A review of the endoparasites of wild House Mice Mus domesticus

A tabular checklist of the parasites of wild House Mice Mus domesticus is presented, with data on prevalence rates and geographic location. Parasites most often recorded are: Syphacia obvelata, Taenia taeniformis, Aspiculuris tetraptera, Hymenolepis diminuta and Trichuris maris. The near-global distribution of House Mice and their ability to survive in a wide range of conditions render House Mouse parasites ideal for the study of environmental influences on parasites and transmission of parasites to new hosts.     

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

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

Food neophobia in wild and laboratory mice (Mus musculus domesticus)

In a conditioned taste aversion procedure we were specifically interested in the topic of food neophobia. Wild and laboratory mice were individually presented with a novel drink (0.1 % saccharin solution). Compared with the daily water consumption, the intake of this was lower. This decrease was greater:(1) in wild than in tame populations ; (2) in random-bred (Swiss-albinos) than in inbred (C57 B1/6, BALB/c) strains ; (3) in F₁-hybrids (either wild x tame or inbred x inbred) than in the parental strains.These results are discussed:(1) in terms of a selective pressure linked to man's fight against rodents, leading to increased neophobia in wild mice ; and (2) by stressing the heterosis an inbreeding depression effects, which suggest that food neophobia is a component of Darwinian fitness.     

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

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

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.     

Mating behaviour and female choice: their relation to social structure in wild caught House mice (Mus musculus) housed in a semi-natural environment

Mating behaviour and its relation to social structure was studied in two colonies of wild caught House mice ( Mus musculus ) housed in semi-natural environments. In both colonies, one male was initially dominant to (chased) a number of subordinate males, and mated significantly more often than subordinate males. In time, younger males deposed the dominant male and set up defended areas in the observation room. Under this territorial social structure, only males who possessed defended areas mated. Females moved freely throughout the observation room, and chose high quality territories in which to deliver their litters. Females mated significantly more often with a) males in whose territories they delivered their litters and b) males who defended'high quality'territories.     

Oxytocin inhibits infanticide in female house mice (Mus domesticus)

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

The genomic basis of high-elevation adaptation in wild house mice (Mus musculus domesticus) from South America

Understanding the genetic basis of environmental adaptation in natural populations is a central goal in evolutionary biology. The conditions at high elevation, particularly the low oxygen available in the ambient air, impose a significant and chronic environmental challenge to metabolically active animals with lowland ancestry. To understand the process of adaptation to these novel conditions and to assess the repeatability of evolution over short timescales, we examined the signature of selection from complete exome sequences of house mice (Mus musculus domesticus) sampled across two elevational transects in the Andes of South America. Using phylogenetic analysis, we show that house mice colonized high elevations independently in Ecuador and Bolivia. Overall, we found distinct responses to selection in each transect and largely nonoverlapping sets of candidate genes, consistent with the complex nature of traits that underlie adaptation to low oxygen availability (hypoxia) in other species. Nonetheless, we also identified a small subset of the genome that appears to be under parallel selection at the gene and SNP levels. In particular, three genes (Col22a1, Fgf14, and srGAP1) bore strong signatures of selection in both transects. Finally, we observed several patterns that were common to both transects, including an excess of derived alleles at high elevation, and a number of hypoxia-associated genes exhibiting a threshold effect, with a large allele frequency change only at the highest elevations. This threshold effect suggests that selection pressures may increase disproportionately at high elevations in mammals, consistent with observations of some high-elevation diseases in humans.     

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

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

Validating standardised personality tests under semi‐natural conditions in wild house mice (Mus musculus domesticus)

Personality traits in animals are often measured using standardised behavioural tests for activity, boldness/shyness, sociability, aggression and exploration. These tests are quick and convenient, as well as easy to repeat. As the interest in studying the impact of animal personality on ecological and evolutionary consequences has been growing rapidly, there is increasing focus on cross‐validating measurements taken during these tests with behaviours shown under natural situations. In our experiment, we aimed to study the relationship between standardised measurements for activity, exploration and anxiety‐like behaviour measured in Open Field, Novel Object and Elevated Plus Maze tests with exploration and colonisation in semi‐natural conditions. We carried out a semi‐natural enclosure experiment in parallel with standardised behavioural tests, creating a scenario similar to an invasion or dispersal event. We compared behaviours in standardised tests and in enclosures for animals of two populations of wild house mice (Mus musculus domesticus). Several behavioural variables taken during the standardised tests, such as distance moved and time spent with novel object, were negatively correlated with space‐use in the enclosure while being highly positively correlated among each other. Based on their relationship with space use, we refer to behavioural measurements from standardised tests as activity/exploration. The time spent near the walls in an open field, probably reflecting anxiety, was not correlated to any other variable or the behaviour in the enclosure. In addition, we found differences in activity/exploration behaviour between the two populations in the standardised tests, but not during the colonisation of the novel environment. These results emphasise that researchers have to be careful when trying to extrapolate behaviour shown in standardised laboratory test setups to more natural, ecologically relevant situations. This has to be taken into account in distantly related species but even when studying the wild relative of laboratory rodents, for which these standardised tests have originally been developed.     

