Oxytocin and Social Preference in Female House Mice (Mus musculus domesticus)

In social species, same‐sex individuals may form social bonds behaviourally expressed as individual preferences, resulting in fitness benefits such as increased offspring survival, longevity and group cohesion. As a result of individual preferences, female house mice (Mus musculus domesticus) form social affiliations while communally nursing and may do so with kin or non‐kin. However, the mechanisms behind the formation of such preferences are unknown. Oxytocin has been linked to a range of social behaviours including bond facilitation, social memory and parental care. Here, we experimentally increased oxytocin in pairs of unfamiliar, unrelated females and predicted that females with elevated oxytocin would demonstrate increased affiliative behaviours compared against a control. Subsequently, we tested for the formation of a social preference, using a preference test with the previous partner and a new unfamiliar female. Our results indicated no significant effect of treatment on positive and negative behaviours between females during the three initial cohabitation days. In both treatments, females demonstrated increased socio‐positive behaviours and cohabitation time with their partner and decreased socio‐negative behaviours and latency to meet, over the 3‐d period. During the partner preference test, control but not oxytocin females demonstrated a significant preference for their cohabitation partner, and oxytocin females spent similar amounts of time with both stimulus females. Therefore, increasing peripheral oxytocin appears not to be involved in the facilitation of initial encounters with a stranger but may hinder the formation of a preference for this new partner.     

Genome Patterns of Selection and Introgression of Haplotypes in Natural Populations of the House Mouse (Mus musculus)

General parameters of selection, such as the frequency and strength of positive selection in natural populations or the role of introgression, are still insufficiently understood. The house mouse (Mus musculus) is a particularly well-suited model system to approach such questions, since it has a defined history of splits into subspecies and populations and since extensive genome information is available. We have used high-density single-nucleotide polymorphism (SNP) typing arrays to assess genomic patterns of positive selection and introgression of alleles in two natural populations of each of the subspecies M. m. domesticus and M. m. musculus. Applying different statistical procedures, we find a large number of regions subject to apparent selective sweeps, indicating frequent positive selection on rare alleles or novel mutations. Genes in the regions include well-studied imprinted loci (e.g. Plagl1/Zac1), homologues of human genes involved in adaptations (e.g. alpha-amylase genes) or in genetic diseases (e.g. Huntingtin and Parkin). Haplotype matching between the two subspecies reveals a large number of haplotypes that show patterns of introgression from specific populations of the respective other subspecies, with at least 10% of the genome being affected by partial or full introgression. Using neutral simulations for comparison, we find that the size and the fraction of introgressed haplotypes are not compatible with a pure migration or incomplete lineage sorting model. Hence, it appears that introgressed haplotypes can rise in frequency due to positive selection and thus can contribute to the adaptive genomic landscape of natural populations. Our data support the notion that natural genomes are subject to complex adaptive processes, including the introgression of haplotypes from other differentiated populations or species at a larger scale than previously assumed for animals. This implies that some of the admixture found in inbred strains of mice may also have a natural origin.     

Allozymic Polymorphism Among 14 Populations of the House Mouse, Mus musculus domesticus, From Greece

Nineteen loci from 239 individuals of the house mouse Mus musculus domesticus (Rodentia, Muridae) were analyzed by means of thin layer electrophoresis. The mice were collected from 14 localities of Greece mainly confined to the area of NW Peloponnese, where a Robertsonian (Rb) system is observed. The individuals were chromosomally characterized by nine diploid numbers, the 2n = 24, 26, 27, 28, 29, 30, 31, 32, and 40. The statistic elaboration revealed that all 14 populations studied were not characterized by cohesive demic structure and high inbreed levels while the gene flow among them has resulted in low levels of genetic differentiation. The resulting values for Neis genetic distance corresponded to distances known for the level of geographical populations of, M. musculus. Wagners cladogram for the phylogenetic relations between the populations studied implied that it is the diploid number, rather than the geographical factor, that characterizes or dominates each population, which mainly influences the phylogenetic relationships.     

