Effects Of Herbivory Research Articles

Density-Dependent Effects of Simultaneous Root and Floral Herbivory on Plant Fitness and Defense

Plants are attacked by multiple herbivores, and depend on a precise regulation of responses to cope with a wide range of antagonists. Simultaneous herbivory can occur in different plant compartments, which may pose a serious threat to plant growth and reproduction. In particular, plants often face co-occurring root and floral herbivory, but few studies have focused on such interactions. Here, we investigated in the field the combined density-dependent effects of root-chewing cebrionid beetle larvae and flower-chewing pierid caterpillars on the fitness and defense of a semiarid Brassicaceae herb. We found that the fitness impact of both herbivore groups was independent and density-dependent. Increasing root herbivore density non-significantly reduced plant fitness, while the relationship between increasing floral herbivore density and the reduction they caused in both seed number and seedling emergence was non-linear. The plant defensive response was non-additive with regard to the different densities of root and floral herbivores; high floral herbivore density provoked compensatory investment in reproduction, and this tolerance response was combined with aboveground chemical defense induction when also root herbivore density was high. Plants may thus prioritize specific trait combinations in response to varying combined below- and aboveground herbivore densities to minimize negative impacts on fitness.

Belowground crop responses to root herbivory are associated with the community structure of native arbuscular mycorrhizal fungi

There is growing interest in managing arbuscular mycorrhizal (AM) fungi in agriculture to support plant production. These fungi can support crop growth and nutrient uptake, but also affect plant-herbivore interactions. While our understanding of how AM fungi affect plant responses to herbivory advances, it is less clear how different naturally-occurring (native) fungal communities differentially influence crop responses to root-feeding insects.To explore this, plants (Sorghum bicolor) were grown in a glasshouse experiment without AM fungi (‘no AM fungi’) or with one of three natural soil inocula sourced either from a sclerophyll forest (‘forest inoculum’), a cropped field (‘field inoculum’), or a field in fallow (‘fallow inoculum’), while half the plants were subjected to a root herbivore (Dermolepida albohirtum). We assessed the effects of soil inoculum and root herbivory on root-colonising AM fungal diversity, plant growth, and nutrient content.Root herbivory did not affect AM fungal diversity or composition. Plants grown with the field or fallow inocula were both dominated by the genera Glomus and Claroideoglomus. These plants exhibited reduced biomass in response to inoculation, but were not impacted by root herbivory. In contrast, plants with the forest inoculum had AM fungal communities dominated by Paraglomus and Ambispora. When subjected to root herbivory, the forest inoculated plants and plants without AM fungi exhibited reductions of 44 % and 61 % in root biomass, and reductions of 65 % and 59 % in root phosphorus, respectively.Our study shows inoculation-driven plant responses to root herbivory that were associated with the community structure of their root-colonising AM fungi. Results suggest associations with communities dominated by Claroideoglomus and Glomus may mitigate the impacts of a root-feeding insect. More exploration of how natural assemblages of AM fungi mediate plant-herbivore interactions is needed if we are to effectively manage soil fungi in agriculture.

Herbivore damage and riparian shade constrain biomass distribution in American water willow (Justicia americana)

Emergent macrophytes can create important linkages between aquatic and terrestrial ecosystems. American water willow (Justicia americana) is an ecological engineer that provides structure and takes up nutrients in aquatic habitats but is subject to herbivory by terrestrial animals. Here, potential constraints that terrestrial herbivory, riparian shading, porewater nutrient stoichiometry, and co-occurrence with freshwater mussels may have on standing crops of aboveground and belowground water willow biomass were investigated across nine study sites in the Kiamichi River catchment, Oklahoma, USA. Stem damage – used to indirectly assess herbivore effects – and riparian shading were both associated with significant reductions in aboveground biomass. However, these variables were also somewhat correlated with each other, suggesting a possible interaction between shade and herbivory. Belowground biomass was more variable between sites than aboveground biomass, but the environmental variables that were sampled failed to explain this variation consistently. Because shadier water willow patches tend to have nutrient-richer tissues, we suggest that the correlation between riparian shade and herbivore damage may result from selective feeding by terrestrial herbivores at shadier sites. However, further experimental work (e.g., using grazing exclosures) is needed to assess this possibility due to the limitations of using stem damage counts as an indirect representation of herbivory. Despite these limitations, the present study complements a growing body of evidence that shows emergent macrophytes are seemingly more important as a resource for herbivores than historically recognized. Emergent macrophytes may be especially important when consumed by terrestrial herbivores that then transfer aquatic-derived resources into the terrestrial habitat. Data availabilityThe data used to generate this manuscript are available from the corresponding author upon reasonable request.

