Unravelling the genetic makeup of hybrid meadow knapweed populations in North America

Hybridization is thought to be a primary trigger of plant invasions, due to short term hybrid vigour of early generations or increased evolutionary potential in later generations. Yet despite widespread appreciation of the link between hybridization and invasion, few studies have actually tested whether hybridization during invasion reflects short-term vs. advanced generations of introgression. One of the main reasons for this is that identifying hybrids and differentiating them from their parental species presents formidable challenges.

Flowers of brown knapweed (Centaurea jacea), one of the parental species of the meadow knapweed hybrid. Image credit: Uoaei1 / Wikipedia

In a recent Editor’s Choice paper published in AoBP, Lachmuth et al. present a multifaceted analysis of the invasive meadow knapweed complex that unravels the genetic makeup of hybrid populations in North America. Meadow knapweed is a fertile hybrid between C. jacea (brown knapweed) and C. nigra (black knapweed), capable of freely backcrossing with either parental species. Despite their relevance as noxious weeds in the USA, members of this hybrid complex have only previously been studied in Europe where it is native, and not in North America where it is invasive. Lachmuth et al. use DNA sequencing to infer the genomic ancestry of individuals, and associate ancestry with variation in floral traits and genome size.  They find extensive genomic evidence of hybridisation, with significant but incomplete correspondence with floral traits and genome size.  These results highlight the widespread yet often cryptic nature of hybridization in plant invasions. The authors state, “The fact that plant species are transported globally with increasing frequency will lead to continued introduction of invasive hybrids to new regions as well as to the formation of novel hybrid taxa”. This suggests the link between hybvridisation and invasion success is likely to remain a critical issue for conservation of native species as well as fundamental to invasion and eco-evolutionary research.

Researcher highlight

Susanne Lachmuth holds a Ph.D. in Ecology from the University of Potsdam, Germany, and was an assistant professor in Plant Ecology at Martin Luther University Halle Wittenberg, where she completed her habilitation in August 2019. In 2017, she visited Prof. Steve Keller’s lab at The University of Vermont to acquire bioinformatics and genomics skills in the meadow knapweed project. Soon she will join the Global Change & Biodiversity lab (Prof. Matt Fitzpatrick) at the University of Maryland Center for Environmental Science.

The focus of Susanne’s research lies on ecological processes and contemporary evolution in natural populations of declining and invasive plants under anthropogenic environmental change. She implements research across the multiple scales from genetic variation to population and range dynamics and applies a variety of methods including population genetics, field surveys, common-garden, climate chamber and breeding experiments as well as ecological modelling.

Further reading

Lachmuth, S., Molofsky, J., Milbrath, L., Suda, J., & Keller, S. R. (2019). Associations between genomic ancestry, genome size and capitula morphology in the invasive meadow knapweed hybrid complex (Centaurea × moncktonii) in eastern North America. AoB PLANTS, 11(5). https://doi.org/10.1093/aobpla/plz055