Evolutionary Genomics of Plant Adaptation and Speciation

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Recombination plays a central role in how new species arise. Three evolutionary forces (selection, mutation, and genetic drift) create differences between populations, while two other forces (gene flow and recombination) homogenize them. Evolutionary biologists have long recognized this antagonism, leading many to question the likelihood of speciation in the absence of geographic barriers to mating between diverging populations. However, in recent decades, speciation with gene flow has received both theoretical and empirical support. One emerging theme is the evolution of mechanisms that suppress recombination between genes underlying local adaptation and/or reproductive isolation. Here, I propose to leverage genomic and germplasm resources for sunflower to test fundamental hypotheses regarding the origin, establishment, and evolutionary role of recombination suppressors. First, I will investigate the genomic basis of polymorphic recombination cold spots. This will allow me to test theoretical predictions regarding how different recombination suppressors contribute to ecological divergence and speciation, as well as to explore parallels between the evolution of recombination cold spots on autosomes versus sex chromosomes. Second, I will determine the mechanisms by which such regions become established. Models of divergence with gene flow typically assume that recombination suppression evolves to reduce recombination between locally adapted alleles. However, recombination modifiers (e.g., chromosomal inversions) might spread for other reasons, including direct selection on inversion breakpoints or due to chance events in small populations (genetic drift). Third, I will search for associations between these regions and traits that cause individuals to preferentially mate with others in the same population (i.e., assortative mating). Such associations are predicted to facilitate speciation with gene flow. Overall, this work will help define the role of recombination suppressors in plant adaptation and speciation. Also, a better understanding of the recombination landscape in sunflower will facilitate breeding programs in this important oilseed crop. Additional benefits to Canada will accrue from the training of highly qualified personnel in ecological genetics, genomics, and bioinformatics.