Chemosensory Responsiveness of the Grueneberg Ganglion in Mouse Pups at Warm Temperatures

Neurons of the Grueneberg ganglion (GG) in the anterior nasal region of mice respond to a small set of odorous compounds, including given dimethylpyrazines present in mouse urine. Consequently, mouse pups living in murine colonies are presumably commonly exposed to such GG-activating substances. Since stimulation of the GG elicits alarm and stress reactions in mice, the question arises whether such a GG activation potentially inducing stress could be reduced when pups might rather feel secure in the presence of their mother. Being together with their warmth-giving dam, mouse pups experience a nest temperature of ∼35 °C. Therefore, we hypothesized that such a warm temperature may attenuate the responses of GG neurons to dimethylpyrazines. Monitoring the expression of the activity marker c-Fos, GG responses to dimethylpyrazines were significantly lower in pups exposed to these substances at 35 °C compared to exposure at 30 °C. By contrast, dimethylpyrazine-induced responses of neurons in the main olfactory epithelium were not diminished at 35 °C in comparison to 30 °C. The attenuated chemosensory responses of GG neurons at 35 °C coincided with a reduced dimethylpyrazine-evoked activation of the glomeruli in the olfactory bulb innervated by GG neurons. The reduction in dimethylpyrazine-evoked GG responses by warm temperatures was positively correlated with exposure time, suggesting that warm temperatures might enhance desensitization processes in GG neurons. In summary, the findings indicate that warm temperatures similar to those in mouse nests in the presence of the dam attenuate GG activation by colony-derived odorants.

Olfactory contacts mediate plasticity in male aggression with variable male density

Males typically adjust their reproductive strategies based on the perceived density and relative abilities of nearby competitors. In high-density populations, repeated encounters facilitate reliable, learned associations between individuals and their relative competitive abilities. In contrast, opportunities to form such associations are limited when densities are low or in flux, increasing the risk that individuals will unintentionally engage in potentially costly interactions with higher-quality or aggressive opponents. To maximize their fitness, individuals in low-density and fluctuating populations therefore need a general way to assess their current social environment, and thus their relative competitive ability. Here, we investigate how olfactory social signals (scent marks) might perform this function. We manipulated the perceived social environment of isolated, male house mice ( Mus domesticus ) via their periodic contact with scent marks from 3 or 9 male conspecifics, or a control of no scents, over 15 days. We then paired them with an unknown opponent and examined how the diversity of recent scent contact mediated their behavior towards dominant or subordinate opponents. There was an overall pattern for increasing scent diversity to significantly reduce male mice’s aggression (tail rattling and lunging) towards their opponents, and also their willingness to engage in reciprocal investigation. Such cautiousness was not indicative of perceived subordinance, however; the diversity of recent scent contact did not affect mice’s investigation of their opponent’s scents, and some measures of aggression were greater when mice faced dominant opponents. These results suggest that house mice can use scent signals to assess their current social environment in the absence of physical interactions, modifying their behavior in ways that are predicted to reduce their risks of injury when the likelihood of encountering unknown opponents increases.

Shaking the myth: Body mass, aggression, steroid hormones, and social dominance in wild house mouse

In social mammals, the position of a male in the group's hierarchy strongly affects his reproductive success. Since a high social rank is often gained through competition with other males, selection should favour bigger males over smaller ones. We may therefore predict faster growth and/or delayed sexual maturity in dominant males. Likewise, dominants should have higher levels of testosterone, hormone important in many aspects of male dominance. Less obvious is the relationship between dominance and levels of corticosterone but generally higher concentrations are expected in subordinate individuals. We studied body growth, sexual maturation and endocrinal changes in males of two house mouse subspecies, raised in fraternal pairs. Since Mus musculus domesticus is the subspecies which dominates mutual encounters with Mus musculus musculus we predicted higher growth rate, delayed puberty and aggression, and higher testosterone and corticosterone levels in domesticus males compared to musculus. In all comparisons, no differences were found between dominant and subordinate musculus brothers. On the other hand, in M. m. domesticus, dominant males revealed a different growth trajectory and lower corticosterone levels than subordinate males but not delayed puberty and higher testosterone concentrations, thus contradicting our predictions. In inter-subspecific comparisons, musculus males matured earlier but became aggressive at the same time as domesticus males. The musculus testosterone ontogeny suggests that social positions in this subspecies remain unfixed for an extended period and that the increasing levels probably reflect prolonged hierarchy contests. It appears that the ontogeny of behaviour and physiological traits diverge cryptically between the two subspecies.

