Cytogenetic studies on wild house mice from Belgium

Staggered chromosomal hybrid zones in the house mouse: relevance to reticulate evolution and speciation

In the house mouse there are numerous chromosomal races distinguished by different combinations of metacentric chromosomes. These may come into contact with each other and with the ancestral all-acrocentric race, and form hybrid zones. The chromosomal clines that make up these hybrid zones may be coincident or separated from each other (staggered). Such staggered hybrid zones are interesting because they may include populations of individuals homozygous for a mix of features of the hybridising races. We review the characteristics of four staggered hybrid zones in the house mouse and discuss whether they are examples of primary or secondary contact and whether they represent reticulate evolution or not. However, the most important aspect of staggered hybrid zones is that the homozygous populations within the zones have the potential to expand their distributions and become new races (a process termed 'zonal raciation'). In this way they can add to the total 'stock' of chromosomal races in the species concerned. Speciation is an infrequent phenomenon that may involve an unusual set of circumstances. Each one of the products of zonal raciation has the potential to become a new species and by having more races increases the chance of a speciation event.

Segregation and fertility in Mus musculus domesticus (wild mice) heterozygous for the Rb(4.12) translocation

Analysis of the progeny of wild mice heterozygous for the Rb(4.12) shows that fertility and segregation are normal. This study, and others with similar results, suggests that our view of the chromosomal evolution of the house mouse should be revised.

A hybrid zone comprising staggered chromosomal clines in the house mouse (Mus musculus domesticus)

In the vicinity of John o'Groats (Caithness, Scotland) there is a small karyotypic race of the house mouse (Mus musculus domesticus) characterized by a diploid number of 32 chromosomes, including the metacentrics 4.10, 9.12, 6.13 and 11.14. This race forms a hybrid zone with the standard British race (fully acrocentric chromosomes, 2n = 40). Although hybrid zones normally consist of several (or many) narrow character clines at the same position, this zone is unusual in that the chromosomal clines do not coincide. The cline for arm combination 11.14 is staggered relative to the 6.13 cline and both are separate from the clines for 4.10 and 9.12 (which may or may not coincide). A variety of explanations for the structure of the hybrid zone are discussed. It is possible that this may be a case of 'zonal raciation'.

Antibody repertoire against culture filtrate antigens in wild house mice infected with Mycobacterium bovis BCG

Wild house mice (Mus domesticus) captured in a Flemish pigsty were infected intravenously with 4 x 10(6) variable units of Mycobacterium bovis BCG and examined by Western blot analysis for IgG secretion against BCG culture filtrate (CF) antigens. Wild mice showed a marked individual variation in antibody pattern when tested 4, 6 and 8 weeks after infection. Some animals reacted to a wide range of antigens and others only to a limited number. Most wild mice recognized preferentially antigens with molecular weight of 24 kD, 32 kD, 37-38-40 kD, 65 kD and 82 kD, i.e. the major CF antigens known to be recognized by sera from BCG-infected inbred laboratory strains, BALB/c, DBA/2, CBA/Ca and C57BL/6. The 32-kD fibronectin-binding protein and the 65-kD heat-shock protein appeared as very immunodominant in wild mice. Furthermore, about 20-25% of the mice reacted strongly with a unique antigen of 35 kD estimated molecular weight, to which the tested inbred laboratory mice did not respond. Monitoring the size of the bacterial population in the spleen indicated that the BCG inoculum did not replicate in wild mice, suggesting that the Bcgr allele is expressed in this population.