Abstract
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.
Highlights
When races are in contact and hybridising, the geographic area where hybrids are found is known as a ‘hybrid zone’ [1]
The above survey of staggered hybrid zones in the house mouse indicates a variety of different hybrid zone structures and a various modes of origin
Hybrid zones examined by other researchers reinforce what we have described: In Belgium the BBEL race characterised by 4.12 and 5.10, in Germany the DSTJ race with 5.15 and
Summary
When races are in contact and hybridising, the geographic area where hybrids are found is known as a ‘hybrid zone’ [1]. There is a third way to have staggered clines: that is within a single locus, if a new allele arises within the hybrid zone and increases to high frequency (Figure 2) This could be a reticulation event in the sense that it happens after two races come into secondary contact, and the new allele could be a recombinant of alleles characterising the two races or could arise in relation to mutagenic processes associated with hybridisation. Metacentric mice and the standard acrocentric race in the vicinity of Barcelona are not distinguished by mitochondrial (mt) DNA or allozyme markers (Figure 3) This suggests, together with results from morphological data [21], that this is a primary contact; that a population near Barcelona accumulated metacentrics without a substantial period of geographic isolation and that the staggering of chromosomal clines may reflect some combination of time of formation of the metacentrics and the vagaries of population processes and genetic drift. There is a possibility that the non-coincidence of chromosomal clines in the John o’Groats-standard hybrid zone reflects a primary contact, and that the secondary contact is merely between the 36-chromosome form and the standard race
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
