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.     

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.     

Patterns of infection by Salmonella and Yersinia spp. in commensal house mouse (Mus musculus domesticus) populations

AIMS: This study sought to examine the risk posed by house mice transmitting pathogens to livestock on typical mixed-agriculture farms in the UK. METHODS AND RESULTS: In a 10-month longitudinal study at one farm, 222 faecal samples were taken from mice and 57 swabs from the farm environment; 3.2% and 15.8%, respectively, were positive for Yersinia. Seventy-five intestinal samples were taken from house mice from three other farms and 9.3% were positive for Yersinia. The commonest species was Y. enterocolitica (of a wide range of serotypes); all isolates were non-pathogenic, except one of Y. pseudotuberculosis. Salmonella was not isolated from any sample. CONCLUSION: This study provides additional evidence that house mice are generally not significant vectors of either pathogenic Yersinia strains or Salmonella species. SIGNIFICANCE AND IMPACT OF THE STUDY: This is the first longitudinal study of Yersinia in any small mammal population, and shows infection to be a dynamic series of generally non-pathogenic, transient infections.     

Intracranial androgenic and estrogenic stimulation of male-typical behaviors in house mice (Mus domesticus).

Two experiments in house mice (Mus domesticus) examined the neural sites at which steroid hormones activate the following male-typical behaviors: 70 kHz ultrasonic mating vocalizations in response to stimulus females or their urine, urinary marking in response to stimulus males or stimulus females, mounting of estrous females, and intermale aggression. In the first experiment, four groups of castrated males received bilateral intracranial implants of testosterone (T) into either the septum (SEPTUM), medial preoptic area (MPO), anterior hypothalamus (AHA), or ventromedial hypothalamus (VMH). Two control groups received subcutaneous silastic capsules of T (TSIL) or empty silastic capsules (BSIL). The TSIL males performed all behaviors at male-typical levels while the BSIL males were unresponsive. MPO males emitted ultrasonic mating vocalizations at high levels while few vocalizations were seen in males of the other brain implant groups. The VMH, AHA, and MPO males urine marked at higher levels than the BSIL males but did not exhibit the high levels of the TSIL males. Mounting was observed only in MPO and TSIL males. Aggression was rare in males from any of the brain implant groups. In the second experiment, the hormone activity of the implants was increased by using testosterone propionate (TP) or a 50% mixture of estradiol (E2) and cholesterol. The six groups were SEPTUMTP, SEPTUME2, MPOTP, MPOE2, TPSIL, and BSIL. The TPSIL males performed all behaviors at male-typical levels while the BSIL males were unresponsive. TP was effective at restoring vocalizations and urine marking only when placed in the MPO; however, E2 was effective at both sites. Again aggression and mounting were less evident in the brain implanted males. In conclusion, implants of T or TP were effective in restoring ultrasonic mating vocalization when placed into the MPO. MPO implants of T and TP were also effective in stimulating urine marking, although VMH and AHA implants also showed some effectiveness. The restorative effects of E2 were not localized which is probably related to the greater hormonal activity of this treatment. Comparisons of the properties of the various brain implants to restore more than one behavior were discussed.     

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.     

The population ecology of house mice (Mus domesticus) on the Isle of May, Scotland

The colonizing ability, catholic habitat utilization and wide distribution of house mice ( Mus domesticus , Rutty) are indicators of their ecological resilience. Numerous studies have been made of commensal, caged and free-living mouse populations though few have assessed the relative importance of physiological and genetical components of adaptability in a simple ecosystem. This paper reports such findings, derived from live-trapping which formed part of an inter-disciplinary study of adaptability in a feral population of house mice living on a small Scottish island (57 ha).
The population size ranged from450–3250 animals. A high proportion of mice showed homerange tenacity, though15–20% shifted their range during winter. This 'churning' of the population is consistent with the island population forming an effectively panmictic unit rather than fragmented demes. The breeding season, survival of individuals and change in population size related to patterns of gross climatic variation (temperature and rainfall) so that rates of reproduction and survival were lowest in cold, wet conditions. Thermoregulatory adjustment of the mice to lowered ambient temperatures and its contribution to overwinter survival are discussed. Genetical monomorphism of May Island mice is discussed in relation to their biological performance compared with other populations, especially that of the ecologically comparable Skokholm Island (Wales).     

Norwegian house mice (Mus musculus musculus/domesticus): distributions, routes of colonization and patterns of hybridization

We investigated the distributions and routes of colonization of two commensal subspecies of house mouse in Norway: Mus musculus domesticus and M. m. musculus. Five nuclear markers (Abpa, D11 cenB2, Btk, SMCY and Zfy2) and a morphological feature (tail length) were used to differentiate the two subspecies and assess their distributions, and mitochondrial (mt) D‐loop sequences helped to elucidate their colonization history. M. m. domesticus is the more widespread of the two subspecies, occupying the western and southern coast of Norway, while M. m. musculus is found along Norway’s southeastern coast and east from there to Sweden. Two sections of the hybrid zone between the two subspecies were localized in Norway. However, hybrid forms also occur well away from that hybrid zone, the most prevalent of which are mice with a M. m. musculus‐type Y chromosome and an otherwise M. m. domesticus genome. MtDNA D‐loop sequences of the mice revealed a complex phylogeography within M. m. domesticus, reflecting passive human transport to Norway, probably during the Viking period. M. m. musculus may have colonized earlier. If so, that leaves open the possibility that M. m. domesticus replaced M. m. musculus from much of Norway, with the widely distributed hybrids a relict of this process. Overall, the effects of hybridization are evident in house mice throughout Norway.     