The ecological impacts of commensal species: black rats, Rattus rattus, at the urban–bushland interface

Exotic species have had devastating impacts worldwide and are a major threat to native wildlife. Human commensal species (hereafter commensals) are a special class of exotic species that live largely off the resources associated with human activity. The encroachment of commensals from an urban area into surrounding bushland has been frequently overlooked as an important component of urban impacts, even though human-commensals are common to many urban regions globally. In this review, we present theoretical and empirical evidence for the processes and outcomes occurring when exotic commensal species encroach into native bushland. Specifically we ask when, how and why exotic commensal species encroach into bushland, what determines whether they establish, and what are the ecological consequences. We focus on the black rat, Rattus rattus, arguably the archetypal commensal species with a cosmopolitan distribution and the greatest potential for ecological damage of all the commensal rodents. We expect that the processes that we outline apply to other commensal species more broadly. We argue that commensals are in fact natives of the urban milieu and only become alien when they encroach into peri-urban bushland. We propose that the mechanisms of this encroachment will be different from those of other, non-commensal exotic species because urban areas act as dispersal hubs to overcome many of the barriers of invasion that other exotic species face. We suggest that resource supplementation by urban areas creates a great potential for promoting encroachment, invasion as well as impact. However, biotic and abiotic barriers to invasion are still relevant for commensals, highlighting the need to maintain the integrity of ecosystems and wildlife populations in urban edges so as to prevent commensal incursion. We examine how commensal black rats affect wildlife via three fundamental mechanisms, namely, predation, disease transfer and competition for resources, and also consider their possible positive impacts acting as functional replacements for lost natives. We conclude the review with an outline of research priorities and future directions that are essential for progressing our understanding of the ecology of commensal species.

The costs and benefits of flexibility as an expression of behavioural plasticity: a primate perspective

Traditional neo-Darwinism ascribes geographical variation in morphology or in behaviour to varying selection on local genotypes. However, mobile and long-lived organisms cannot achieve local adaptation this way, leading to a renewed interest in plasticity. I examined geographical variation in orang-utan subsistence and social behaviour, and found this to be largely owing to behavioural plasticity, here called flexibility, both in the form of flexible individual decisions and of socially transmitted (cultural) innovations. Although comparison with other species is difficult, the extent of such flexibility is almost certainly limited by brain size. It is shown that brains can only increase relative to body size where the cognitive benefits they produce are reliably translated into improved survival rate. This means that organisms that are very small, face many predators, live in highly seasonal environments, or lack opportunities for social learning cannot evolve greater flexibility, and must achieve local adaptation through selection on specific genotypes. On the other hand, as body and brain size increase, local adaptation is increasingly achieved through selection on plasticity. The species involved are also generally those that most need it, being more mobile and longer-lived. Although high plasticity buffers against environmental change, the most flexible organisms face a clear limit because they respond slowly to selection. Thus, paradoxically, the largest-brained animals may actually be vulnerable to the more drastic forms of environmental change, such as those induced by human actions.

