Unraveling the multiple facilitative effects of consumers on marine primary producers.

The loss of consumers threatens the integrity of ecological systems, but the mechanisms underlying the effects on communities and ecosystems remain difficult to predict. This is, in part, due to the complex roles that consumers play in those systems. Here, we highlight this complexity by quantifying two mechanisms by which molluscan grazers-typically thought of as consumers of their algal resources-facilitate algae on rocky shores. Initial observations in high-zone tide pools revealed that both water-column ammonium concentrations and photosynthetic biomass were higher in pools containing higher densities of grazers, suggesting that local-scale nutrient recycling by the grazers could be enhancing algal biomass. We assessed this possibility by experimentally manipulating grazer abundances at the level of whole tide pools but controlling access of those grazers to experimental plots within each pool. Contrary to predictions that algal biomass inside grazer exclusions would increase as grazer abundances in the pools increased, we found that algal biomass inside grazer-exclusion fences was unaffected by grazer abundances. Instead, the consumptive effects of grazers that were evident at low grazer abundances transitioned to facilitative effects as experimentally manipulated grazer abundances increased. This finding suggested that these positive interactions were associated with the physical presence of grazers and not just grazers' effects on nutrient availability. Subsequent experiments highlighted the potential role of "slime"-the pedal mucous trails left behind as the mollusks crawl on the substratum-in promoting the recruitment of algae and thereby mediating a spatial subsidy of new organic matter into the system. Furthermore, different grazer groups contributed disproportionately to ammonium excretion (i.e., turban snails) versus slime production (i.e., littorine snails), suggesting a potential role for grazer diversity. Our work highlights the complex ways in which consumers affect their resources, including multiple, complementary mechanisms by which these grazers facilitate the algae they consume.

Functional characterization of a novel terpene synthase GaTPS1 involved in (E)-α-bergamotene biosynthesis in Gossypium arboreum.

Terpenoids in plants are mainly synthesized by terpene synthases (TPSs), which play an important role in plant-environment interactions. Gossypium arboreum is one of the important cotton cultivars with excellent pest resistance, however, the biosynthesis of most terpenoids in this plant remains unknown. In this study, we performed a comparative transcriptome analysis of leaves from intact and Helicoverpa armigera-infested cotton plants. The results showed that the H. armigera infestation mainly induced the JA signaling pathway, ten TPS genes were differentially expressed in G. arboreum leaves. Among them, a novel terpene synthase, GaTPS1, was heterologously expressed and functionally characterized in vitro. The enzymatic reaction indicated that recombinant GaTPS1 was primarily responsible for the production of (E)-α-bergamotene. Moreover, molecular docking and site-directed mutagenesis analysis demonstrated that two amino acid residues, A412L and Y535F, distinctly influenced the catalytic activities and product specificity of GaTPS1. The mutants GaTPS1-A412L and GaTPS1-Y535F resulted in a decrease in the proportion of products (E)-α-bergamotene and D-limonene, while an increase in the proportion of products (E)-ß-farnesene, α-pinene and ß-myrcene. Our findings provide valuable insights into understanding the molecular basis of terpenoid diversity in G. arboreum, with potential applications in plant metabolism regulation and the improvement of resistant cotton cultivars.

Direct and indirect effects of copepod grazers on community structure.

Ecological theory and empirical research show that both direct lethal effects and indirect non-lethal effects can structure the composition of communities. While the direct effects of grazers on marine phytoplankton communities are well studied, their indirect effects are still poorly understood. Direct and indirect effects are inherently difficult to disentangle in plankton food webs. In this study we evaluate the indirect effects of copepod grazers on community function and structure using isolated chemical alarm signals, copepodamides. We expose intact summer and spring communities to direct grazing from copepods, or to chemical alarm cues without the presence of grazers in controlled experiments. The effects of direct grazing on ecosystem function were moderate in both experiments as indicated by levels of chlorophyll and primary production. Indirect and direct effects resulted in changes in the composition of both the eukaryote and prokaryote communities as shown by metabarcoding of 18S and 16S rRNA. Size structure analysis suggests that direct grazing and copepodamide exposure both favoured smaller organisms (< 10-15 µm) corroborating the size-structuring effect of copepod grazers. We conclude that the well-established effect of copepods on phytoplankton communities results from a combination of direct and indirect effects. This is a first attempt to isolate indirect effects of copepods on community structure and the results suggest that a full mechanistic understanding of the structuring effect of copepods will require insights to both direct and indirect effects of consumers as demonstrated for other ecosystems components.