Insect exuviae as soil amendment affect flower reflectance and increase flower production and plant volatile emission.

Soil composition and herbivory are two environmental factors that can affect plant traits including flower traits, thus potentially affecting plant-pollinator interactions. Importantly, soil composition and herbivory may interact in these effects, with consequences for plant fitness. We assessed the main effects of aboveground insect herbivory and soil amendment with exuviae of three different insect species on visual and olfactory traits of Brassica nigra plants, including interactive effects. We combined various methodological approaches including gas chromatography/mass spectrometry, spectroscopy and machine learning to evaluate changes in flower morphology, colour and the emission of volatile organic compounds (VOCs). Soil amended with insect exuviae increased the total number of flowers per plant and VOC emission, whereas herbivory reduced petal area and VOC emission. Soil amendment and herbivory interacted in their effect on the floral reflectance spectrum of the base part of petals and the emission of 10 VOCs. These findings demonstrate the effects of insect exuviae as soil amendment on plant traits involved in reproduction, with a potential for enhanced reproductive success by increasing the strength of signals attracting pollinators and by mitigating the negative effects of herbivory.

Foliar herbivory affects the rhizosphere microbial assembly processes and association networks

Insect herbivores are prevalent in terrestrial ecosystems, and plants inevitably and continuously suffer damage by insect herbivores. Numerous studies have reported the effect of insect herbivory on plants; however, its effect on the belowground soil microbial community remains understudied. In the present study, using high-throughput sequencing, we investigated the effect of foliar insect herbivory on rhizosphere soil bacterial community. Our results showed that both herbivory intensity and duration after herbivory had no significant effect on the rhizosphere microbial community structure, but microbial assembly processes and association networks were strongly affected by the above two factors. Under moderate and high herbivory and at 6 weeks after herbivory, variable selection explained 55.56% and 51.52% of the community variation indicating that deterministic processes played a dominant role. Network complexity decreased from no herbivory (1.07) to high herbivory (0.97), and network complexity at 2 weeks after herbivory (0.92) was higher than that at 4 and 6 weeks after herbivory (0.79 and 0.84, respectively). The proportion of negative correlations decreased with increasing herbivory intensity and duration after herbivory. The number of keystone species decreased with increasing duration after herbivory but showed no change with increasing herbivory intensity. To our knowledge, this is among the first studies to illustrate the response mechanisms of rhizosphere microbial assembly processes and association networks to foliar herbivory. Our findings suggest that the assembly process and association network patterns of microbes are closely associated with herbivory intensity and duration after herbivory and enhance the understanding of insect-plant-soil microbe interactions.

Aboveground herbivory does not affect mycorrhiza-dependent nitrogen acquisition from soil but inhibits mycorrhizal network-mediated nitrogen interplant transfer in maize.

Arbuscular mycorrhizal fungi (AMF) are considered biofertilizers for sustainable agriculture due to their ability to facilitate plant uptake of important mineral elements, such as nitrogen (N). However, plant mycorrhiza-dependent N uptake and interplant transfer may be highly context-dependent, and whether it is affected by aboveground herbivory remains largely unknown. Here, we used 15N labeling and tracking to examine the effect of aboveground insect herbivory by Spodoptera frugiperda on mycorrhiza-dependent N uptake in maize (Zea mays L.). To minimize consumption differences and 15N loss due to insect chewing, insect herbivory was simulated by mechanical wounding and oral secretion of S. frugiperda larvae. Inoculation with Rhizophagus irregularis (Rir) significantly improved maize growth, and N/P uptake. The 15N labeling experiment showed that maize plants absorbed N from soils via the extraradical mycelium of mycorrhizal fungi and from neighboring plants transferred by common mycorrhizal networks (CMNs). Simulated aboveground leaf herbivory did not affect mycorrhiza-mediated N acquisition from soil. However, CMN-mediated N transfer from neighboring plants was blocked by leaf simulated herbivory. Our findings suggest that aboveground herbivory inhibits CMN-mediated N transfer between plants but does not affect N acquisition from soil solutions via extraradical mycorrhizal mycelium.

