Gene Flow and Ancestry in Clarkia Xantiana
Even after substantial divergence, gene flow can occur between plant subspecies coming back into sympatry. Genomic evidence suggests that this is common, and understanding how (sub)species remain distinct from each other even after coming into contact is a major goal of speciation research. We studied two subspecies of Clarkia xantiana flowers living sympatrically in Southern California and used a Hidden Markov Model to quantify ancestry across the genome of 368 plants (approximately 180 of each subspecies) living in three different sympatric sites: how much of one subspecies is in the genome of the opposite subspecies. In these sympatric populations, outcrossers incorporated more genes from selfing plants than vice versa. Additionally, gene flow levels were higher in some sites than in others and varied within sites. This indicates that gene flow is not symmetric and depends on aspects of the environment and characteristics of the plants. Quantifying variability in gene flow will contribute to our understanding of how subspecies can persist while exchanging genes in sympatry.