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.     

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.     

Genetic variation and correlations between genotype and locomotor physiology in outbred laboratory house mice (Mus domesticus).

Laboratory strains of house mice (Mus domesticus) are increasingly used as model organisms in evolutionary physiology, so information on levels of genetic variation is important. For example, are levels of genetic variation comparable to those found in populations of wild house mice? We studied allozymes to estimate genetic variation in outbred Hsd:ICR mice, which have been used in several studies with evolutionary emphasis. The physiological significance of allozyme variation remains obscure. Several workers have reported relationships between multi-locus heterozygosity and metabolic traits, but endotherms have not been studied. Therefore, we also measured mice for basal metabolic rate (BMR), maximal oxygen consumption during forced treadmill exercise (VO2max), and 12 other traits related to locomotor physiology, before genotyping them for 10 allozyme loci. Four of these loci were polymorphic, all were in Hardy-Weinberg equilibrium, and inbreeding coefficients were not significantly different from zero. Average heterozygosities were 11%, similar to values reported for wild populations of house mice. Fourteen percent of the associations between single-locus genotype and physiological traits were statistically significant. Multi-locus heterozygosity was not significantly related to VO2max, but was positively correlated with BMR, a result opposite to the negative correlation between standard metabolic rate and heterozygosity reported in many ectotherms. Therefore, the proposed mechanisms for the effect of multi-locus heterozygosity on metabolic rate in ectotherms may not apply to endotherms.     

Water flux and energy use in wild house mice (Mus domesticus) and the impact of seasonal aridity on breeding and population levels

Summary Water turnover rate (WTR), urine concentration and field metabolic rate (FMR) were examined in house mice, Mus domesticus, permanently inhabiting roadside verge areas and seasonally invading crops in semi-arid wheatlands in South Australia. FMR was approximately proportional to body mass^0.5 and mean values varied from 4.8 ml CO₂ g^–1h^–1 (2.9 kJ g^–1d^–1) in autumn and winter, to 7.0 ml CO₂ g^–1h^–1 (4.2 kJ g^–1d^–1) in maturing crops during spring. WTR was independent of body mass, indicating that larger mice were selecting a diet containing moister foods. WTR was low in summer and high in winter, and in mice from crops varied from 165 ml l^–1 body water d^–1 (122 ml kg^–1d^–1) to 1000 ml l^–1d^–1 (725 ml kg^–1d^–1). Seasonal changes in WTR were less extreme on the roadside, where a greater diversity of food was available. In the crops, breeding occurred throughout summer during two of three years, but the population increased only in the one summer when mice had marginally higher WTR. On the roadside breeding and population growth were continuous during summer, except in a drought year. Avcrage urine concentration was inversely related to WTR, and varied from 2.0 to 4.8 Osm l^–1. The data indicate that the water conserving abilities of mice equal those of many desert rodents. The water conserving abilities of mice living in crops during summer were fully extended, and in some years aridity limited breeding success and population levels. The degree of moisture stress to which mice are exposed during summer appears to depend not only on rainfall but also on other factors such as availability of food and shelter, and the level of weed infestation in crops.     

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.     

The structure of a chromosomal hybrid zone of house mice (Mus domesticus) in central Italy: cytogenetic analysis

Parapatric hybridization between the chromosomal race “CD” (2n = 22) and standard karyotype populations (2n = 40) of Mus domesticus occurs extensively in central Italy. The present paper reports the results of a ctogenetic surve on a transect crossin the hybrid zone north of Rome. No clinal variation in eitier diloid nuders and chromosome frequencies was found to occur in this area, and drift seems to be responsible for the observed atchy pattern of variation. The previous assumption of a strong fertility reduction in structuray heterozyous hybrids contrasts sharply with the width (32 km) of the zone and the average structural aeterozygosity of the hybrid poulations. It is suggested that fitness of structural heterozygotes in nature is not strongly aPfected as has been inferred from laboratory experiments. The results of this study are discussed in context together with the role of hybrid zones in chromosomal speciation in Mus domesticus.     

