Recombination and Speciation in the Annual Sunflowers

In sexual species, recombination is considered to be the greatest impediment to speciation. The main problem with recombination is that although divergent selection favors the buildup of associations between alleles favored in local environments and those causing reproductive isolation, gene flow and recombination break the associations apart. However, examples of speciation in the face of gene flow began accumulating in the late 20th century, with accelerating evidence over the past two decades. How can this happen? In my talk, I will attempt to answer this question, drawing on a series of investigations of wild sunflower species, ranging from genome-wide association studies of phenotypic variation to field-based analyses of reproductive barrier strength, to functional characterization of candidate genes underlying reproductive isolation. I will show that most of the traits and genes that contribute to local adaptation and reproduction isolation in wild sunflowers are associated with chromosomal inversions or other recombination suppressors, thereby resolving the antagonism between selection and recombination. This genetic architecture appears to be common in other organisms, and thus offers a general solution for how speciation can occur in the presence of gene flow.