Abstract
BackgroundWestern house mice Mus musculus domesticus are among the most important mammalian model species for chromosomal speciation. Hybrids between chromosomal races of M. m. domesticus suffer various degrees of fertility reduction between full fertility and complete sterility, depending on the complexity of the chromosomal differences between the races. This complexity presents itself in hybrids as meiotic configurations of chromosome chains and rings, with longer configurations having a stronger impact on fertility. While hybrids with short configurations have been intensively studied, less work has been done on hybrids with very long configurations. In this study, we investigated laboratory-reared wild mice from two chromosomally very different races in Switzerland found in close proximity. Hybrids between these races form a meiotic chain of fifteen chromosomes. We performed a detailed analysis of male and female hybrid fertility, including three generations of female backcrosses to one of the parental races. We also tested for possible divergence of mate preference in females.ResultsWhile all male F1 hybrids were sterile with sperm counts of zero, 48% of female F1 hybrids produced offspring. Their litter sizes ranged from one to three which is significantly lower than the litter size of parental race females. When hybrid females were backcrossed to a parental race, half of the offspring resembled the parental race in karyotype and fertility, while the other half resembled the F1 hybrids. In the preference test, females of both races indicated a lack of a preference for males of their own karyotype.ConclusionsAlthough the fertility of the F1 hybrids was extremely low because of the complexity of the chromosomal differences between the races, reproductive isolation was not complete. As we did not find assortative female preferences, we expect that contact between these races would lead to the production of hybrids and that gene flow would occur eventually, as fertility can be restored fully after one backcross generation.
Highlights
Western house mice Mus musculus domesticus are among the most important mammalian model species for chromosomal speciation
Speciation is a central topic in evolutionary biology [1], with a need for detailed studies of incipient reproductive isolation of major genetic forms within species through an analysis of hybridisation either in the laboratory or in nature, i.e. where the races make contact at hybrid zones [2]
We investigated the effect of chromosomal rearrangements, Robertsonian fusions, on the fertility of hybrids between two such genetic forms—chromosomal races—of house mice
Summary
Western house mice Mus musculus domesticus are among the most important mammalian model species for chromosomal speciation. We investigated laboratory-reared wild mice from two chromosomally very different races in Switzerland found in close proximity Hybrids between these races form a meiotic chain of fifteen chromosomes. Chromosomal rearrangements can suppress recombination and protect larger parts of the genome from introgression despite hybridisation, facilitating the accumulation of species-specific gene variants involved in Dobzhansky-Muller incompatibilities in these regions [6, 7]. Such incompatibilities may be related to mate choice
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