A Genome-Wide Investigation of Factors Causing Postzygotic Isolation Between Two Mimulus Species.

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0075704WillisDarwin did not understand how reproductive barriers between new species could evolve. After all, it is hard to imagine how natural selection alone could regularly result in the evolution of maladaptive traits like the premature death or sterility of hybrid offspring. Today it is understood that chromosomal rearrangements (or underdominant loci) and epistatic interactions between loci can cause hybrid sterility. These alternatives invoke vastly different evolutionary processes, so differentiating between them is a fundamental step in understanding the origin of species. The proposed research will test for the action of chromosomal rearrangements and genetic interactions in causing the partial hybrid sterility observed in crosses between the wildflower species Mimulus guttatus and M. nasutus. The projects use mapped genetic markers to isolate chromosomal segments from each species in the heterospecific genomic background, and test their fitness in common garden experiments. The number, effects, patterns of expression, and genetic basis of individual incompatibility factors will be determined. These experiments address fundamental issues underlying the evolution of hybrid sterility, and so will contribute to our understanding of how new species originate.