Entomopathogenic Nematodes-Killed Insect Cadavers in the Rhizosphere Activate Plant Direct and Indirect Defences Aboveground.

Plants can perceive and respond to external stimuli by activating both direct and indirect defences against herbivores. Soil-dwelling entomopathogenic nematodes (EPNs), natural enemies of root-feeding herbivores, carry symbiotic bacteria that grow and reproduce once inside arthropod hosts. We hypothesized that the metabolites produced by EPN-infected insect cadavers could be perceived by plants, thereby activating plant defences systemically. We tested this hypothesis by adding three EPN-infected Galleria mellonella cadavers to maize plants and testing plant responses against a major maize pest (Spodoptera frugiperda) and one of its parasitoids (Trichogramma dendrolimi). We found that S. frugiperda females deposited fewer, and caterpillars fed less on maize plants growing near EPN-infected cadavers than on control plants. Accordingly, EPN-infected cadavers triggered the systemic accumulation of defence hormones (SA), genes (PR1), and enzymes (SOD, POD, and CAT) in maize leaves. Furthermore, four volatile organic compounds produced by plants exposed to EPN-infected cadavers deterred S. frugiperda caterpillars and female adults. However, these compounds were more attractive to T. dendrolimi parasitoids. Our study enhances the understanding of the intricate relationships within the above- and belowground ecosystems and provides crucial insights for advancing sustainable pest management strategies.

Foraging tunnel disturbances created by small subterranean herbivores enhance soil organic carbon stability but reduce carbon sequestration in different alpine grassland types.

Foraging tunnel disturbances by small subterranean herbivores can alter soil properties and nutrient dynamics in grasslands, potentially altering soil organic carbon (SOC). Examining the impact of foraging tunnel disturbances on mineral-associated organic carbon (MAOC) and particulate organic carbon (POC) is crucial for understanding SOC changes and its stability. However, the effects of these disturbances on POC and MAOC are not well documented. This study uses the plateau zokor (Eospalax baileyi) as a focal subterranean herbivore to investigate the effects of foraging tunnel disturbances on POC and MAOC in alpine steppes, alpine meadows, and alpine meadow steppes. Ninety paired quadrats were used for soil and plant sampling across three alpine grassland types. Results show that foraging tunnel disturbances consistently reduced POC concentrations across all grassland types, with reductions of 44.01 % in alpine steppes, 20.86 % in alpine meadows, and 29.58 % in alpine meadow steppes. MAOC concentrations decreased by 16.49 % in alpine steppes, while no significant changes in MAOC were observed in alpine meadows and alpine meadow steppes. The reduction in the POC to MAOC ratio indicates increased SOC stability. However, despite this increased stability, the change may lead to a decrease in overall carbon sequestration potential, as the total SOC in the soil declines. The main factors influencing POC and MAOC were soil moisture, belowground biomass, and microbial biomass carbon, with their influences varying by grassland type. The findings demonstrate that foraging tunnel disturbances by plateau zokors can lead to substantial modifications in SOC composition, influencing both its stability and sequestration potential. The disturbances necessitate tailored management strategies to mitigate their impacts, considering the unique characteristics of each grassland type to preserve carbon sequestration potential. This study contributes to a deeper understanding of the ecological role of small subterranean herbivores in the carbon cycle of alpine grassland ecosystems.

Field evidence for the role of plant volatiles induced by caterpillar oral secretion in prey localization by predatory social wasps.

