Genetical variation in three Pacific House mouse (Mus musculus) populations

Studies of allozymic variation at 36 loci in samples of House mouse ( Mus musculus ) populations collected from the island of Hawaii and two islets in the Enewetak Atoll, Marshall Islands are reported. All three populations carried a great deal of inherited variation: the Hawaiian sample had a mean heterozygosity of 16.6% per locus, which is the highest value so far found for a mouse population. The mean heterozygosities for the two atoll populations were 11.4% and 10.9%.
There were no changes in either heterozygosity or allozyme frequencies with age. In this respect, these populations from the tropical Pacific differed from populations living in cold temperate regions where natural selection has been shown to affect allele frequencies in different ways at different stages of the life cycle.     

Ecological genetics of an island population of the House mouse (Mus musculus)

The House mouse ( Mus musculus L.) population on the small Welsh island of Skokholm was founded in the 1890s when a few animals were inadvertently introduced. It has thrived ever since. The animals breed from late March to early October, during which time the population increases 8–10 fold. Winter survival is related to temperature: the spring population can be as low as 100 individuals after a cold winter; if the winter is warm, so many animals survive that high numbers may occur in the following autumn. There are no resident predators of the mice, and no other small mammals on the island.
The population was sampled on 20 occasions between 1957 and 1972, and genetical changes measured by the incidences of non-metrical skeletal variants (which describe a substantial proportion of the genome) and (from 1968–72) by allele and genotype frequencies of electrophoretically detected genes. Two sorts of changes occurred: an irregular but increasing deviation from the genetical composition of the population at the beginning of the study period, and an annual cycle with frequencies changing in one direction during the breeding season and the opposite direction in the winter. Samples collected in the autumn were more similar to each other than spring caught samples, which conforms with independent evidence about the differing environmental contributors to death in different winters, as compared with general homogeneity of mortality factors during the summers. It is concluded that the genetical composition of the population is largely dependent on natural selection, although the agents and intensity of selection change with both seasons and years.     

Motivational and Heritable Determinants of Dispersal Latency in Wild Male House Mice (Mus musculus musculus)

Divergence of dispersal regimens has been suggested to be the selective basis for the evolutionary differentiation of agonistic phenotypes found in natural populations of house mice. Dispersal propensity may, therefore, be expected to exhibit heritable variation in wild house mice, ultimately related to motivational differences causing observable differences in agonistic behaviour. To test for heritable components in dispersal propensity in wild house mice, father–offspring regressions of dispersal latencies from residential social groups were determined in standardized seminatural social settings. To evaluate potential motivational causes of phenotypic variation in dispersal behaviour, all test animals (fathers, sons, and daughters) were scored prior to the dispersal experiment in a standardized behavioural test, at 60 d of age. Activities were monitored in a 1 m² square test arena during 10‐min observation periods. Test arenas exhibited four equidistant openings leading to cages containing fresh, own, sibling, or foreign bedding material. The apparatus allowed for scoring anxiety, exploratory activity, and kin preference. Subsequently, test animals were exposed to a resident population in a semi‐natural enclosure providing a dispersal opportunity. Father–son regressions of dispersal latencies were significantly positive, but no significant relationship was found for daughters. Dispersal latency decreased with increasing exploratory activity scores in males, but increased in females. Anxiety as well as kin preferences did not affect dispersal propensity. Hence sex‐linked, motivational components reflect heritable social behaviour variation in male house mice that may ultimately be caused by diverging dispersal regimens.     

Spontaneous thyroid follicular adenoma in a laboratory mouse (Mus musculus)

Spontaneous thyroid micro-follicular adenoma was found in an 18-month-old nursing Swiss albino mouse. The lesion was first noted as a tiny bulge at the base of the neck. The tumor was solid, and within two months, had grown such an enormous size that movement, feeding and suckling of the litter were greatly hampered. The litter of seven mice later died due to improper nursing while their mother remained generally unaffected by the mass.     

The skeletal correlates of behavioral modification in the laboratory mouse (Mus musculus)

The effects of behavioral modification on the skeletal morphology of the laboratory mouse (Mus musculus) are investigated. Climibing, with increrased prehensile use of the foot, is found to bring about significant changes in metatarsal and long bone morphology. Differences in metatarsal robusticity related to weight-bearing differences associated with different locomotor patterns are reported for a natural history setting for Peromyscus.     

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%.     

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.     

