Geographic population structure in an outcrossing plant invasion after centuries of cultivation and recent founding events

Authors: Gaskin, John; SHWARZLAENDER, MARK - University Of Idaho; GIBSON, ROB - University Of Idaho; SIMPSON, HEATHER - University Of New Mexico; MARSHALL, DIANE - University Of New Mexico; GERBER, ESTHER - Commonwealth Agricultural Bureau International (CABI) - Switzerland; HINZ, HARIET - Commonwealth Agricultural Bureau International (CABI) - Switzerland

Submitted to: AoB Plants
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/12/2018
Publication Date: 3/13/2018
Citation: Gaskin, J.F., Shwarzlaender, M., Gibson, R., Simpson, H., Marshall, D.L., Gerber, E., Hinz, H. 2018. Geographic population structure in an outcrossing plant invasion after centuries of cultivation and recent founding events. AoB Plants. 10(2):ply020. https://doi.org/10.1093/aobpla/ply020.
DOI: https://doi.org/10.1093/aobpla/ply020

Interpretive Summary: We investigated the genetic diversity and origins of a long-term cultivar. Dyer’s woad (Isatis tinctoria L.; Brassicaceae) that has been used as a dye source for at least eight centuries in Eurasia. It was then introduced to eastern USA in the 1600s, and is now considered invasive in the western USA. Our genetic analysis of 645 plants from the USA and Eurasia suggest that there are two distinct invasions in western USA. We found that our two western USA invasions most likely originated from Switzerland, Ukraine and Germany. Genetic information assists in efforts to manage invasive species, and continued combination of ecological and molecular data will help bring us closer to sustainable management of plant invasions.

Technical Abstract: Population structure and genetic diversity of invasions are the result of evolutionary processes such as natural selection, drift, and founding events. Some invasions are also molded by additional human activities such as selection for cultivars and intentional introduction of desired phenotypes, which can lead to low genetic diversity in the resulting invasion. We investigated the population structure, diversity and origins of a species with both accidental and intentional introduction histories, as well as long-term selection as a cultivar. Dyer’s woad (Isatis tinctoria L.; Brassicaceae) has been used as a dye source for at least eight centuries in Eurasia, was introduced to eastern USA in the 1600s, and is now considered invasive in the western USA. Our analyses of AFLPs (Amplified Fragment Length Polymorphisms) from 645 plants from the USA and Eurasia suggest that there are two distinct invasions in western USA, with lower total gene diversity (Ht) and genetic differentiation (Fst) in the invasion than the native range, but higher gene diversity (Hj [=He]) than expected in the invasion. Though our sampling of Asian plants was limited, we found that our two western USA invasions most likely originated from Switzerland, Ukraine and Germany. This study highlights the effect of multiple evolutionary processes over centuries can have on population structure and diversity, though we found a higher than expected genetic diversity and lower population differentiation than expected in the invasion. Genetic information on population structure, diversity and origins assists in efforts to manage invasive species, and continued combination of ecological and molecular data will help bring us closer to sustainable management of plant invasions.