Genetics of Speciation
The origin of new species is one of the most important and challenging problems in all of biology. Levels and patterns of biodiversity depend crucially on the process of speciation. Speciation can be viewed as the accumulation of reproductive barriers between populations. Therefore, studying the inheritance of traits that prevent interbreeding provides a powerful approach to understanding the origin of species. Recently, advances in genomics have been combined with this reasoning to yield clues about the genetic changes involved in speciation, including the identification of a few genes that cause sterility or death of hybrids in crosses between species pairs. This progress has catapulted speciation to the forefront of high-profile biological research, contributing to Science Magazine’s “breakthroughs of the year” in 2005 and 2006.
The best strategy for revealing the mechanism of speciation is to find the genetic changes that explain currently evolving reproductive barriers. Our laboratory uses the house mouse to find genes that contribute to speciation in action. The mouse is an especially powerful system because three recently evolved species exist, gene flow has been intensively studied in nature, and a plethora of genetic and genomic tools is available. We apply an integrated approach to understand the genetics of speciation. First, we associate genotypes with reproductive traits in mapping populations generated by species crosses between wild-derived inbred lines. In a novel scheme, we are mapping hybrid male sterility phenotypes, including sperm morphology, observed in crosses among three different species pairs. By combining QTL mapping with genome-wide inference of phylogenetic history, we aim to reconstruct the evolutionary history of mutations underlying speciation. In addition to unraveling the genetics of speciation, this research is directly relevant to human health. The mouse is the premier model organism for identifying and testing genes that cause male infertility in humans. Candidate genes have been identified through studies of mouse mutants, but the connection of these mutants to natural variation is unclear. Because our approach focuses on natural variation (similar to that observed in humans), the genes we identify could provide good candidate genes for sterility in human males.
Sperm from different species of house mice and their hybrids. Dom = Mus domesticus, Cast = M. castaneus, Musc = M. musculus.
Degenerated seminiferous tubules from a hybrid between different species of house mice.
Michael White is leading our research in this area.