Long-term effects of herbivory on tree growth are not consistent with browsing preferences

Herbivores affect plants via direct consumption, but also indirectly via changes in the vegetation. These indirect effects may only manifest after decades of exposure and, as a result, their impact is rarely accounted for. To better understand the direct and indirect impacts of a large herbivore, moose ( Alces alces), on forests, we measured tree growth in areas that were both subjected to and excluded from herbivory for over 80 years. Growth data were gathered from five tree species, ranging from low to high palatability. We found that at small sizes, Betula papyrifera, a preferred species, benefited from herbivore exclusion. However, larger individuals grew more when exposed to herbivory, a response we attribute to lower competition in heavily browsed conditions. Populus tremuloides, a highly preferred tree, did not show any differences between levels of herbivory. Abies balsamea, a preferred winter browsed, was only marginally affected by browsing at smaller sizes. The two non-preferred species, Picea glauca and Picea mariana, did not show differential growth between herbivory levels. We conclude that herbivores can impact forests through both direct and indirect effects, that these effects are size specific, and that effects vary among species in ways not always predicted by consumption patterns.

Herbivore Influence on Post-Fire California Sage Scrub Plant and Soil Microbial Assemblages

California sage scrub (CSS) is an endangered, shrub-dominated, southern California ecosystem type threatened by increasing fire frequencies and conversion to non-native grasslands. As CSS harbors a rich endemic flora and fauna and is critical for maintaining key ecosystem services; significant attention has been focused on understanding how many key factors (N-deposition, drought, and competition with non-natives) influence post-fire CSS recovery. Unfortunately, few studies have examined the role of herbivores. For five years, we investigated the influence of herbivores on post-fire CSS succession by annually surveying plant assemblages in control (herbivores allowed access) and experimental (herbivore excluded) plots at the Bernard Field Station following a fire in May 2017. We found that herbivores reduce the cover of both invasive grasses and native shrubs, and negatively impact Artemisia californica survivorship. Consequently, post-fire plant restoration efforts should not discount the effects of herbivores. While native forb cover was elevated in plots that permitted herbivores, plots near the fire edge experienced increased herbivory pressure and lower cover of most plants. Despite modifications in plant assemblages, we did not observe differences in soil microbe abundances, fungi assemblage structure, or nutrient concentrations. We suggest that restoration practitioners consider caging ‘shrub regeneration’ areas to facilitate post-fire CSS recovery.

Shifting patch dynamics of floodplain woodlands in an arid savanna region: effects of soil form, flooding and large herbivores

• Monospecific woodland groves were associated with soil forms and flooding regimes in a floodplain. • Extreme floods removed trees and created substrates for woodland regeneration. • Damage by elephants and meso-browsers affected regeneration dynamics. • Flooding and herbivory interactively generated a shifting woodland mosaic anchored by soil. Our study addressed the regeneration dynamics of the patch mosaic of monospecific woodland groves in the floodplains of the Luvuvhu and Limpopo rivers following the removal of human settlements to create the Makuleke Contractual Park falling within the northern Kruger National Park. We anticipated that subsequent increases by elephants and meso-browsers like impalas would deflect or even prevent the re-establishment of these groves through the damage that they inflicted on plants. We compared the responses exhibited in groves of fever trees ( Vachellia xanthophloea ) associated with layered clay alluvium with those of ana trees ( Faidherbia albida ) associated with deep sandy deposits. Multi-decadal changes in the woodland mosaic were identified using aerial photographs and Google Earth imagery supported by onsite inspections and related to flood events and soil features. Woodland regeneration following recent major floods was tracked using onsite inspections over five years recording sapling growth and disappearance along with the breakage, bark removal and defoliation imposed by elephants, medium-sized browsing ruminants and porcupines. Fever trees were concentrated near the confluence of the two rivers where floodwaters inundated this region. Extreme floods carried away flanking ana trees while leaving sandy deposits open for recolonization. Elephants pushed over tall fever trees but not the ana trees, while regenerating saplings of both tree species were broken or uprooted. Browsing impalas defoliated juvenile trees contributing to their demise. These impacts contributed to the contraction or even disappearance of some fever tree groves and suppressed the growth and establishment of ana tree saplings. While these herbivores contributed to the shifting patch mosaic of these monospecific woodlands, the local distribution of these woodlands was associated with the soil features that they favoured.

