Print PageThe profusion of invasive hybrid lineages suggests that hybridization may facilitate invasion by promoting rapid evolution of novel weedy phenotypes, but comparative data on the rate and genomic extent of hybridization across both the native and invasive range of a species are lacking We tested the hypothesis that hybridization 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, Australia and North America, We used Illumina and 454 sequence to characterize variation in expressed protein-coding genes in 23 wild individuals from across the native range, 19 domesticated lines and 13 individuals from weedy and invasive populations. We identified regions of the genome that are highly divergent between domesticated and wild sunflowers, and show that weedy populations are derived from crop-wild hybridization. We also use coalescent-based likelihood methods to estimate rates of gene flow between crops and wild sunflowers in the native range as compared to in weedy and invasive populations.
Results/Conclusions
In the native range, hybridization was frequently 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 origins of invasive populations.