Development of the social behavior of two mice species with contrasting social systems

The house mouse (Mus musculus) and the mound-building mouse (M. spicilegus) differ in their mating and social systems. The M. musculus is polygynous and females tend to breed cooperatively while M. spicilegus is known to be monogamous and famous for its unique cooperative behavior; the communal overwintering. Mus spicilegus is considered as a highly aggressive species in the genus Mus. In the present study, we attempted to analyze the development of aggressive and sociable behavior in these species and to discover how familiarity with the target moderates the development of sociable and aggressive behaviors and moderates the differences between the species. Dyadic social interaction tests in neutral cages were performed on 21-, 60-, and 120-day-old mice of both genders and both species. Each individual was tested against a sibling and an unfamiliar individual at all three ages. Our results showed that the development of aggressive and sociable behavior with age differed between the species and sexes; however, familiarity with the other mouse moderated the effect of species on aggression. At 21 days, both genders of M. spicilegus were more aggressive against strangers than siblings. This became true of both species at 60 days. When facing a stranger, both sexes of M. spicilegus were more aggressive than M. musculus at 120 days. However, when facing a sibling, neither gender of M. spicilegus was more agonistic than M. musculus, indicating that either kinship or early social experiences elicit tolerance.

Multiple geographic origins of commensalism and complex dispersal history of Black Rats

The Black Rat (Rattus rattus) spread out of Asia to become one of the world's worst agricultural and urban pests, and a reservoir or vector of numerous zoonotic diseases, including the devastating plague. Despite the global scale and inestimable cost of their impacts on both human livelihoods and natural ecosystems, little is known of the global genetic diversity of Black Rats, the timing and directions of their historical dispersals, and the risks associated with contemporary movements. We surveyed mitochondrial DNA of Black Rats collected across their global range as a first step towards obtaining an historical genetic perspective on this socioeconomically important group of rodents. We found a strong phylogeographic pattern with well-differentiated lineages of Black Rats native to South Asia, the Himalayan region, southern Indochina, and northern Indochina to East Asia, and a diversification that probably commenced in the early Middle Pleistocene. We also identified two other currently recognised species of Rattus as potential derivatives of a paraphyletic R. rattus. Three of the four phylogenetic lineage units within R. rattus show clear genetic signatures of major population expansion in prehistoric times, and the distribution of particular haplogroups mirrors archaeologically and historically documented patterns of human dispersal and trade. Commensalism clearly arose multiple times in R. rattus and in widely separated geographic regions, and this may account for apparent regionalism in their associated pathogens. Our findings represent an important step towards deeper understanding the complex and influential relationship that has developed between Black Rats and humans, and invite a thorough re-examination of host-pathogen associations among Black Rats.

No postnatal maternal effect on male aggressiveness in wild-derived strains of house mice

Male aggressiveness is a complex behavior influenced by a number of genetic and non-genetic factors. Traditionally, the contribution of each of these factors has been established from experiments using artificially selected strains for high/low aggressive phenotypes. However, little is known about the factors underlying aggressive behavior in natural populations. In this study, we assess the influence of genetic background vs. postnatal maternal environment using a set of cross-fostering experiments between two wild-derived inbred strains, displaying high (STRA, derived from Mus musculus domesticus) and low (BUSNA, derived from Mus musculus musculus) levels of aggressiveness. The role of maternal environment was tested in males with the same genetic background (i.e. strain origin) reared under three different conditions: unfostered (weaned by mother), infostered (weaned by an unfamiliar dam from the same strain), and cross-fostered (weaned by a dam from a different strain). All males were tested against non-aggressive opponents from the A/J inbred strain. Resource-holding potential was assessed through body weight gains and territory ownership. The STRA males were shown to be aggressive in both neutral cage and resident-intruder tests. On the contrary, the BUSNA males were less aggressive in all tests. We did not find a significant effect of postnatal maternal environment; however, we detected significant maternal effect on body weight with differences between the strains, fostering type and interactions between these factors. We conclude that the aggressiveness preserved in the two strains has significant genetic component whose genetic basis can be dissected by quantitative trait loci analysis.

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.

