Hybridization and Introgression Associated With Range Expansion and Invasion In Sunflowers

We tested the hypothesis that hybridization with close relatives is more common in the invasive than native range of a species by quantifying the level of introgression in multiple independently-derived invasive and weedy sunflower (Helianthus annuus) lineages in Europe, Asia, and Australia, and recent range expansions in North America. In the ancestral native range, hybridization was detected between wild and domesticated sunflowers, but the level of admixture was low. However, hybridization has a more marked effect on genomic composition outside of the native range: non-native lineages had higher frequencies of alleles derived from hybridization and a higher proportion of their genome derived from introgression. The parallel incidence of high rates of introgression in multiple independent invasive and weedy sunflower lineages supports the importance of hybridization in the during the evolution of invasive populations. This may be due to selection favoring new allele combinations, relaxed barriers to gene flow, higher exposure to gene flow, or a combination of these factors.