Comparative Herbivory Rates and Secondary Metabolite Profiles in the Leaves of Native and Non-Native Lonicera Species

Metabolome expression in Eucryphia cordifolia populations: Role of seasonality and ecological niche centrality hypothesis

The ecological niche centrality hypothesis states that population abundance is determined by the position in the ecological niche, expecting higher abundances towards the center of the niche and lower at the periphery. However, the variations in the conditions that favor the persistence of populations between the center and the periphery of the niche can be a surrogate of stress factors that are reflected in the production of metabolites in plants. In this study we tested if metabolomic similarity and diversity in populations of the tree species Eucryphia cordifolia Cav. vary according to their position with respect to the structure of the ecological niche. We hypothesize that populations growing near the centroid should exhibit lower metabolites diversity than plants growing at the periphery of the niche. The ecological niche of the species was modeled using correlative approaches and bioclimatic variables to define central and peripheral localities from which we chose four populations to obtain their metabolomic information using UHPLC-DAD-QTOF-MS. We observed that populations farther away from the centroid tend to have higher metabolome diversity, thus supporting our expectation of the niche centrality hypothesis. Nonetheless, the Shannon index showed a marked variation in metabolome diversity at the seasonal level, with summer and autumn being the periods with higher metabolite diversity compared to winter and spring. We conclude that both the environmental variation throughout the year in combination with the structure of the ecological niche are relevant to understand the variation in expression of metabolites in plants.

The First Evidence of Gibberellic Acid's Ability to Modulate Target Species' Sensitivity to Honeysuckle (Lonicera maackii) Allelochemicals

Invasive species employ competitive strategies such as releasing allelopathic chemicals into the environment that negatively impact native species. Decomposing Amur honeysuckle (Lonicera maackii) leaves leach various allelopathic phenolics into the soil, decreasing the vigor of several native species. Notable differences in the net negative impacts of L. maackii metabolites on target species were argued to depend on soil properties, the microbiome, the proximity to the allelochemical source, the allelochemical concentration, or environmental conditions. This study is the first to address the role of target species' metabolic properties in determining their net sensitivity to allelopathic inhibition by L. maackii. Gibberellic acid (GA₃) is a critical regulator of seed germination and early development. We hypothesized that GA₃ levels might affect the target sensitivity to allelopathic inhibitors and evaluated differences in the response of a standard (control, Rbr), a GA₃-overproducing (ein), and a GA₃-deficient (ros) Brassica rapa variety to L. maackii allelochemicals. Our results demonstrate that high GA₃ concentrations substantially alleviate the inhibitory effects of L. maackii allelochemicals. A better understanding of the importance of target species' metabolic properties in their responses to allelochemicals will contribute to developing novel invasive species control and biodiversity conservation protocols and may contribute to applications in agriculture.

Interactions With Plant Defences Isolate Sympatric Populations of an Herbivorous Mite

Host plant specialisation can promote evolutionary divergence between herbivore populations associated with different plant species. While the mechanisms by which specialist species exploit their hosts have been studied widely across taxa, less is known about the mechanisms that allow intraspecific variants to arise and to be maintained across spatial and temporal scales. To understand whether adaptations to plant defences against herbivory contribute to the co-existence of genetically distinct populations of an herbivore, we investigate the interaction between honeysuckle (Lonicera periclymenum) and sympatric specialist and generalist populations of the spider mite Tetranychus urticae. We found that mite folivory induces the production of sticky droplets on honeysuckle, which have a defensive role: they increase mite mortality directly, and potentially indirectly by increasing the arrestment of a predator. We show that droplet induction and the preference to feed on honeysuckle depend on mite genotype, where the generalist avoids this host and the specialist suppresses droplet production. These traits are heritable and dominant in F1 hybrids between generalists and specialists. Selection pressure from honeysuckle and differences in host preference likely reduce the opportunity of mating encounters on this host. We propose that the interplay between selection from host plant defences and ecological barriers to hybridisation contribute to the persistence of genetically distinct populations of a single species in sympatry.

The many dimensions of phytochemical diversity: linking theory to practice

Research on the ecological and evolutionary roles of phytochemicals has recently progressed from studying single compounds to examining chemical diversity itself. A key conceptual advance enabling this progression is the use of species diversity metrics for quantifying phytochemical diversity. In this perspective, we extend the theory developed for species diversity to further our understanding of what exactly phytochemical diversity is and how its many dimensions impact ecological and evolutionary processes. First, we discuss the major dimensions of phytochemical diversity - richness, evenness, functional diversity, and alpha, gamma and beta diversity. We describe their potential independent roles in biotic interactions and the practical challenges associated with their analysis. Second, we re-analyse the published and unpublished datasets to reveal that the phytochemical diversity experienced by an organism (or observed by a researcher) depends strongly on the scale of the interaction and the total amount of phytochemicals involved. We argue that we must account for these frames of reference to meaningfully understand diversity. Moving from a general notion of phytochemical diversity as a single measure to a precise definition of its multidimensional and multiscale nature yields overlooked testable predictions that will facilitate novel insights about the evolutionary ecology of plant biotic interactions.