The world is full of species. The number and variety of species is a balance between extinction (loss of species) and speciation (formation of species). A powerful strategy for understanding the origin of species is to examine the evolution of reproductive barriers and how these barriers are inherited. By studying hybrids in nature and in the lab from genetic and genomic perspectives, we are learning about how one species becomes two.
Locating Hybrid Incompatibilities in the Genome
Certain combinations of genes reduce the fitness of hybrids between nascent species. We found that selection against these incompatibilities leaves a signature in sequence variation that can be used to locate them in the genome. We developed a method for this purpose, which we are applying to a natural hybrid zone between two lineages of house mice.
Genomic Ancestry of Wild Hybrids
Moving along a chromosome in a hybrid, the ancestry alternates between species 1 and species 2. The placement and number of junctions between ancestries are sensitive indicators of the history of hybridization. Applying this logic to wild hybrids of house mice, we reconstructed a rich genomic tapestry of hybridization that is helping us uncover the dynamics of genetic mixing in nature.
Genetics of Hybrid Sterility
Many pairs of species produce hybrids that are viable but less fertile. Hybrid sterility is therefore a common reproductive barrier between species that often plays an important role in species formation. We identified genomic regions that shift cell populations and distort gene expression in the testes of house mouse hybrids. We are determining whether these genomic regions decrease gene flow between lineages of house mice in nature.