One assumed function of herbivore-induced plant volatiles (HIPVs) is to attract natural enemies of the inducing herbivores. Field evidence for this is scarce. In addition, the assumption that elicitors in oral secretions that trigger the volatile emissions are essential for the attraction of natural enemies has not yet been demonstrated under field conditions. After observing predatory social wasps removing caterpillars from maize plants, we hypothesized that these wasps use HIPVs to locate their prey. To test this, we conducted an experiment that simultaneously explored the importance of caterpillar oral secretions in the interaction. Spodoptera caterpillars pinned onto mechanically damaged plants treated with oral secretion were more likely to be attacked by wasps compared with caterpillars on plants that were only mechanically wounded. Both of the latter treatments were considerably more attractive than plants only treated with oral secretion or left untreated. Subsequent analyses of headspace volatiles confirmed differences in emitted volatiles that likely account for the differential predation across treatments. These findings highlight the importance of HIPVs in prey localization by social wasps, hitherto underappreciated potential biocontrol agents and provide evidence for the role that elicitors play in inducing attractive odour blends.

Arbuscular mycorrhizal fungi influence belowground interactions between a specialist root-feeder and its natural enemy.

As primary producers, plants play a central role in mediating interactions across trophic levels. Although plants are the primary food source for herbivorous insects, they can protect themselves from herbivore damage. Many plants produce toxic compounds that directly reduce herbivore feeding, but plants also protect themselves indirectly by attracting natural enemies of the attacking herbivore through volatile signaling. These so-called tri-trophic interactions have historically been documented aboveground in aerial plant parts but are also known to occur belowground in root systems. In addition to herbivores, plants directly interact with other organisms, which can influence the outcomes of tri-trophic interactions. Arbuscular mycorrhizal fungi (AMF) are symbiotic soil microbes that colonize the roots of plants and facilitate nutrient uptake. These microbes can alter plant chemistry and subsequent resistance to herbivores. Few studies, however, have shown how AMF affect tri-trophic interactions above- or belowground. This study examines how AMF colonization affects the emission of root volatiles when plants are under attack by western corn rootworm, a problematic pest of corn, and subsequent attraction of entomopathogenic nematodes, a natural enemy of western corn rootworm. Mycorrhizal fungi increased rootworm survival but decreased larval weight. Differences were detected across root volatile profiles, but there was not a clear link between volatile signaling and nematode behavior. Nematodes were more attracted to non-mycorrhizal plants without rootworms and AMF alone in soil, suggesting that AMF may interfere with cues that are used in combination with volatiles which nematodes use to locate prey.

Relationships between abiotic factors, foliage chemistry and herbivory in a tropical montane ecosystem.

Herbivore-plant interactions are fundamental processes shaping ecosystems, yet their study is challenged by their complex connections within broader ecosystem processes, requiring a nuanced understanding of ecosystem dynamics. This study investigated the relationship between nutrient availability and insect herbivory in the Australian Wet Tropics. Our objectives were threefold. Firstly, to understand what factors influence nutrient availability for plants and herbivores across the landscape; secondly, to investigate how trees of different species respond to nutrient availability; and thirdly, to unravel how the relationships between resources and plant chemistry affect herbivory. We established a network of 25 study sites covering important abiotic gradients, including temperature, precipitation, and geology. Employing a hierarchical modelling approach, we assessed the influence of climate and geology on resource availability for plants, primarily in the form of soil nutrients. Then, we explored the influence of the above factors on the interaction between herbivory and foliage chemistry across three widespread rainforest tree species, comparing how these relationships emerged across genera. Our findings suggest an overarching influence of climate and geology over soil chemistry, foliar nitrogen, and insect herbivory, both directly and indirectly. However, individual constituents of soil fertility showed equivocal influences on spatial patterns of foliage chemistry once site geological origin was accounted for, suggesting a questionable relationship between individual soil nutrients and foliar composition. We have demonstrated that herbivore-plant interactions are complex dynamics regulated by an intricate web of relationships spanning different biogeochemical processes. While our results provide some support to the notion that herbivory is affected by resource availability, different species growing under the same conditions can show differing responses to the same resources, highlighting the importance of identifying specific limiting factors rather than simpler proxies of resource availability.

Historical invasion rates vary among insect trophic groups.

