Deconstruction of a plant‐arthropod community reveals influential plant traits with nonlinear effects on arthropod assemblages

Evolutionary signatures of a trade-off in direct and indirect defenses across the wild grape genus, Vitis

Evolutionary correlations between chemical defense and protection by mutualist bodyguards have been long predicted, but tests of these patterns remain rare. We use a phylogenetic framework to test for evolutionary correlations indicative of trade-offs or synergisms between direct defense in the form of plant secondary metabolism and indirect defense in the form of leaf domatia, across 33 species in the wild grape genus, Vitis. We also performed a bioassay with a generalist herbivore to associate our chemical phenotypes with herbivore palatability. Finally, we tested whether defensive traits correlated with the average abiotic characteristics of each species' contemporary range and whether these correlations were consistent with plant defense theory. We found a negative evolutionary correlation between domatia size and the diversity of secondary metabolites in Vitis leaf tissue across the genus, and also that leaves with a higher diversity and richness of secondary metabolites were less palatable to a generalist herbivore, consistent with a trade-off in chemical and mutualistic defense investment. Predictions from plant defense theory were not supported by associations between investment in defense phenotypes and abiotic variables. Our work demonstrates an evolutionary pattern indicative of a trade-off between indirect and direct defense strategies across the Vitis genus.

Metabolomic Evenness Underlies Intraspecific Differences Among Lineages of a Wetland Grass

The metabolome represents an important functional trait likely important to plant invasion success, but we have a limited understanding of whether the entire metabolome or targeted groups of compounds confer an advantage to invasive as compared to native taxa. We conducted a lipidomic and metabolomic analysis of the cosmopolitan wetland grass Phragmites australis. We classified features into metabolic pathways, subclasses, and classes. Subsequently, we used Random Forests to identify informative features to differentiate five phylogeographic and ecologically distinct lineages: European native, North American invasive, North American native, Gulf, and Delta. We found that lineages had unique phytochemical fingerprints, although there was overlap between the North American invasive and North American native lineages. Furthermore, we found that divergence in phytochemical diversity was driven by compound evenness rather than metabolite richness. Interestingly, the North American invasive lineage had greater chemical evenness than the Delta and Gulf lineages but lower evenness than the North American native lineage. Our results suggest that metabolomic evenness may represent a critical functional trait within a plant species. Its role in invasion success, resistance to herbivory, and large-scale die-off events common to this and other plant species remain to be investigated.

Comparative assessment of satellite- and drone-based vegetation indices to predict arthropod biomass in shrub-steppes

Arthropod biomass is a key element in ecosystem functionality and a basic food item for many species. It must be estimated through traditional costly field sampling, normally at just a few sampling points. Arthropod biomass and plant productivity should be narrowly related because a large majority of arthropods are herbivorous, and others depend on these. Quantifying plant productivity with satellite or aerial vehicle imagery is an easy and fast procedure already tested and implemented in agriculture and field ecology. However, the capability of satellite or aerial vehicle imagery for quantifying arthropod biomass and its relationship with plant productivity has been scarcely addressed. Here, we used unmanned aerial vehicle (UAV) and satellite Sentinel-2 (S2) imagery to establish a relationship between plant productivity and arthropod biomass estimated through ground-truth field sampling in shrub steppes. We UAV-sampled seven plots of 47.6-72.3 ha at a 4-cm pixel resolution, subsequently downscaling spatial resolution to 50 cm resolution. In parallel, we used S2 imagery from the same and other dates and locations at 10-m spatial resolution. We related several vegetation indices (VIs) with arthropod biomass (epigeous, coprophagous, and four functional consumer groups: predatory, detritivore, phytophagous, and diverse) estimated at 41-48 sampling stations for UAV flying plots and in 67-79 sampling stations for S2. VIs derived from UAV were consistently and positively related to all arthropod biomass groups. Three out of seven and six out of seven S2-derived VIs were positively related to epigeous and coprophagous arthropod biomass, respectively. The blue normalized difference VI (BNDVI) and enhanced normalized difference VI (ENDVI) showed consistent and positive relationships with arthropod biomass, regardless of the arthropod group or spatial resolution. Our results showed that UAV and S2-VI imagery data may be viable and cost-efficient alternatives for quantifying arthropod biomass at large scales in shrub steppes. The relationship between VI and arthropod biomass is probably habitat-dependent, so future research should address this relationship and include several habitats to validate VIs as proxies of arthropod biomass.

Additive genetic effects in interacting species jointly determine the outcome of caterpillar herbivory

Plant-insect interactions are common and important in basic and applied biology. Trait and genetic variation can affect the outcome and evolution of these interactions, but the relative contributions of plant and insect genetic variation and how these interact remain unclear and are rarely subject to assessment in the same experimental context. Here, we address this knowledge gap using a recent host-range expansion onto alfalfa by the Melissa blue butterfly. Common garden rearing experiments and genomic data show that caterpillar performance depends on plant and insect genetic variation, with insect genetics contributing to performance earlier in development and plant genetics later. Our models of performance based on caterpillar genetics retained predictive power when applied to a second common garden. Much of the plant genetic effect could be explained by heritable variation in plant phytochemicals, especially saponins, peptides, and phosphatidyl cholines, providing a possible mechanistic understanding of variation in the species interaction. We find evidence of polygenic, mostly additive effects within and between species, with consistent effects of plant genotype on growth and development across multiple butterfly species. Our results inform theories of plant-insect coevolution and the evolution of diet breadth in herbivorous insects and other host-specific parasites.