Dispersal mechanisms in a captive wild house mouse population (Mus domesticus Rutty)

The ecological implications of dispersal have been discussed in many studies of wild animals in the field but little is known about the social mechanisms leading to the emigration of certain members of a group. To study the social background of dispersal in wild house mice ( Mus domesticus Rutty) a population cage system was evaluated that allowed permanent observation of individually marked animals. It consisted of ten cages connected to a central cage by transparent plastic tubes. Two of these cages were defined as 'dispersal cages' and could be reached only by swimming through a water basin. Dispersal was defined as a permanent stay in one of these cages for at least 4 days. At the beginning of the experiment one pair of house mice with their litter was placed into the cage system. Each of six experiments lasted for 6 months during which data on spacing, social interactions, body condition, reproduction, mortality and dispersal were collected by daily observations. Results regarding this study could be summarized as follows: (1) dispersal in house mice is male-biased; (2) there are interfamiliar differences in dispersal age, dispersal rate, and in the development of the population structure; (3) after reaching sexual maturity subdominant males are evicted by the dominant one; (4) reproductive rate among females drops with increasing birth order, thus only the oldest females within a group reproduce; (5) females born under high population density conditions can only reproduce after dispersal.     

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.     

Kin Recognition and Maternal Care under Restricted Feeding in House Mice (Mus domesticus)

This study tests the hypothesis that female house mice (F1 generation of wild caught Mus domesticus) should preferentially invest in own offspring if confronted with young of different degrees of relatedness. The maternal behaviour of females with litters of 4 own and 4 unrelated alien young (cross-fostered at day 1 of lactation) was analysed during a lactation period of 22 days both under ad libitum and under restricted feeding (food was restricted by 20%). Cross-fostering and restricted feeding had no effect on the amount of time spent nursing until weaning. Under both feeding conditions the females did not differ in their maternal behaviour towards own and alien young: there were no significant differences either in the amount of time spent nursing own versus alien pups or in the time spent licking own versus alien young. Weight gain of own and alien = wild littermates did not differ significantly in mixed litters and was similar both under ad libitum and under restricted feeding. Such indiscriminate behaviour might be adaptive if female house mice prefer to communally nest with a relative and thus improve their inclusive fitness by investing in own and related offspring in a communal nest. Under moderate restricted feeding females could not wean the entire litter but reduced litter size by cannibalizing on average 2.7 pups (75% of the pups were killed when they were 4–8 days old). Females with cross-fostered litters killed as many own as alien young. This suggests that females cannot discriminate between own and unrelated young if cross-fostering takes place at day 1 of lactation. Besides testing kin recognition abilities, the experiments also allow analysis of the weaning strategy of females under food shortage. Under restricted feeding, body weight of the females was significantly lower during middle lactation than under ad libitum feeding. Weaning weight of young in reduced litters under food restriction (9–10 g) did not differ significantly from weaning weight of young in litters of 7–10 young, but was lower than that of young in similar sized litters (litter size 6), under ad libitum feeding. The maternal behaviour of cannibalizing some young under food shortage can be interpreted as a weaning strategy which results in the largest number of offspring that can be raised to a minimal weaning weight of 9–10 g. Such a weaning strategy might represent a favourable trade-off between number and size of young produced.     

Urine marking and social dominance in male house mice (Mus musculus domesticus)

House mice use urine marking for a variety of forms of social communication. Urine marking varies with dominance status; socially dominant male house mice urine mark more than those that are socially subordinate. Experiment I was designed to confirm this previous finding. Experiment II was designed to test whether urine marking, measured prior to testing males for aggression, could be used to predict social dominance. Mice were tested for urine marking in 20 cmx40 cm rectangular cages with filter paper below the wire mesh bottom of the cage. In Experiment I, groups of four males were tested in a round robin design to assess social dominance and were then placed individually in urine marking cages. Social dominance was a significant predictor of the number of 1 cm squares that contained urine marks, both with regard to interior squares and for perimeter squares in the test cage. In Experiment II, groups of four males were first tested individually in urine marking cages and then used for round robin aggressive encounters to assess social dominance. The number of interior squares with urine marks, and, to a lesser extent, the number of perimeter squares with urine marks, were both significant predictors of aggression scores and social dominance status. Being able to judge social dominance without having the mice encounter each other could be a valuable tool for future work; confounding effects on such parameters as hormone levels could be avoided while obtaining an estimate of male social dominance status.     

Seasonal variation in fertility, fecundity and litter sex ratio in laboratory and wild stocks of house mice (Mus domesticus)

Data compilations were made for three parameters pertaining to reproduction in a domestic strain (14 years) and a wild stock (4 years) of commensal house mice: (a) the percentage of females mated that produced litters; (b) the average number of pups per litter; and (c) the sex ratio of the pups in the litters. Fecundity and fertility varied seasonally in both domestic and wild mice. More females become pregnant and litter sizes were larger in the spring, summer, and fall months than during the winter season. Sex ratios also varied seasonally with more male biased litters produced during the 4 winter months. There appear to be seasonal shifts in productivity for both stocks of mice and these seasonal trends have not been altered by domestication under laboratory conditions. In spite of the fact that house mice are generally opportunistic, it is possible that there has been selection in the mice for shifting rates of production in relation to the best seasons of the year in terms of climate and resource availability. The higher production of males during summer months may be geared toward greater success in dispersal at that season and a higher probability that the males can find a territory and mate successfully in summer rather than winter. These results have potential implications for animal breeders and for those who maintain mouse colonies to produce animals for scientific investigations.     

Changes among wild House mice (Mus musculus) bred for ten generations in a cold environment, and their evolutionary implications

Wild House mice, Mus musculus , bred at 23°C (controls) changed little in reproductive performance over ten generations. Similar mice bred at 3°C (Eskimo) became more fertile and heavier. Eskimo body fat also rose. Control adrenal weights declined; Eskimo adrenal weights were heavier than those of controls, but only during the first four generations. The Eskimo phenotype after ten generations was a combined result of a direct response to cold, parental effects and genetical changes in the Eskimo population. Maternal effects were probably especially important. In such conditions, the minimum unit of selection that it is useful to consider is the female and her litter.