The role of hybridization for the invasion success of meadow knapweed Centaurea x moncktonii in North America
Evolution and Systematics of Plants and Fungi
Final Report Abstract
Biological invasions are a major threat for biodiversity and ecosystem functioning and at the same time excellent study systems for fundamental ecological and evolutionary research questions. Choosing the optimal management strategies requires a mechanistic understanding of the ecological and evolutionary processes underlying invasion dynamics and success. The project addressed inter-specific hybridization, genomic admixture and genome size variation as mechanisms that facilitate the evolution of traits that are indicative of invasiveness. The study system, the Centaurea jacea / nigra species complex, comprises the eponymous parental species and their hybrids (C. ×moncktonii C.E. Britton (meadow knapweed)), which all are native in Eurasia and invasive in North America. Meadow knapweed is spreading rapidly in a majority of the United States and has severe negative ecological and economic impact. We combined studies of genomic and quantitative trait variation in order to provide a first description of the genomic composition and taxonomic identity of populations of the C. jacea / nigra species complex in the Northeastern United States (New York State and Vermont). We clarified the relationships between genome size variation, taxonomic identity, genomic admixture and phenotypic traits indicative of invasiveness. The most important results so far can be summarized as follows: Numerous C. ×moncktonii hybrid populations are present, in particular in New York State, but also populations of the parental taxa continue to persist in the study region. Most admixed individuals were classified as F2 (or higher generation) hybrids. We found strong associations among genomic ancestry, genome size and morphology across all three taxa. However, hybrid populations expressed great variation in capitula traits and genome size in particular in advanced generation hybrids and back-crosses indicating transgressive trait segregation. Many hybrids exhibited a C. nigra - like floral morphology although the majority of them had higher genomic ancestry from the C. jacea - like parent, which may be explained by genetic drift or allelic dominance relationships. Advanced generation hybrids often had comparably small genome size possibly due to genomic rearrangements and genomic downsizing. Invasiveness traits varied among and within populations and stem width, above-ground biomass, time to flowering as well as the number of capitula increased significantly with the degree of genomic admixture. By contrast, no effects of genome size on phenotypic traits indicative of invasion success were found. The results provide a foundation for further exploration of the genomic consequences of hybridization as well as the genomic basis of adaptive evolution of invasiveness in the C. jacea / nigra species complex. Our findings advocate to focus management measures on eradicating highly admixed C. ×moncktonii populations, in particular in New York State, and on preventing continued hybridization among the parental taxa as well as back-crossing of hybrids to the parental taxa. Moreover, genome size should be considered as additional taxonomic characteristic for distinguishing the parental taxa also in Europe. Since species are transported globally with increasing frequency leading to continued introduction of invasive hybrids to new regions as well as to the formation of novel hybrid taxa, the hypothesized connection between genomic admixture and invasion success is likely to remain a critical issue for conservation of native species as well as fundamental invasion and eco-evolutionary research.
Publications
- (2017) The role of hybridization in the invasion success of meadow knapweed, Centaurea x moncktonii, in North America. Ecology Across Borders – Joint Annual Meeting of BES, GFÖ, necof and eef, Ghent, Belgium
Lachmuth S, Molofsky J, Suda J, Milbrath LR, Keller SR