A domestic plant differs from its wild relative along multiple axes of within-plant trait variability and diversity

For 10,000 years humans have altered plant traits through domestication and ongoing crop improvement, shaping plant form and function in agroecosystems. To date, studies have focused on how these processes shape whole-plant or average traits; however, plants also have characteristic levels of trait variability among their repeated parts, which can be heritable and mediate critical ecological interactions. Here, we examine an underappreciated scale of trait variation-among leaves, within plants-that may have changed through the process of domestication and improvement. Variability at this scale may itself be a target of selection, or be shaped as a by-product of the domestication process. We explore how levels of among-leaf trait variability differ between cultivars and wild relatives of alfalfa (Medicago sativa), a key forage crop with a 7,000-year domestication history. We grew individual plants from 30 wild populations and 30 cultivars, and quantified variability in a broad suite of physical, nutritive, and chemical leaf traits, including measures of chemical dissimilarity (beta diversity) among leaves within each plant. We find that trait variability has changed over the course of domestication, with effects often larger than changes in trait means. Domestic alfalfa had elevated among-leaf variability in SLA, trichomes, and C:N; increased diversity in defensive compounds; and reduced variability in phytochemical composition. We also elucidate fundamental relationships between trait means and variability, and between overall production of secondary metabolites and patterns of chemical diversity. We conclude that within-plant variability is an overlooked dimension of trait diversity in a globally critical agricultural crop. Trait variability is actually higher in cultivated plants compared to wild progenitors for multiple nutritive, physical, and chemical traits, highlighting a scale of variation that may mitigate loss of trait diversity at other scales in alfalfa agroecosystems, and in other crops with similar histories of domestication and improvement.

The Impact of Roads on the Redistribution of Plants and Associated Arthropods in a Hyper-Arid Ecosystem

The construction of vehicular roads likely affects the distribution of natural resources. Although the effects of roads on different ecosystem aspects have been extensively studied, studies in arid and, particularly, in hyper-arid ecosystems are scarce. In drylands, where water is the main limiting factor, the effect of roads on the redistribution of water may have strong subsequent effects on the ecosystem, especially when roads cross natural water flow paths. To fill this knowledge gap, we studied the effects of a road that runs across a slope on the distribution of plants and animals in a hyper-arid environment. Changes in shrub cover, below and above the road, were quantified by remote sensing and image classification, while plant-associated arthropods were vacuum-sampled from shrub canopies and from open (inter-shrub) areas. We found that the spatial distribution of shrubs, a vital resource facilitating many other organisms, was affected by the road, with an increase in the shrub cover immediately above the road and a decrease below it. Arthropod abundance generally followed shrub cover, but the exact pattern depended on the specific group sampled. While some arthropod groups (e.g., aphids, parasitic wasps and barklice) thrived under the disturbed conditions above the road, other arthropod groups (e.g., mites and true bugs) were less abundant in the disturbed patches. Our results highlight the strong effects of human-made structures on the distribution of flora and fauna in arid ecosystems.

Predicting patch occupancy reveals the complexity of host range expansion

Specialized plant-insect interactions are a defining feature of life on earth, yet we are only beginning to understand the factors that set limits on host ranges in herbivorous insects. To better understand the recent adoption of alfalfa as a host plant by the Melissa blue butterfly, we quantified arthropod assemblages and plant metabolites across a wide geographic region while controlling for climate and dispersal inferred from population genomic variation. The presence of the butterfly is successfully predicted by direct and indirect effects of plant traits and interactions with other species. Results are consistent with the predictions of a theoretical model of parasite host range in which specialization is an epiphenomenon of the many barriers to be overcome rather than a consequence of trade-offs in developmental physiology.

Caterpillars on a phytochemical landscape: The case of alfalfa and the Melissa blue butterfly

Modern metabolomic approaches that generate more comprehensive phytochemical profiles than were previously available are providing new opportunities for understanding plant-animal interactions. Specifically, we can characterize the phytochemical landscape by asking how a larger number of individual compounds affect herbivores and how compounds covary among plants. Here we use the recent colonization of alfalfa (Medicago sativa) by the Melissa blue butterfly (Lycaeides melissa) to investigate the effects of indivdiual compounds and suites of covarying phytochemicals on caterpillar performance. We find that survival, development time, and adult weight are all associated with variation in nutrition and toxicity, including biomolecules associated with plant cell function as well as putative anti-herbivore action. The plant-insect interface is complex, with clusters of covarying compounds in many cases encompassing divergent effects on different aspects of caterpillar performance. Individual compounds with the strongest associations are largely specialized metabolites, including alkaloids, phenolic glycosides, and saponins. The saponins are represented in our data by more than 25 individual compounds with beneficial and detrimental effects on L. melissa caterpillars, which highlights the value of metabolomic data as opposed to approaches that rely on total concentrations within broad defensive classes.

