1. 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.2. 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.3. 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. K E Y W O R D SAFLP, Brassicaceae, Bunias orientalis, chemical diversity, genetic diversity, glucosinolates, herbivore performance, invasion ecology, metabolomics | 715Journal of Ecology TEWES ET al.

Various mechanisms can facilitate the success of plant invasions simultaneously, but may be difficult to disentangle. In the present study, plants of the range-expanding species Bunias orientalis from native, invasive and naturalised, not yet invasive populations were compared in a field common garden over two years. Plants were grown under two nitrate-regimes and multiple traits regarding growth, defence, antagonist loads and reproduction were measured. A rank-based clustering approach was used to assign correlated traits to distinct suites. These suites were analysed for “syndromes” that are expressed as a function of population origin and/or fertilisation treatment and might represent different invasion mechanisms. Indeed, distinct suites of traits were differentially affected by these factors. The results suggest that several pre-adaptation properties, such as certain growth characteristics and intraspecific chemical variation, as well as post-introduction adaptations to antagonists and resource availability in novel habitats, are candidate mechanisms that facilitate the success of invasive B. orientalis in parallel. It was concluded that rank-based clustering is a robust and expedient approach to integrate multiple traits for elucidating invasion syndromes within individual species. Studying a multitude of traits at different life-history and establishment stages of plants grown under distinct resource treatments reveals species-specific trade-offs and resource sinks and simplifies the interpretation of trait functions for the potential invasive success of plants.

Chemical defense is a widespread anti-predator strategy exhibited by organisms, with individuals either synthesizing or extrinsically acquiring defensive chemicals. In some species, such defences can also be transferred among conspecifics. Here, we tested the effects of pharmacophagy on the defense capability of the turnip sawfly, Athalia rosae , which can acquire neo -clerodane diterpenoids (clerodanoids) via pharmacophagy when having access to the plant Ajuga reptans. We show that clerodanoid access mediates protection against predation by mantids for the sawflies, both in a no-choice feeding assay and a microcosm setup. Even indirect access to clerodanoids, via nibbling on conspecifics that had access to the plant, resulted in protection against predation albeit to a lower degree than direct access. Furthermore, sawflies that had no direct access to clerodanoids were consumed less frequently by mantids when they were grouped with conspecifics that had direct access. Most, but not all, of such initially undefended sawflies could acquire clerodanoids from conspecifics that had direct access to the plant, although in low quantities. Together our results demonstrate that clerodanoids serve as a chemical defense that can also be transferred by interactions among conspecifics. Moreover, the presence of chemically defended individuals in a group can confer protection onto conspecifics that had no direct access to clerodanoids.

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Within several plant species, a high variation in the composition of particular defence metabolites can be found, forming distinct chemotypes. Such chemotypes show different effects on specialist and generalist plant enemies, whereby studies examining interactions with pathogens are underrepresented. We aimed to determine factors mediating the interaction of two chemotypes of Bunias orientalis (Brassicaceae) with two plant pathogenic fungal species of different host range, Alternaria brassicae (narrow host range = specialist) and Botrytis cinerea (broad hostrange = generalist) using a combination of controlled bioassays. We found that the specialist, but not the generalist, was sensitive to differences between plant chemotypes in vivo and in vitro. The specialist fungus was more virulent (measured as leaf water loss) on one chemotype in vivo without differing in biomass produced during infection, while extracts from the same chemotype caused strong growth inhibition in that species in vitro. Furthermore, fractions of extracts from B. orientalis had divergent in vitro effects on the specialist versus the generalist, supporting presumed adaptations to certain compound classes. This study underlines the necessity to combine various experimental approaches to elucidate the complex interplay between plants and different pathogens. Plants produce a multitude of defensive compounds that mediate interactions with attacking organisms from different taxa 1. Generalists may be fended-off by (sets of) defence compounds effectively, while specialists instead use such compounds as host selection cues 2,3. These distinct roles of individual compounds in interactions with different natural enemies, including herbivores and pathogens, is discussed to be one of the major drivers of the evolution of diverse plant defences 4-6. A high variation in chemical defence profiles can be particularly found within plant species, in which so-called chemotypes are formed, that differ in the composition of a certain metabolite class 7-10. Several studies address the responses of insect herbivores to distinct chemical defence profiles in plant families or species 8,11,12. In contrast, only little is known about the role of phytochemical variation in interactions with pathogens (but see, e.g. 7). Various plant species of the Brassicaceae family show different chemotypes and are well-studied for interactions of certain chemotypes with plant enemies. For example, distinct chemotypes have been found in Arabidopsis thaliana 13,14 , Barbarea vulgaris 10,15 and Brassica oleracea 16,17. Interestingly, in B. vulgaris one chemotype is resistant to two herbivore species, while another is instead resistant to an oomycete pathogen 18 , underlining the importance to consider enemies from different taxa in chemo-ecological studies. Chemotypes in the Brassicaceae are typically characterised by variations in profiles of glucosinolates, a structurally highly diverse group of defence compounds 19. Glucosinolates are assumed to be largely involved in resistance of ...