How do geography and natural selection shape genome-wide variation in the bush monkeyflower?
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A major goal of speciation research is to understand how genomic differences accumulate during the formation of new species, a process known as speciation. Early in the process, when isolating barriers are weak, only regions of the genome associated with isolating barriers are expected to diverge, while the rest of the genome is homogenized by gene flow. Thus, by identifying these differentiated regions, we may gain some insight into the genomic basis of reproductive isolation early in speciation. I used a genome scan approach to identify genomic regions that are highly diverged between red- and yellow-flowered ecotypes of the bush monkeyflower (Mimulus aurantiacus). The ecotypes, which are distributed in San Diego County, are partially reproductively isolated from one another by pollinator preferences despite ongoing gene flow between them. My genome-wide F¬ST analyses revealed a small number of genomic regions that are consistently differentiated between the ecotypes, suggesting that they are associated with pollinator isolation and speciation in this system.