Town Mouse, Country Mouse: adaptation and adaptability in Mus domesticus (M. musculus domesticus)

The generally accepted idea that the house mouse is a single, world-wide species which owes its success largely to commensalism with man is wrong. There are at least five European and two Asian species lumped together under the name Mus musculus, plus another fourteen Asian species in the same genus. The house mouse of western Europe is the one that has been introduced to the Americas and Australasia, as well as being domesticated in the laboratory and ‘fancy’ strains; it is properly described as Mus domesticus. A complication of this particular species is the existence of chromosomal races involving the fusion of pairs of chromosomes, apparently at random. These races seem to be reproductively isolated from normal (2n = 40) mice. They have been described in southern Europe and northern Britain. Genetical studies of wild-living mice have shown the operation of powerful natural selection, contrary to earlier assumptions that most of the polymorphic variation in the species (especially that revealed by electrophoresis) was neutral. The effects of such selection are reduced (but not eliminated) by the deme structure of established mouse populations; this social structure is much less rigid than some laboratory experiments have suggested, because of opportunism by individual mice in replacing dead or debilitated animals, and filling new niches as these become available. Virtually every mouse population is unique, since a population tends to be founded by a small group of animals drawn from a genetically variable ancestral population. This differentiation has allowed laboratory workers to develop inbred strains with characteristic properties; it has also resulted in over 130 sub-species being described from wild caught animals. A substantial proportion of these latter have probably arisen by instant sub-speciation through the founder effect. This is well illustrated by the mice of the Faroe islands, which are often quoted as standard examples of extremely rapid evolution. The adaptive properties of the house mouse that have made it such an effective pest and such a good laboratory animal have enabled it to colonize habitats as different as Antarctic tundra and tropical atolls. The species is an ideal one for the general biological task of dissecting the traits that contribute to this adaptability; the material is largely available for this task in the diversity of local forms established in different habitats and characterized genetical varieties maintained in the laboratory. More is known about M. domesticus than any other mammal, except possibly man; the time is ripe for fusing laboratory work on reproduction, mortality, and behaviour with the information increasingly coming from field studies of wild-living animals.     

Impact of Social Ties on Dispersal,Reproduction and Dominance in Feral House Mice (Mus musculus domesticus)

The existence of a relationship between the social ties an individual has to other family members and its further role within the family was tested in feral house mice (Mus musculus domesticus), according to the ‘Social cohesions hypothesis’. It is predicted by the hypothesis that individuals not forming strong social ties are the first who emigrate. House mice were studied using a population cage system that allowed continuous observation of individually marked animals. Data on time staying with other animals (social ties), aggressive interactions, body weight, reproduction, and emigration were collected daily. The results may be summarized as follows:

• 1 Male emigrants were less integrated in cohorts of male littermates compared with their brothers of the same age. These male cohorts appeared to protect single males from attacks by the dominant male. No difference could be observed in social ties to other family members.
• 2 After weaning, there was no difference in social ties of male and female offspring. However, after sexual maturation social ties of males decreased significantly while those of females remained almost constant.
• 3 Female emigrants showed the same intensity of social ties as their resident sisters.
• 4 No difference could be found between social ties of females becoming pregnant and their nonreproductive sisters of the same age. Reproduction or reproductive suppression could not be explained by having more or less contact with other reproductive females.
• 5 Dominant males spent least of all time with other family members.

The social cohesions hypothesis has to be rejected in analysing proximate causes of emigration. In house mice, male emigration was caused by aggression of the dominant male in competition for the top rank within the group. This was enhanced by a lower integration in the group of same-aged brothers but is not related to a lack of integration into the family.     

Evidence for Resetting the Directional Component of Path Integration in the House Mouse (Mus musculus)

Path integration is the animal's running computation of its position relative to a starting point based on recording all displacements. This process is known to be prone to cumulative errors and hence must somehow be corrected with the help of local spatial cues. In the reported experiments, the relative role of local spatial cues at two target locations was appraised. These two targets were the peripheral box of a female house mouse (Mus musculus) and a central box from where she retrieved her pups over a distance of 50 cm. The experimental conditions required the mouse to navigate between the two targets solely by means of path integration. To find out whether the mice continued integrating at the two target locations, directional misinformation was fed into their path integrating system. Hence, passive rotation of 90° proved to be sufficient to decide unambiguously whether the mice were misdirected. Such experimental interference consistently documented ongoing path integration at the target location outside the residential nest. In contrast, the same interference when the mouse was in the residential nest documented discontinuation of path integration in most cases. It is inferred that mice, when departing from residential nests, initially direct themselves by means of local guiding stimuli.     