Plant functional diversity drives carbon storage following vegetation restoration in Loess Plateau, China

Ongoing climatic changes induced by human activities increases in atmospheric carbon dioxide (CO₂), which have considerable effects on the structure and function of ecosystems, including carbon (C) storage, plant functional traits and therefore on a wide set of ecosystem services. Plant functional diversity is benefit to improve plant photosynthesis and enhance C efficiency and therefore decrease CO₂. Here, the focus of this article is on integrating of plant functional diversity and C storage, which aims to contribute to C sequestration for climate change mitigation following vegetation restoration in Loess Plateau, China. Firstly, the CWM (plant community-weighted mean) traits of the most abundant plant species can account for C storage in AGBC (above-ground biomass C), ALC (above-ground litter C), STC (soil total carbon) and TEC (total ecosystem carbon). Secondly, the CWM of plant height and LCC (leaf carbon concentration) had a positive effect C storage in different part (AGBC, ALC, STC and TEC), while the CWM of LNC (leaf nitrogen concentration) and SLA (specific leaf area) had a negative effect on C storage in different part. Further, the CWM of plant height, LCC, SLA and plant functional dispersion (FDis) can be used to predict C storage by multiple linear regression analysis. Finally, the positive association between FDis and C storage was found in SEM, shedding light on the key role of plant functional diversity driving C storage following vegetation restoration. The findings presented here highlight the importance of both plant traits of dominant species and plant functional diversity in regulating C storage, and show that favorable climate conditions, particularly vegetation restoration, tend to increase C storage and plant functional diversity, which have important implications for improving global C cycling and ecosystem services.

Linking plant genes to insect communities: Identifying the genetic bases of plant traits and community composition

Community genetics aims to understand the effects of intraspecific genetic variation on community composition and diversity, thereby connecting community ecology with evolutionary biology. Thus far, research has shown that plant genetics can underlie variation in the composition of associated communities (e.g., insects, lichen and endophytes), and those communities can therefore be considered as extended phenotypes. This work, however, has been conducted primarily at the plant genotype level and has not identified the key underlying genes. To address this gap, we used genome-wide association mapping with a population of 445 aspen (Populus tremuloides) genets to identify the genes governing variation in plant traits (defence chemistry, bud phenology, leaf morphology, growth) and insect community composition. We found 49 significant SNP associations in 13 Populus genes that are correlated with chemical defence compounds and insect community traits. Most notably, we identified an early nodulin-like protein that was associated with insect community diversity and the abundance of interacting foundation species (ants and aphids). These findings support the concept that particular plant traits are the mechanistic link between plant genes and the composition of associated insect communities. In putting the "genes" into "genes to ecosystems ecology", this work enhances understanding of the molecular genetic mechanisms that underlie plant-insect associations and the consequences thereof for the structure of ecological communities.

The community and ecosystem consequences of intraspecific diversity: a meta-analysis

Understanding the relationships between biodiversity and ecosystem functioning has major implications. Biodiversity-ecosystem functioning relationships are generally investigated at the interspecific level, although intraspecific diversity (i.e. within-species diversity) is increasingly perceived as an important ecological facet of biodiversity. Here, we provide a quantitative and integrative synthesis testing, across diverse plant and animal species, whether intraspecific diversity is a major driver of community dynamics and ecosystem functioning. We specifically tested (i) whether the number of genotypes/phenotypes (i.e. intraspecific richness) or the specific identity of genotypes/phenotypes (i.e. intraspecific variation) in populations modulate the structure of communities and the functioning of ecosystems, (ii) whether the ecological effects of intraspecific richness and variation are strong in magnitude, and (iii) whether these effects vary among taxonomic groups and ecological responses. We found a non-linear relationship between intraspecific richness and community and ecosystem dynamics that follows a saturating curve shape, as observed for biodiversity-function relationships measured at the interspecific level. Importantly, intraspecific richness modulated ecological dynamics with a magnitude that was equal to that previously reported for interspecific richness. Our results further confirm, based on a database containing more than 50 species, that intraspecific variation also has substantial effects on ecological dynamics. We demonstrated that the effects of intraspecific variation are twice as high as expected by chance, and that they might have been underestimated previously. Finally, we found that the ecological effects of intraspecific variation are not homogeneous and are actually stronger when intraspecific variation is manipulated in primary producers than in consumer species, and when they are measured at the ecosystem rather than at the community level. Overall, we demonstrated that the two facets of intraspecific diversity (richness and variation) can both strongly affect community and ecosystem dynamics, which reveals the pivotal role of within-species biodiversity for understanding ecological dynamics.