The goal of the proposed research is to gain a better understanding of the demographics of hybrid speciation in the sunflower genus Helianthus. Three homoploid species were formed via hybridization between the same two parental species. It is thought that hybrid speciation in Helianthus may have been facilitated by founder events, but essentially nothing is known about the demography of hybrid speciation in these or other diploid hybrid species. The specific aims are to 1) use coalescent methods and many loci spread throughout the genome to estimate ancestral effective population sizes and population growth rates in the hybrid species to determine if they conform to expectations of a founder event speciation model; 2) determine levels of introgression between hybrid and parental species and test the hypotheses that introgression rates are correlated with varying selective forces and chromosomal rearrangements in various genomic regions; 3) perform phylogeographic studies of the parental species to test the hypothesis that the introduction of bison to North America contributed to hybrid speciation by increasing dispersal and the potential for isolation in unique habitats; and 4) perform phylogeographic studies of hybrid species to test for range expansion.