Genetic and Experiential Features in a Case of Cultural Transmission in the House Mouse (Mus musculus)

The present study analyses the capacity of house mice (Mus musculus) to solve a problem, consisting in opening a door which must be rotated 50 times in the same direction to allow access to the food reward. This capacity emerged spontaneously in 4.8 % of 500 animals belonging to a random bred Swiss population, tested beforehand. The experiment then investigated the effects of genetic and experiential (social) factors on transmission of this capacity from one individual to another. Five groups of approximately 70 animals each were compared: a) controls; b) animals with no experience of the problem but offspring of parents able to solve the problem spontaneously; c) animals with experience of the problem being offspring of parents able to solve it spontaneously; d) naive offspring of parents incapable of solving the problem spontaneously; e) animals with experience of the problem and offspring of parents incapable of solving it. The results showed considerable effects both of genetic and experiential (social) factors with values ranging from only 3.9 % of successful naive mice among offspring of unsuccessful individuals, up to 32.3 % of successful offspring of successful parents, reared with a mother who solved the problem several times in their presence.     

Natural selection in House mice (Mus musculus) from South Georgia (South Atlantic Ocean)

Mice living in tussock grass on a remote headland of the South Atlantic island of South Georgia (54°S) where the mean temperature is less than 2°C and the monthly average below 0°C for four months each year have been studied. They are big animals (although not as large as those on some North Atlantic islands) and have much brown fat, showing their response to their cold environment. Only two out of 27 gene loci scored electrophoretically were segregating (3·4% heterozygosity); these ( Es-6, Got-2 ) are four cross-over units apart on chromosome 8, and were in strong linkage disequilibrium. There were marked changes in allele frequencies with age which go in opposite directions in males and females, showing the action of stabilizing selection: Es-6 ^a increased from 16% in males of less than three months, to 35% in older animals; it declined in females from 36 to 19%.     

Genetic analysis of the hybridization zone between two subspecies Mus musculus domesticus and Mus musculus musculus in Bulgaria

The hybrid zone between the two subspecies of mice Mus musculus domesticus and Mus musculus musculus, which has been studied extensively in Denmark, crosses Europe to the Black Sea through the Alps and the Balkans. Two hundred and seventy-nine animals were captured in 22 localities along a transect across the Balkans. The animals were characterized for seven diagnostic nuclear loci by protein electrophoresis and by restriction pattern analysis of their mitochondrial DNA. The nuclear data show a sharp transition between the two subspecies, most of the variations in allele frequencies (from 0.9 to 0.1) occurring within a 36-km section of the transect. The introgression varies from one locus to the other and is more pronounced, in terms of distance, in M. m. musculus territory. Mitochondrial DNA introgression is important but occurs in one direction only, i.e. from M. m. musculus to M. m. domesticus, while a cytoplasmic transfer from M. m. domesticus to M. m. musculus has been reported. A previous study showed that no Y chromosome introgression occurs. The different behaviour of these three types of markers could be due to the interaction between selection against hybrid genomes and meiotic recombination. Objectively, it would appear that the genes that can introgress are neutral or nearly so and have been separated from deleterious genes they were linked to by recombination. This could explain the differential introgression between autosomal loci. The mitochondrial and Y chromosomes undergo no or very little recombination and each is transmitted as a whole. Their degree of introgression is thus indicative of the intensity of selection resulting from the amount of functional differentiation between the two taxa, which seems to be strong for the Y chromosome and weak for mitochondrial DNA. We propose that the asymmetry of nuclear introgression is due to different population structures. As M. m. musculus is relatively less structured, the rapid spreading of introgressed genes would be favoured. Such a scheme, however, can hardly account for the unidirectionality of the mitochondrial flow, which could be due to sex-dependent behaviour.     

