Development of unique house mouse resources suitable for evolutionary studies of speciation

Two house mouse subspecies, Mus musculus domesticus and Mus musculus musculus, form a hybrid zone in Europe and represent a suitable model for inferring the genes contributing to isolation barriers between parental taxa. Despite long-term intensive studies of this hybrid zone, we still know relatively little about the causes and mechanisms maintaining the 2 taxa as separate subspecies; therefore, to gain insight into this process, we developed 8 wild-derived inbred house mouse strains. In order to produce strains as pure domesticus or musculus genomes as possible, the individuals used to establish the breeding colony for the 3 domesticus and 2 of the musculus strains were captured in the Czech Republic from wild populations at extreme western and eastern edges of the subspecific contact zone, respectively. The remaining 3 musculus strains were bred from mice captured about 250 km east of the hybrid zone. Genetic analysis based on 361 microsatellite loci showed that 82% of these markers are diagnostic for either the musculus or the domesticus strains. In order to demonstrate the potential utility of this genetic differentiation in such strains, phenotypic variation was scored for 2 strains from opposite edges of the hybrid zone and significant differences in morphology, reproductive performance, in vitro immune responses, mate choice based on urinary signals, and aggressiveness were found. In addition, the 3 strains derived from musculus populations far from the hybrid zone display significant differences in polymorphism in hybrid male sterility when crossed with the laboratory strains C57BL/6 or C57BL/10, which have a predominantly domesticus genome. Although further studies will be necessary to demonstrate intersubspecific differences, all analyses presented here indicate that these newly developed house mouse strains represent a powerful tool for elucidating the genetic basis of isolation barriers in hybrid zones and for studying speciation in general.