Patterns of introgression in the European house mouse hybrid zone: Comparisons among loci and between transects.

Abstract

Understanding the process by which populations become reproductively isolated from one another is a key component of understanding the process of speciation. Hybrid zones, where different taxa meet and produce at least some fertile offspring, provide an opportunity to study reproductive isolation in a system where the isolation is not complete. Through the study of differential patterns of introgression across a hybrid zone, it is possible to identify genetic factors that are involved in reproductive isolation. In this dissertation, a hybrid zone between the mice <italic>Mus domesticus</italic> and <italic> M. musculus</italic> is examined with the goal of identifying genomic regions involved in reproductive isolation between these taxa. Two different transects through this hybrid zone were utilized. Forty-eight molecular markers throughout the genome, fixed for different alleles in allopatric <italic>M. domesticus </italic> and <italic>M. musculus</italic> populations, were scored in the mice from both transects. The patterns of introgression across the hybrid zone were compared between the two transects, and among different markers. The patterns of introgression were found to be correlated between the two transects, indicating that these patterns are likely controlled by intrinsic forces, rather than local geography or random variation. There was strong variation in patterns of introgression among different markers. Introgression in the hybrid zone was found to be asymmetric, with <italic>M. domesticus </italic> alleles moving eastward into <italic>M. musculus</italic> at the majority of loci. The Y chromosome (paternally inherited) and mitochondria (maternally inherited) were found to have very different patterns of introgression in the hybrid zone. Possible explanations for this difference include sex-specific differences in behavior, or epistatic selection involving the Y chromosome. A locus on chromosome 17 is found to have limited introgression, relative to the rest of the chromosome. The region near this marker is proposed as a candidate region for reproductive isolation between <italic>M. domesticus </italic> and <italic>M. musculus</italic>. The work presented here suggests that there are many factors involved in the reproductive isolation of <italic> M. domesticus</italic> and <italic>M. musculus</italic>.