Population Genomics of the Serpentine Sunflower, Helianthus bolanderi Using GBS

The serpentine sunflowers, Helianthus bolanderi and H. exilis, are close relatives and potential genetic resources for the domestic sunflower. They are known for their ability to colonize serpentine soil, which has an extremely low Ca/Mg ratio and high nickel levels. Furthermore, they are known to hybridize with the common sunflower, H. annuus. We used Genotyping-By-Sequencing on 221 samples to characterize the evolutionary history of H. bolanderi and H. exilis, their association with extreme soil, and introgression with H. annuus.

We found that the current species delimitations do not agree with genetic evidence. Both H. bolanderi and H. exilis samples grouped together genetically and the highest population structure corresponded to an east-west divide. Genetic evidence suggests they originated on serpentine soil and transitioned off multiple times. An ABBA-BABA test found evidence for gene flow with local H. annuus.