Globalization has spread thousands of invasive insect species into new world regions,1,2,3 causing severe losses in ecosystem services. Previous work proposed that plant invasions facilitate insect invasions through the creation of niches for non-native herbivores.3,4,5,6 Despite the impact of insect invasions, a comprehensive understanding is lacking on how invasion success varies among insect feeding groups. We therefore compiled the predominant larval trophic groups (herbivores, predators, parasites, detritivores, and brood-carers) for 5,839 non-native insect species in nine world regions to compare (1) proportions of species in each group between non-native species and the world's fauna, (2) how invasion success for each trophic group has changed over the last three centuries, and (3) how historical herbivore invasions are related to plant invasions over time and parasite invasions are related to herbivores. We find that herbivores represent a significantly larger proportion (52.4%) among non-native insects compared with the world fauna (38.4%), whereas proportions of non-native detritivores (including fungivores), predators, and brood-carers are significantly lower; parasite proportions do not significantly differ. Predators and detritivores dominated among invasions in the 18th century but subsequently diminished, likely due to changing invasion pathways, whereas proportions of herbivores, parasites, and brood-carers increased over time. We found herbivore invasions to lag 80 years behind plant invasions, whereas parasitoids appear to co-invade with their herbivore hosts. The dominance of herbivores among non-native insects and their strong cross-correlation with plant invasions further strengthens the hypothesis that plant invasions drive the global rise in numbers of non-native insects.

Defense Molecules of the Invasive Plant Species Ageratum conyzoides.

Ageratum conyzoides L. is native to Tropical America, and it has naturalized in many other tropical, subtropical, and temperate countries in South America, Central and Southern Africa, South and East Asia, Eastern Austria, and Europe. The population of the species has increased dramatically as an invasive alien species, and it causes significant problems in agriculture and natural ecosystems. The life history traits of Ageratum conyzoides, such as its short life cycle, early reproductive maturity, prolific seed production, and high adaptive ability to various environmental conditions, may contribute to its naturalization and increasing population. Possible evidence of the molecules involved in the defense of Ageratum conyzoides against its natural enemies, such as herbivore insects and fungal pathogens, and the allelochemicals involved in its competitive ability against neighboring plant species has been accumulated in the literature. The volatiles, essential oils, extracts, residues, and/or rhizosphere soil of Ageratum conyzoides show insecticidal, fungicidal, nematocidal, and allelopathic activity. The pyrrolizidine alkaloids lycopsamine and echinatine, found in the species, are highly toxic and show insecticidal activity. Benzopyran derivatives precocenes I and II show inhibitory activity against insect juvenile hormone biosynthesis and trichothecene mycotoxin biosynthesis. A mixture of volatiles emitted from Ageratum conyzoides, such as ß-caryophyllene, ß-bisabolene, and ß-farnesene, may work as herbivore-induced plant volatiles, which are involved in the indirect defense function against herbivore insects. Flavonoids, such as nobiletin, eupalestin, 5'-methoxynobiletin, 5,6,7,3',4',5'-hexamethoxyflavone, and 5,6,8,3,4',5'-hexamethoxyflavone, show inhibitory activity against the spore germination of pathogenic fungi. The benzoic acid and cinnamic acid derivatives found in the species, such as protocatechuic acid, gallic acid, p-coumaric acid, p-hydroxybenzoic acid, and ferulic acid, may act as allelopathic agents, causing the germination and growth inhibition of competitive plant species. These molecules produced by Ageratum conyzoides may act as defense molecules against its natural enemies and as allelochemicals against neighboring plant species, and they may contribute to the naturalization of the increasing population of Ageratum conyzoides in new habitats as an invasive plant species. This article presents the first review focusing on the defense function and allelopathy of Ageratum conyzoides.

Mathematical modeling predicts that endemics by generalist insects are eradicated if nearly all plants produce constitutive defense.

Plants with constitutive defense chemicals exist widely in nature. The phenomenon is backed by abundant data from plant chemical ecology. Sufficient data are also available to conclude that plant defenses act as deterrent and repellent to attacking herbivores, particularly deleterious generalist insects. In the wild, generalist species are usually not endemic, meaning they are not restricted to certain plant species in a region. Therefore, our objective is to inspect theoretically whether evolution of chemical defenses in all plant species eradicate an endemic by any generalist species. The objective is addressed by developing deterministic ordinary differential equations under the following conditions: Plants without constitutive defenses are susceptible to oviposition by generalist insects, while they become defended against generalists by storing chemical defenses. From the models, we explicitly obtain that a generalist-free stable state is only possible if the vast majority of all plant individuals have chemical defenses. The model also allows one to predict the highest possible percentage of undefended plant individuals, which may be considered as free-riders.

