Intracontinental plant invader shows matching genetic and chemical profiles and might benefit from high defence variation within populations

Whereas many studies have revealed mechanisms driving plant invasions between continents, research on intracontinental range expanders is scarce. Therefore, we studied genetic, chemical and ecological traits of a range-expanding Brassicaceae, assuming that high genetic diversity should maintain chemical variation, which potentially benefits the invasion success. Moreover, we expected that within-individual defence diversity plays an essential role in biotic interactions. We compared Bunias orientalis L. plants from 16 populations of native, invasive or exotic non-invasive origin. The genetic structure was investigated by analysing the plastid DNA and amplified fragment length polymorphisms. For characterisation of the leaf chemistry, metabolic fingerprinting and profiling of glucosinolates as defence compounds were performed. The plant defence potential was tested using the generalist herbivore Mamestra brassicae. We found two major genetic lineages, which were mirrored in distinct chemical fingerprints of the plants. Genetic differentiation patterns point to a multiple introduction history of B. orientalis underlying the range expansion. Moreover, the genetic distance between individuals was correlated with the distance in chemical features. Genetic diversity tended to be reduced in potential leading edge (exotic) populations and was positively associated with quantitative metabolic diversity. Concentrations of indole glucosinolates were elevated in non-native populations, and high glucosinolate diversity was associated with low herbivore survival. Synthesis. This study suggests that the invasion success of this species may be facilitated by high chemical variation within populations. Moreover, high defence diversity within individuals of a population might be the main factor reducing herbivory and can be more important than the total concentration of defences. The combination of genetic and chemical analyses combined with bioassays revealed to be a powerful tool to study the differentiation between native and non-native populations and should be applied more often to explore intraspecific divergence.