The combined effects of dispersal and herbivores on stable states in coral reefs

The combined effects of dispersal and herbivores on stable states in coral reefs

20-year effects of white-tailed deer (Odocoileus virginianus) herbivory on vegetation composition and structure

Throughout the southeastern U.S., white-tailed deer (Odocoileus virginianus; hereafter deer) are the dominant herbivores and have the potential to impact vegetation communities through selective browse pressure. Previous studies regarding deer herbivory impacts focused on northeastern and midwestern U.S. forests. Additionally, most studies have observed herbivory effects over short timescales (i.e., <10 years). Therefore, we sought to determine deer herbivory effects on vegetation structure and composition among three different ecoregions in Mississippi at 0, 5, and ∼ 20 years after exclusion. In 2000, 3 pairs of experimental units were identified in each of the Upper Coastal Plain, Lower Coastal Plain, and Mississippi Alluvial Valley ecoregions. An exclosure treatment was randomly assigned within each pair (averaging 2.7 ha) with the other experimental unit a control. From May-June, vegetation structure and composition were measured among 10 systematic sampling points per plot during 2000, 2005, and 2021. While no treatment effects on vegetation composition and structure were observed, among-year differences suggested a shift in overstory canopy conditions between 2005 and 2021 towards greater basal area and canopy coverage resulting in a decrease in forbs, legumes, shade intolerant species, and high year-round deer-preferred forage species. Deer herbivory effects could have been obscured by overstory conditions, low deer densities, and similar baseline conditions reflecting past herbivory effects. Regional differences in forest structure and composition and exclosure breaches may also be responsible for the lack of treatment effects. Future studies should consider utilizing disturbance to offset prior herbivory impacts and to standardize overstory conditions.

The effects of dispersal, herbivory, and competition on plant community assembly.

Dispersal is a key process in community assembly but is often considered separately from downstream assembly processes (e.g., competition, herbivory). However, dispersal varies by species and can interact with other assembly processes through establishment as species enter communities. Here, we sought to distinguish the role of dispersal in community assembly and its interaction with two biotic assembly processes: competition and herbivory. We used a tallgrass prairie restoration experiment that manipulated the competitive and herbivore environments while allowing for natural dispersal and establishment from a diverse regional species pool into areas of low diversity. Dispersal, competition, and herbivory all influenced local communities. By tracking the spread of four target species across the plots, we found interspecific and intraspecific differences in establishment patterns, with herbivores influencing the number of individuals present and the distances species moved. At the community level, only dispersal and competition significantly influenced alpha diversity, but all three processes additively influenced community composition. There was also evidence of herbivore-competition and herbivore-colonization trade-offs in our experiment. Some species that could tolerate herbivory were less likely to establish in competitive environments, while others that could tolerate herbivory were more likely to disperse greater distances. More work is needed to understand the contexts under which dispersal variation affects community assembly and its synergy with other processes.