Characterization and comparison of major urinary proteins from the house mouse, Mus musculus domesticus, and the aboriginal mouse, Mus macedonicus

Urine from the house mouse, Mus musculus domesticus, contains a high concentration of major urinary proteins (MUPs), which convey olfactory information between conspecifics. In wild populations, each individual expresses a different pattern of around 8 to 14 electrophoretically separable MUP isoforms. To examine whether other Mus species express MUPs and exhibit a similar level of individual heterogeneity, we characterized urinary proteins in urine samples from an aboriginal species, Mus macedonicus, captured from different sites in Turkey. Anion exchange chromatography and electrospray ionization mass spectrometry demonstrated that M. macedonicus urine contained a single major peak of mass 18,742 Da, and in contrast to M. m. domesticus, all individuals were the same. The M. macedonicus masses were not predicted from any known MUP gene sequence. Endoproteinase Lys-C (Lys-C) digestion of the purified M. macedonicus urinary protein followed by matrix assisted laser desorption time of flight (MALDI-TOF) mass spectrometry demonstrated that it shared considerable, but not complete, sequence homogeneity with M. m. domesticus MUPs. Three M. macedonicus Lys-C peptides differed in mass from their M. m. domesticus counterparts. These three peptides were further characterized by tandem mass spectrometry. The complete sequences of two were determined, and in conjunction with methyl esterification, the amino acid composition of the third was inferred, and the sequence narrowed down to three permutations. The complete M. macedonicus sequence contained a maximum of seven amino acid substitutions, discernible by tandem mass spectrometry, relative to a reference M. m. domesticus sequence. Six of these were on the surface of the molecule. Molecular modeling of the M. macedonicus sequence demonstrated that the amino acid substitutions had little effect on the tertiary structure. The differences in the level of heterogeneity between the two species are discussed in relation to their environment and behavior. In addition, the differences in protein structure allow speculation into molecular mechanisms of MUP function.

Influence of latent toxoplasmosis on the secondary sex ratio in mice

The sex ratio may be influenced by many factors, such as stress and immunosuppression, age of parents, parity and sex of preceding siblings. In animal systems, parasitism often changes the sex ratio of infected hosts, which can increase the probability of their transmission. The most common human protozoan parasite in developed countries, Toxoplasma gondii (prevalence 20%-80%), is known to change the behaviour of its intermediate hosts, thereby increasing the probability of transmission to its definitive host (the cat) by predation. The intermediate hosts, which under natural conditions are rodents, serve as the vector for Toxoplasma. Therefore, we speculate that Toxoplasma can alter the secondary sex ratio (i.e. male to female ratio in the offspring) of infected females to increase the proportion of (congenitally infected) male offspring, which are the more migratory sex in most rodent species. Here we studied the sex ratio of experimentally infected laboratory mice, expressed here as the proportion of males in the litter. In accordance with our hypothesis and results of previous retrospective cohort studies on human subjects, mice with toxoplasmosis produced a higher sex ratio than controls, in the early phase of latent infection. In the later phase of infection, mice with congenital toxoplasmosis had a lower sex ratio than controls, which is in accord with the Trivers-Willard hypothesis of sex ratio manipulation, suggesting that females in poor physical condition give birth to more female offspring.

Women infected with parasite Toxoplasma have more sons

The boy-to-girl ratio at birth (secondary sex ratio) is around 0.51 in most populations. The sex ratio varies between societies and may be influenced by many factors, such as stress and immunosuppression, age, primiparity, the sex of the preceding siblings and the socioeconomic status of the parents. As parasite infection affects many immunological and physiological parameters of the host, we analyzed the effect of latent toxoplasmosis on sex ratios in humans. Clinical records of 1,803 infants born from 1996 to 2004 contained information regarding the mother's age, concentration of anti-Toxoplasma antibodies, previous deliveries and abortions and the sex of the newborn. The results of our retrospective cohort study suggest that the presence of one of the most common parasites (with a worldwide prevalence from 20 to 80%), Toxoplasma gondii, can influence the secondary sex ratio in humans. Depending on the antibody concentration, the probability of the birth of a boy can increase up to a value of 0.72, C.I.95 = (0.636, 0.805), which means that for every 260 boys born, 100 girls are born to women with the highest concentration of anti-Toxoplasma antibodies. The toxoplasmosis associated with immunosuppression or immunomodulation might be responsible for the enhanced survival of male embryos. In light of the high prevalence of latent toxoplasmosis in most countries, the impact of toxoplasmosis on the human population might be considerable.