Comprehensive systematic review and meta-analysis of microplastic prevalence and abundance in freshwater fish species: the effect of fish species habitat, feeding behavior, and Fulton's condition factor.

Microplastics are emerging pollutants that cause health problems for aquatic organisms. Fish is one of the important organisms because of its consumption by humankind. The present study examines the abundance and prevalence of microplastics in freshwater fish species through a systematic review study while considering five important factors, i.e. water resources, habitat, feeding behavior, Fulton's condition factor, and microplastic characteristics. A comprehensive meta-analysis was undertaken to evaluate relevant publications in terms of microplastic abundance. Articles published up to July 30, 2022 were found through Global search engines including, Web of Science, Scopus, and PubMed. In total, 786 articles were found that 53 and 42 articles were used for qualitative review and meta-analysis, respectively. This was carried out by a random-effects model with high heterogeneity (I2 = 99.76%). According to the data, the highest attention in microplastic research in body part and water sources are related to gastrointestinal tract (n = 259 (~ 80%)) and rivers (n = 189 (~ 58%)), respectively. According to the results, the average microplastic prevalence range was 5 -100%, and microplastic abundance was within the 0.04-204 items range per individual. The difference between microplastic prevalence and abundance for the key factors for parametric and nonparametric data were analyzed using Analysis of variance (ANOVA) and the Kruskal-Wallis test, respectively. According to the Baujat plot, two studies (ID: 27 and 25) revealed the minimal influence of microplastics abundance. Conclusively, the average microplastics abundance according to the pooled data, varied between 2.23 and 2.48, with a mean of 2.35 items per individual in the studies overall. It is concluded that the amount of ingested microplastics by fish is related only to physiology (height, weight, and body structure) but not feeding behavior, habitat, and surrounding water. Supplementary Information: The online version contains supplementary material available at 10.1007/s40201-024-00907-z.

Cover crop rotation suppresses root-knot nematode infection by shaping soil microbiota.

Cover crop integration into grain crop rotations is a promising strategy for mitigating nematode-induced diseases in agriculture. However, the precise mechanisms underlying this phenomenon remain elusive. Here, we first assessed the impact of five commonly used cover crops on the suppression of rice root-knot nematodes (RKNs). We then chose ryegrass as a model to explore the mechanistic basis of the suppression effect. Contrary to expectations, while ryegrass rotation significantly enhances soil fertility, this increased fertility has minimal impact on RKN suppression. Furthermore, neither integrated ryegrass residues nor root exudates exhibit direct toxicity towards RKNs. We demonstrated that ryegrass rotation primarily suppresses RKNs by enriching beneficial soil microbiota. By complementing with isolated bacteria strains, we further demonstrated that ryegrass-enriched bacteria not only directly reduce RKN infectivity and preference, but also activate plant immunity via the OsLRR-RLK-MAPK-WRKY-JA cascade, thereby diminishing RKN infection. Our study highlights the crucial role of soil microbiota in plant-nematode interactions, challenging conventional views on the direct effects of cover crops in nematode suppression. It offers a mechanistic understanding of the regulation potential and action modes of cover crops in mitigating nematode diseases, providing valuable insights for sustainable agriculture.

Identification of Linalool Disaccharide Glycoside (Linalyl ß-Vicianoside) in Soybean Leaves and Its Implication for Herbivore Resistance.