Undercover operation: Belowground insect herbivory modifies systemic plant defense and repels aboveground foraging insect herbivores

Plants attacked by insects may induce defenses locally in attacked plant tissues and/or systemically in non-attacked tissues, such as aboveground herbivory affecting belowground roots or belowground herbivory modifying aboveground tissues (i.e., cross-compartment systemic defense). Through induced systemic plant defenses, above-and belowground insect herbivores indirectly interact when feeding on a shared host plant. However, determining the systemic effects of herbivory on cross-compartment plant tissues and cascading consequences for herbivore communities remains underexplored. The goal of this study was to determine how belowground striped cucumber beetle (Acalymma vittatum) larval herbivory alters aboveground zucchini squash (Cucurbita pepo subsp. pepo) defenses and interactions with herbivores, including adult cucumber beetles and squash bugs (Anasa tristis). To explore this question, field and laboratory experiments were conducted to compare responses of aboveground herbivores to belowground larvae-damaged plants and non-damaged control plants. We also characterized changes in defensive chemicals and nutritional content of aboveground plant structures following belowground herbivory. We discovered belowground herbivory enhanced aboveground plant resistance and deterred aboveground foraging herbivores. We also found that larvae-damaged plants emitted higher amounts of a key volatile compound, (E)-β-ocimene, compared to non-damaged controls. Further investigation suggests that other mechanisms, such as plant nutrient content, may additionally contribute to aboveground herbivore foraging decisions. Collectively, our findings underscore connections between above-and belowground herbivore communities as mediated through induced systemic defenses of a shared host plant. Specifically, these findings indicate that belowground larval herbivory systemically enhances plant defenses and deters a suite of aboveground herbivores, suggesting larvae may manipulate aboveground plant defenses for their own benefit, while plants may benefit from enhanced systemic defenses against multi-herbivore attack.

Vegetation change on Mt. Teide, the Atlantic's highest volcano, inferred by incorporating the data underlying Humboldt'sTableau Physique des Iles Canaries

AbstractAimWe analyse the oldest available data on the high‐elevation vegetation on Tenerife's Mt. Teide, namely the species shown in A. von Humboldt's (1817)Tableau Physique des Iles Canaries(TPIC), which is based on his own 1799 visit and an 1815 visit by L. von Buch and C. Smith. The analysis is of interest in the context of climate change and biotic changes, such as the eradication of non‐native goats from the Teide National Park. Between 1944 and 2010, the summit region of Mt. Teide has warmed at a rate of 0.14°C/decade.LocationMt. Teide on Tenerife, Canary Islands.TaxonVascular plants.MethodsWe updated the taxonomy of the 197 species shown in the TPIC, data‐mined publications and letters, searched relevant herbaria for surviving collections, and compared historic and modern species presence, absence and elevational ranges.ResultsBoth Humboldt and Buch had to use formulas to convert barometer readings into elevations above sea level, and none of Humboldt's collections and few of Buch's are linked to precise elevations. The upper range limits of all 23 species for which we found data have shifted upward, with the average shift being 36.4 m per decade (1799/1815–2021). Four species that today are abundant were not recorded in 1815, suggesting population expansion, probably due to goat eradication.Main conclusionsWhile our data cannot disentangle the effects of climate change and changing herbivory, they provide the earliest available record on the vegetation on Mt. Teide and illustrate the magnitude of change.

CO2‐fertilisation enhances resilience to browsing in the recruitment phase of an encroaching savanna tree

Abstract CO2‐fertilisation is implicated in the widespread and significant woody encroachment of savannas due to CO2‐stimulated increases in below‐ground reserves that enhance sapling regrowth after fire. However, the effect of CO2 concentration ([CO2]) on tree responses to the other major disturbance in savannas, herbivory, is poorly understood. Herbivory responses cannot be predicted from fire responses, as herbivore effects occur earlier during establishment and are moderated by plant palatability and defence rather than below‐ground carbon accumulation. The relationship between herbivory and [CO2] is explored here using a widespread, strongly encroaching savanna tree, Vachellia karroo. Using greenhouse‐grown seedlings under past—through to predicted future—[CO2] (180–1000 ppm) and field‐grown seedlings under ambient [CO2], we assessed plant survival, growth, defence and palatability. Increasing [CO2] improves the tolerance of greenhouse‐grown seedlings to herbivory by stimulating growth and allowing a critical size threshold associated with survival to be reached earlier, thereby decreasing the probability of fatal herbivory during the vulnerable recruitment phase. Elevated [CO2] also decreases the time taken to reach a second size threshold linked to accelerated recovery of field‐grown seedlings following herbivory. Seedling growth responses to increasing [CO2] are nonlinear, suggesting that historic growth and survival enhancements are smaller than those predicted for the future. Increasing [CO2] is associated with greater resistance to herbivores (more branched shoot architecture) but not leaf palatability (C:N ratio) or defence (leaf tannins and spine density). Increasing V. karroo densities already constitute a major land management problem in southern African savannas. However, encroachment by this species, and likely other savanna tree species, may be greatly exacerbated under future [CO2], as tolerance to herbivory at the recruitment stage is further enhanced. Read the free Plain Language Summary for this article on the Journal blog.