Some characteristics of the XO mouse (Mus musculus L.) II. Reproduction: fertility and gametic segregation

A preliminary investigation of reproductive capacity in XO mice showed that they produced smaller litters than normal litter mates. More time elapsed between successive litters when kept in the presence of a male except during pregnancy and weaning. This lower level of reproduction is manifest during the whole reproductive period. Also reproductive capacity in XO mice reaches its maximum and minimum (end of reproductive period) earlier than in normals.Further study also demonstrated an underdevelopment of the ovaries-the whole ovary, as well as the numbers of maturing and mature follicles, are smaller in XO mice than in controls. Since these differences can be corrected by unilateral ovariectomy, they appear to be under control of extra-ovarial factors, e.g. of gonadotropic hormone(s). The data also suggest depression of activity in the oestrogen-producing system, and in general that the lower reproductivity of XO mice may be attributed to a diminished secretion of gonadotropic hormones together with a smaller number of primordial germ cells in XO mice.The segregation from XO parents seems to favor transmission of X-gametes in young mothers, with however the preference for X tending to decrease with parental age. Since the data tend to rule out postzygotic selection effects, the excess of X-bearing gametes may relate to meiotic drive.     

Expression of glucose phosphate isomerase in interspecific hybrid (Mus musculus x Mus caroli) mouse embryos.

Hybrid Mus musculus x Mus caroli embryos were produced by inseminating M. musculus (C57BL/OlaWs) females with M. caroli sperm. Control M. caroli embryos developed more rapidly than did control M. musculus embryos and implanted approximately 1 day earlier. At 1 1/2 days, both the hybrid embryos and those of the maternal species (M. musculus) had cleaved to the 2-cell stage. By 2 1/2 days some of the hybrids were retarded compared to M. musculus, and by 3 1/2 days most were lagging behind. This is consistent with the idea that the rate of development of hybrid embryos declines once it becomes dependent on embryo-coded gene products. We have used this difference in rate of preimplantation development, between hybrid and M. musculus embryos, to try to determine whether the activation of embryonic Gpi-1s genes, that encode glucose phosphate isomerase (GPI-1), is age-related or stage-related. In control M. musculus embryos (both mated and Al groups), the GPI-1AB and GPI-1A allozyme, indicative of paternal gene expression, were detected in 7 of 9 samples of 3 1/2-day compacted morula stage embryos and were seen in all 19 samples of 3 1/2-day blastocysts. In hybrid embryos, these allozymes were detected 1 day later. They were not detected in any 3 1/2-day samples (12 samples of compacted morulae) but were consistently detected at 4 1/2 days (4 samples of blastocysts and 2 samples of uncompacted morulae). Our interpretation of the results is that gene activation in hybrid embryos is stage-specific, rather than age-specific, and probably begins around the 8-cell stage, with detectable levels of enzyme accumulating later. Analysis of GPI-1 electrophoresis indicated that both the paternal (M. caroli) and maternal (M. musculus) Gpi-1s alleles were equally expressed in hybrid embryos and that the paternally derived allele was not activated before the maternally derived allele.     

Two types of mouse (Mus musculus domesticus) Y chromosomes in Quebec.

A Y chromosomal repetitive sequence identified two types of Y chromosomes in mice (Mus musculus domesticus) caught near Ste. Anne de Bellevue, Quebec. One type is apparently identical to the Y chromosome found in Maryland, Delaware, and California, whereas the other type is similar, but not identical, to the Y chromosome present in M.m. poschiavinus, an Alpine race of M.m. domesticus. These findings suggest that the domesticus Y chromosome is highly polymorphic and thus useful for elucidating the relationships among American and European house mouse populations.     

The inheritance of patterns of metameric variation in the mouse (Mus musculus) vertebral column

In this paper, we examine the patterns of metameric variation shown by different dimensions of vertebrae from the mouse vertebral column. We examine differences in metameric variation between variables within an inbred strain and compare patterns of metameric variation between inbred strains and between inbred strains and their F₁ S. We make both visual and numerical comparisons, the latter being based upon a novel application of Fourier analysis. Comparisons between dimensions within a strain reveal two distinct patterns of metameric variation within the column. The first, shown only by the antero-posterior (dorso-ventral) diameter of the neural canal, is relatively simple: dimensions become progressively smaller caudally. The second is more complex, with two peaks, and appears more closely related to somatic structures. The second pattern may be modified according to the temporal pattern of development of different vertebral elements. Comparisons between mouse strains suggest that those variables which complete growth early, and which preserve the basic patterns of metameric variation in a relatively unmodified form, are best suited to discriminating between inbred strains. The F_l S between inbred strains show patterns of metameric variation which in some cases are more like those of one parental strain and in others more like those of the other parental strain. We consider the significance of these findings in relation to further studies of mammalian vertebral column genetics, development and evolution.