Linalool is anticipated to have significant ecological roles. In this study, linalyl 6-O-α-arabinopyranosyl-ß-D-glucopyranoside (linalyl ß-vicianoside: LinVic) was synthesized, and a linalool diglycoside purified from soybean leaves was identified as LinVic by using liquid chromatography-mass spectrometry. High levels of LinVic were detected in leaves and sepals during soybean plant growth. The LinVic content did not significantly increase following methyl jasmonate treatment of the leaves, indicating that its synthesis is independent of the jasmonic acid signaling pathway. In addition to LinVic, soybean also contains 1-octen-3-yl primeveroside. We treated soybean leaves with vaporized linalool and 1-octen-3-ol to determine whether the glycosylation system discriminates between these two volatile alcohols. Linalool treatment resulted in the accumulation of LinVic, while 1-octen-3-ol treatment caused little change in the amount of 1-octen-3-yl primeveroside, suggesting discrimination between these compounds. Linalool-treated soybean leaves exhibited increased resistance against common cutworms, indicating that LinVic may contribute to herbivore resistance.

Combined Effects of Heavy Metal and Simulated Herbivory on Leaf Trichome Density in Sunflowers.

Trichomes play a key role in both heavy metal tolerance and herbivory defense, and both stressors have been shown to induce increased trichome density. However, the combined effect of these stressors on trichome density in general, and specifically on metal-hyperaccumulating plants, has yet to be examined. The aim of this study was to test the effect of cadmium availability and herbivory on leaf trichome density and herbivore deterrence in the metal hyperaccumulator Helianthus annuus. To test this, H. Annuus plants were grown in control pots or pots inoculated with 10 mg/kg cadmium and were subjected to either no herbivory or simulated herbivory using mechanical damage and foliar jasmonic acid application. Herbivore deterrence was tested in a feeding assay using Spodoptera littoralis caterpillars. Interestingly, while the trichome density of H. annuus increased by 79% or 53.5% under high cadmium availability or simulated herbivory, respectively, it decreased by 26% when the stressors were combined. Furthermore, regardless of cadmium availability, simulated herbivory induced a 40% increase in deterrence of S. littoralis. These findings suggest that the combination of metal availability and herbivory might present excessive stress to hyperaccumulators. Moreover, they suggest that the risk of metal bioaccumulation in phytoremediation can be reduced by simulated herbivory.

Climate change and deer in boreal and temperate regions: From physiology to population dynamics and species distributions.

Climate change causes far-reaching disruption in nature, where tolerance thresholds already have been exceeded for some plants and animals. In the short term, deer may respond to climate through individual physiological and behavioral responses. Over time, individual responses can aggregate to the population level and ultimately lead to evolutionary adaptations. We systematically reviewed the literature (published 2000-2022) to summarize the effect of temperature, rainfall, snow, combined measures (e.g., the North Atlantic Oscillation), and extreme events, on deer species inhabiting boreal and temperate forests in terms of their physiology, spatial use, and population dynamics. We targeted deer species that inhabit relevant biomes in North America, Europe, and Asia: moose, roe deer, wapiti, red deer, sika deer, fallow deer, white-tailed deer, mule deer, caribou, and reindeer. Our review (218 papers) shows that many deer populations will likely benefit in part from warmer winters, but hotter and drier summers may exceed their physiological tolerances. We found support for deer expressing both morphological, physiological, and behavioral plasticity in response to climate variability. For example, some deer species can limit the effects of harsh weather conditions by modifying habitat use and daily activity patterns, while the physiological responses of female deer can lead to long-lasting effects on population dynamics. We identified 20 patterns, among which some illustrate antagonistic pathways, suggesting that detrimental effects will cancel out some of the benefits of climate change. Our findings highlight the influence of local variables (e.g., population density and predation) on how deer will respond to climatic conditions. We identified several knowledge gaps, such as studies regarding the potential impact on these animals of extreme weather events, snow type, and wetter autumns. The patterns we have identified in this literature review should help managers understand how populations of deer may be affected by regionally projected futures regarding temperature, rainfall, and snow.

Herbivore and native plant diversity synergistically resist alien plant invasion regardless of nutrient conditions.