Light competition drives herbivore and nutrient effects on plant diversity

Enrichment of nutrients and loss of herbivores are assumed to cause a loss of plant diversity in grassland ecosystems because they increase plant cover, which leads to a decrease of light in the understory1–3. Empirical tests of the role of competition for light in natural systems are based on indirect evidence, and have been a topic of debate for the last 40 years. Here we show that experimentally restoring light to understory plants in a natural grassland mitigates the loss of plant diversity that is caused by either nutrient enrichment or the absence of mammalian herbivores. The initial effect of light addition on restoring diversity under fertilization was transitory and outweighed by the greater effect of herbivory on light levels, indicating that herbivory is a major factor that controls diversity, partly through light. Our results provide direct experimental evidence, in a natural system, that competition for light is a key mechanism that contributes to the loss of biodiversity after cessation of mammalian herbivory. Our findings also show that the effects of herbivores can outpace the effects of fertilization on competition for light. Management practices that target maintaining grazing by native or domestic herbivores could therefore have applications in protecting biodiversity in grassland ecosystems, because they alleviate competition for light in the understory.

Wild herbivores enhance resistance to invasion by exotic cacti in an African savanna

Abstract Whether wild herbivores confer biotic resistance to invasion by exotic plants remains a key question in ecology. There is evidence that wild herbivores can impede invasion by exotic plants, but it is unclear whether and how this generalises across ecosystems with varying wild herbivore diversity and functional groups of plants, particularly over long‐term (decadal) time frames. Using data from three long‐term (13‐ to 26‐year) exclosure experiments in central Kenya, we tested the effects of wild herbivores on the density of exotic invasive cacti, Opuntia stricta and O. ficus‐indica (collectively, Opuntia), which are among the worst invasive species globally. We also examined relationships between wild herbivore richness and elephant occurrence probability with the probability of O. stricta presence at the landscape level (6150 km2). Opuntia densities were 74% to 99% lower in almost all plots accessible to wild herbivores compared to exclosure plots. Opuntia densities also increased more rapidly across time in plots excluding wild herbivores. These effects were largely driven by megaherbivores (≥1000 kg), particularly elephants. At the landscape level, modelled Opuntia stricta occurrence probability was negatively correlated with estimated species richness of wild herbivores and elephant occurrence probability. On average, O. stricta occurrence probability fell from ~0.56 to ~0.45 as wild herbivore richness increased from 6 to 10 species and fell from ~0.57 to ~0.40 as elephant occurrence probability increased from ~0.41 to ~0.84. These multi‐scale results suggest that any facilitative effects of Opuntia by wild herbivores (e.g. seed/vegetative dispersal) are overridden by suppression (e.g. consumption, uprooting, trampling). Synthesis. Our experimental and observational findings that wild herbivores confer resistance to invasion by exotic cacti add to evidence that conserving and restoring native herbivore assemblages (particularly megaherbivores) can increase community resistance to plant invasions.

Genotype, mycorrhizae, and herbivory interact to shape strawberry plant functional traits.

