Syndromes in suites of correlated traits suggest multiple mechanisms facilitating invasion in a plant range-expander

Abstract

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.

Interactions of Bunias orientalis plant chemotypes and fungal pathogens with different host specificity in vivo and in vitro

“…A previous study suggested lower susceptibility of plants from the Turkish than of the German chemotype to unidentified pathogens when grown under field common garden conditions 25 . Contrasting findings in the present in vivo experiments may be partly related to the influence of mechanical leaf barriers that were to some extent reduced by pre-damaging the leaves prior to infection.…”

“…Compared to the control A. brassicae showed significant growth inhibition versus growth facilitation by metabolites present in leaf extracts from the Turkish versus the German chemotype. Regarding the invasion history of B. orientalis, such differences in chemical defence may have been shaped by random genetic drift after population founding 23 or by distinct selection pressures the plants experienced in their native (Turkish) versus the introduced (German) range 25 . A reduced pressure by different specialist enemies in novel habitats may have led to changes in the chemical defence composition in plants of the German population 44,45 .…”

“…Plants originated from a population in Turkey (T4; near Rize, 40° 44.33′ N, 40° 44.12′ E) and another in Germany (JE; Jena, 50° 52.42′ N, 11° 44.76′ E), here termed 'Turkish' and 'German' chemotype. Populations were chosen as representatives of their chemotype groups and as they exhibited the highest differences in infection by pathogens in previous field observations 25 . Per chemotype, a total of 30 seedlings were germinated and used for the experiments.…”

“…The Brassicaceae Bunias orientalis L. harbours two distinct genetic lineages, which represent two distinct chemotypes, that differ in their glucosinolate profiles and other polar metabolites 23 , as well as in susceptibility to plant enemies [23][24][25] . Plants from one chemotype, collected in the Caucasus region where the species potentially originates 26 , showed lower abundance of various herbivores and pathogens in a field common garden and were of lower host quality for a generalist herbivore in a laboratory experiment than plants of another chemotype, which was collected in the species' invasive range in northern parts of Eurasia 23,25 . However, it is unclear whether differences in pathogen infection spot abundance ultimately represent the impact of infection on the plants and whether chemotype susceptibility of B. orientalis differs in dependence of the degree of host specificity of the pathogens.…”

From plants to herbivores: novel insights into the ecological and evolutionary consequences of plant variation

“…Micro-or macro-scale spatial heterogeneity in the abiotic and biotic environment can generate significant within-and among-plant variation (e.g., Schaeffer et al 2018), and recent studies have provided novel insights into how plant chemistry impacts herbivores, microbes and natural enemies (Albrectsen et al 2018;Calf et al 2018;Coley et al 2018;Cuny et al 2018). Moreover, the effects of plant chemical traits are often considered in isolation, but they may act together with other features of growth and defense to form distinct trait combinations or syndromes (Coley et al 2018;Kergunteuil et al 2018;Tewes and Müller 2018). Yet it is important not to just focus on plant traits, as environmental change such as habitat fragmentation and climate change also alter the relative abundances of herbivores and predators (van der Putten 2012;Genua et al 2017).…”