The Effect of Weaning Weight on Offspring Fitness in Wild House Mice (Mus musculus domesticus): A Preliminary Study

Sex allocation theory is frequently applied to mammalian reproductive traits although the basic assumptions are rarely assessed. In particular, it has been proposed that the finding of negative correlations between sex ratio (percentage males) and litter size in a variety of mammals could ultimately be seen as an adaptation according to the Trivers-Willard hypothesis. Thereby it is supposed 1) that individual young of small litters are weaned at heavier weight than young of larger litters, 2) that this litter-size effect on individual weights persists into adulthood, and 3) that such small weight advantages increase male fitness more strongly than female fitness. In this study, during each of 4 trials, I introduced 4 male and 4 female mice from 8 different litters of wild-caught breeding pairs to a semi-natural enclosure and followed up the social and reproductive events for about 10 weeks. It appeared that small weight differences attributable to litter size variation had a significant positive effect on male fitness, but not on female fitness. As the sample size was small and the social development did vary considerably between trials, this result deserves further clarification.     

Reproduction of the House mouse (Mus musculus) in farm buildings

Live and kill traps were used to remove House mice living in granaries, mixed-food stores, dairy units and ancillary stores on farms. Structural weaknesses were common to all buildings. Cavities in walls, in particular, provided favourable living and nesting quarters for mice and were rapidly exploited. The body-weight structure and reproductive traits of the populations in the different habitats were compared. The onset of maturity, in both sexes, was closely related to body-weight increase in the 10 to 14 g range. Breeding, unlike that in most out-door populations in temperate climates, continued throughout the year. Ancillary buildings holding limited food supported small reservoir populations. Mice inhabiting dairy units containing pelleted cattle feed tended to be heavier than those sampled elsewhere and females in the units produced the largest litters. Reproductive performance on farms was intermediate between that of mice occupying urban buildings and corn ricks. There was evidence that environmental and behavioural factors were operating to limit increase in numbers in the dairy units.     

Cryptosporidium tyzzeri and Cryptosporidium muris originated from wild West-European house mice (Mus musculus domesticus) and East-European house mice (Mus musculus musculus) are non-infectious for pigs

Three and 8 week old pigs were inoculated with Cryptosporidium muris HZ206 (Mus musculus musculus isolate), Cryptosporidium tyzerri CR2090 (M. m. musculus isolate) or C. tyzzeri CR4293 (isolate from a hybrid between Mus musculus domesticus and M. m. musculus) at a dose of 1 × 10(7) oocysts per animal. Inoculated pigs showed no detectable infection and no clinical symptoms of cryptosporidiosis during 30 days post infection (DPI), and no macroscopic changes were detected in the digestive tract following necropsy. Developmental stages were not detected in gastrointestinal tract tissue by histology or PCR throughout the duration of the experiment. The infectivity of isolates was verified on SCID mice, in which oocysts shedding started from 4 to 8 DPI. Based on our findings, it can be concluded that pigs are not susceptible to C. muris or C. tyzzeri infection.     

Mitochondrial DNA in the hybrid zone between Mus musculus musculus and Mus musculus domesticus: a comparison of two transects

We studied mtDNA introgression across the contact zone between Mus musculus musculus and M. m. domesticus in two independent transects in the Czech Republic and Bavaria, Germany. A total of 1270 mice from 98 localities in the Czech transect and 456 mice from 41 localities in the Bavarian transect were examined for presence or absence of a Bam HI restriction site in the mt-Nd1 gene. Using this simple mtDNA marker, variants that belonged to the M. m. domesticus lineage (presence of restriction site) could be unequivocally distinguished from those belonging to the M. m. musculus lineage (absence of restriction site). The extent of introgression of mtDNA, three autosomal allozymes and the X chromosome was compared. The introgression of X markers was more limited than was that of the allozymes and mtDNA. In the Czech transect, the centre for the mtDNA cline was shifted about 3.6 km to the west relative to the X chromosome cline, with asymmetric introgression from M. m. musculus to M. m. domesticus . Interestingly, in the Bavarian transect, the centre of the mtDNA cline was shifted about 10.9 km to the east relative to the X chromosome cline, with asymmetric introgression from M. m. domesticus to M. m. musculus, opposite in direction to that observed in the Czech transect.  © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 84 , 363–378.