Arbuscular mycorrhizal fungi (AMF) and herbivores are ubiquitous biotic agents affecting plant fitness. While individual effects of pairwise interactions have been well-studied, less is known about how species interactions above and belowground interact to influence phenotypic plasticity in plant functional traits, especially phytochemicals. We hypothesized that mycorrhizae would mitigate negative herbivore effects by enhancing plant physiology and reproductive traits. Furthermore, we expected genotypic variation would influence functional trait responses to these biotic agents. To test these hypotheses, we conducted a manipulative field-based experiment with three strawberry (Fragaria x ananassa) genotypes to evaluate plant phenotypic plasticity in multiple functional traits. We used a fully-crossed factorial design in which plants from each genotype were exposed to mycorrhizal inoculation, herbivory, and the combined factors to examine effects on plant growth, reproduction, and floral volatile organic compounds (VOCs). Genotype and herbivory were key determinants of phenotypic variation, especially for plant physiology, biomass allocation, and floral volatiles. Mycorrhizal inoculation increased total leaf area, but only in plants that received no herbivory, and also enhanced flower and fruit numbers across genotypes and herbivory treatments. Total fruit biomass increased for one genotype, with up to 30-40% higher overall yield depending on herbivory. Herbivory altered floral volatile profiles and increased total terpenoid emissions. The effects of biotic treatments, however, were less important than the overall influence of genotype on floral volatile composition and emissions. This study demonstrates how genotypic variation affects plant phenotypic plasticity to herbivory and mycorrhizae, playing a key role in shaping physiological and phytochemical traits that directly and indirectly influence productivity.

Adverse effects of inbreeding on the transgenerational expression of herbivore-induced defense traits in Solanum carolinense.

In addition to directly inducing physical and chemical defenses, herbivory experienced by plants in one generation can influence the expression of defensive traits in offspring. Plant defense phenotypes can be compromised by inbreeding, and there is some evidence that such adverse effects can extend to the transgenerational expression of induced resistance. We explored how the inbreeding status of maternal Solanum carolinense plants influenced the transgenerational effects of herbivory on the defensive traits and herbivore resistance of offspring. Manduca sexta caterpillars were used to damage inbred and outbred S. carolinense maternal plants and cross pollinations were performed to produced seeds from herbivore-damaged and undamaged, inbred and outbred maternal plants. Seeds were grown in the greenhouse to assess offspring defense-related traits (i.e., leaf trichomes, internode spines, volatile organic compounds) and resistance to herbivores. We found that feeding by M. sexta caterpillars on maternal plants had a positive influence on trichome and spine production in offspring and that caterpillar development on offspring of herbivore-damaged maternal plants was delayed relative to that on offspring of undamaged plants. Offspring of inbred maternal plants had reduced spine production, compared to those of outbred maternal plants, and caterpillars performed better on the offspring of inbred plants. Both herbivory and inbreeding in the maternal generation altered volatile emissions of offspring. In general, maternal plant inbreeding dampened transgenerational effects of herbivory on offspring defensive traits and herbivore resistance. Taken together, this study demonstrates that inducible defenses in S. carolinense can persist across generations and that inbreeding compromises transgenerational resistance in S. carolinense.

Herbivory modifies plant symbiont number and impact on host plant performance in the field.

Species interactions are a unifying theme in ecology and evolution. Both fields are currently moving beyond their historical focus on isolated pairwise relationships to understand how ecological communities affect focal interactions. Additional species can modify both the number of interactions and the fitness consequences of each interaction (i.e., selection). Although only selection affects the evolution of the focal interaction, the two are often conflated, limiting our understanding of the evolution of multispecies interactions. We manipulated aboveground herbivory on the legume Medicago lupulina in the field and quantified its effect on number of symbionts and the per-symbiont impact on plant performance in two belowground symbioses: mutualistic rhizobia bacteria (Ensifer meliloti) and parasitic root-knot nematodes (Meloidogyne hapla). We found that herbivores modified the number of rhizobia nodules, as well as the benefit per nodule. However, each effect was specific to a distinct herbivory regime: natural herbivory affected nodule number, whereas leafhoppers (Cicadellidae) weakened the per nodule benefit. We did not detect any effect of herbivory on nematode gall number or the cost of infection. Our data demonstrate that distinguishing between symbiont number from the fitness consequences of symbiosis is crucial to accurately infer how pairwise interactions will evolve in a community.