The frequency of multiple paternity suggests that sperm competition is common in house mice (Mus domesticus)

Sexual selection is an important force driving the evolution of morphological and genetic traits. To determine the importance of male-male, postcopulatory sexual selection in natural populations of house mice, we estimated the frequency of multiple paternity, defined as the frequency with which a pregnant female carried a litter fertilized by more than one male. By genotyping eight microsatellite markers from 1095 mice, we found evidence of multiple paternity from 33 of 143. Evidence for multiple paternity was especially strong for 29 of these litters. Multiple paternity was significantly more common in higher-density vs. lower-density populations. Any estimate of multiple paternity will be an underestimate of the frequency of multiple mating, defined as the frequency with which a female mates with more than a single male during a single oestrus cycle. We used computer simulations to estimate the frequency of multiple mating, incorporating observed reductions in heterozygosity and levels of allele sharing among mother and father. These simulations indicated that multiple mating is common, occurring in at least 20% of all oestrus cycles. The exact estimate depends on the competitive skew among males, a parameter for which we currently have no data from natural populations. This study suggests that sperm competition is an important aspect of postcopulatory sexual selection in house mice.     

Adaptive energetics in house mice, Mus musculus domesticus, from the island of Porto Santo (Madeira archipelago, North Atlantic)

The bioenergetic strategies of house mice (Mus musculus domesticus) from the island of Porto Santo were investigated and compared with those of mice from mainland Portugal. Energy obtained from food ingestion was 18.2% lower in Porto Santo mice than in mainland mice (1.53 vs. 1.87 kJ/g/day). The same pattern was observed for metabolisable energy intake, which was 19.2% lower in island specimens (0.87 vs. 1.08 kJ/g/day for mainland specimens). Apparent digestibility was similar in both groups of mice. Basal metabolic rate (BMR) of Porto Santo individuals was low (1.16 ml O(2)/g/h), representing only 56% of the predicted value, based on body mass, while mainland individuals exhibited a BMR closer to the expected value, corresponding to 87% of the predicted value (1.80 ml O(2)/g/h). Thermoregulatory abilities within the range of 10-28 degrees C ambient temperature did not differ between island and mainland mice. Results suggest an adaptation of Porto Santo mice to the environmental aridity of the island of Porto Santo, leading to a conservative energetic strategy.     

Ejaculate allocation under varying sperm competition risk in the house mouse, Mus musculus domesticus

A common mechanism through which males can enhance their successin postcopulatory contests over paternity is to inseminate moresperm than their rivals. However, ejaculate production is costlyand the evolution of prudent sperm allocation strategies sensitiveto variation in local levels of sperm competition has now beendemonstrated in diverse taxa, including mammals. Theory predictsan increased sperm allocation in response to an elevated riskof sperm competition, but here we show that male house mice(Mus musculus domesticus) instead ejaculate fewer sperm perejaculate when mating in the presence of a rival male. Thissurprising sperm allocation pattern may be a necessary consequenceof adaptive changes in copulatory behavior, enabling males toachieve more rapid sperm transfer and/or to ejaculate repeatedlyunder risk of sexual competition. The size of a second ejaculatecomponent, the copulatory plug, is unaffected by sperm competitionrisk. Our results highlight how the often complex interplaybetween different reproductive traits can affect the evolutionof sperm competition phenotypes.     

Antioxidant gene expression in active and sedentary house mice (Mus domesticus) selected for high voluntary wheel-running behavior

We present liver mRNA levels of the two antioxidant enzymes catalase (CAT) and Mn-superoxide dismutase (SOD2) in four treatment groups of house mice assayed by RNase protection at 20 months of age. These groups were mice from four replicate selection and four replicate control lines from the sixteenth generation of selective breeding for high voluntary wheel running, housed with or without running wheels from age 3 weeks through 20 months. Exercising control females had induced CAT expression; SOD2 exhibited a similar pattern in females from two of the four control lines. Exercising male mice had induced CAT expression, but not SOD2 expression, irrespective of genetic background. We discuss these results with respect to both evolutionary (genetic) and training (exercise-induced) adaptations and explore predictions of these results in relation to the oxidative-damage theory of senescence.     

Maternal-care behavior and life-history traits in house mice (Mus domesticus) artificially selected for high voluntary wheel-running activity

To test the hypothesis that selective breeding for high voluntary wheel running negatively affects maternal performance in house mice, we observed maternal behavior and compared litter size and mass, in replicate lines of selected (N=4) and control (N=4) mice from generations 20 and 21 of an artificial selection experiment. At generation 21, selected-line females ran 2.8-times more revolutions per day than females from random-bred control lines, when tested at approximately 6 weeks of age as part of the normal selection protocol. After giving birth, dams from selected and control lines exhibited similar frequencies of maternal behaviors and also spent similar amounts of time in general locomotor activity at litter ages of both 9 and 16 days. Dams from selected lines also performed equally well as controls in repeated pup-retrieval trials. At first parturition, selected-line dams averaged 2.4 g smaller in body mass as compared with dams from the control lines; however, neither litter size nor litter mass at birth (generation 20) or at weaning (generation 21) differed significantly between selected and control lines. We conclude that, at least under the husbandry conditions employed, maternal behavior and reproductive output at first parturition are genetically independent of wheel-running behavior.