Alien plant invasion success can be inhibited by two key biotic factors: native herbivores and plant diversity. However, few studies have experimentally tested whether these factors interact to synergistically resist invasion success, especially factoring in changing global environments (e.g. nutrient enrichment). Here we tested how the synergy between native herbivores and plant diversity affects alien plant invasion success in various nutrient conditions. For this purpose, we exposed alien plant species in pot-mesocosms to different levels of native plant diversity (4 vs. 8 species), native generalist herbivores, and high and low soil nutrient levels. We found that generalist herbivores preferred alien plants to native plants, inhibiting invasion success in a native community. This inhibition was amplified by highly diverse native communities. Further, the amplified effect between herbivory and native plant diversity was independent of nutrient conditions. Our results suggest that a higher diversity of native communities can strengthen the resistance of native generalist herbivores to alien plant invasions by enhancing herbivory tolerance. The synergistic effect remains in force in nutrient-enriched habitats that are always invaded by alien plant species. Our results shed light on the effective control of plant invasions using multi-trophic means, even in the face of future global changes.

How does plant chemodiversity evolve? Testing five hypotheses in one population genetic model.

Plant chemodiversity, the diversity of plant-specialized metabolites, is an important dimension of biodiversity. However, there are so far few mathematical models to test verbal hypotheses on how chemodiversity evolved. Here, we develop such a model to test predictions of five hypotheses: the 'fluctuating selection hypothesis', the 'dominance reversal hypothesis', the interaction diversity hypothesis, the synergy hypothesis, and the screening hypothesis. We build a population genetic model of a plant population attacked by herbivore species whose occurrence fluctuates over time. We study the model using mathematical analysis and individual-based simulations. As predicted by the 'dominance reversal hypothesis', chemodiversity can be maintained if alleles conferring a defense metabolite are dominant with respect to the benefits, but recessive with respect to costs. However, even smaller changes in dominance can maintain polymorphism. Moreover, our results underpin and elaborate predictions of the synergy and interaction diversity hypotheses, and, to the extent that our model can address it, the screening hypotheses. By contrast, we found only partial support for the 'fluctuating selection hypothesis'. In summary, we have developed a flexible model and tested various verbal models for the evolution of chemodiversity. Next, more mechanistic models are needed that explicitly consider the organization of metabolic pathways.

A conserved protein family in mirid bug Riptortus pedestris plays dual roles in regulating plant immunity.

The mirid bug (Riptortus pedestris), a major soybean pest, migrates into soybean fields during the pod filling stage and causes staygreen syndrome, which leads to substantial yield losses. The mechanism by which R. pedestris elicits soybean (Glycine max) defenses and counter-defenses remains largely unexplored. In this study, we characterized a protein family from R. pedestris, designated Riptortus pedestris HAMP 1 (RPH1) and its putative paralogs (RPH1L1, 2, 3, 4, and 5), whose members exhibit dual roles in triggering and inhibiting plant immunity. RPH1 and RPH1L1 function as herbivore-associated molecular patterns (HAMPs), activating pattern-triggered immunity (PTI) in tobacco (Nicotiana benthamiana) and G. max. Furthermore, RPH1 stimulates jasmonic acid and ethylene biosynthesis in G. max, thereby enhancing its resistance to R. pedestris feeding. Additionally, RPH1 homologs are universally conserved across various herbivorous species, with many homologs also acting as HAMPs that trigger plant immunity. Interestingly, the remaining RPH1 putative paralogs (RPH1L2-5) serve as effectors that counteract RPH1-induced PTI, likely by disrupting the extracellular perception of RPH1. This research uncovers a HAMP whose homologs are conserved in both chewing and piercing-sucking insects. Moreover, it unveils an extracellular evasion mechanism utilized by herbivores to circumvent plant immunity using functionally differentiated paralogs.

Insights into the evolution of herbivory from a leaf-mining fly.

Herbivorous insects and their host plants comprise most known species on Earth. Illuminating how herbivory repeatedly evolved in insects from non-herbivorous lineages is critical to understanding how this biodiversity is created and maintained. We characterized the trophic niche of Scaptomyza flava, a representative of a lineage nested within the Drosophila that transitioned to herbivory ~10-15 million years ago. We used natural history studies to determine if S. flava is a true herbivore or a cryptic microbe-feeder, given that the ancestral character state for the family Drosophilidae is likely microbe-feeding. Specifically, we quantified oviposition substrate choice and larval viability across food-types, trophic-related morphological traits, and nitrogen isotope and sterol profiles across putatively herbivorous and non-herbivorous drosophilids. The results of these studies show that S. flava is an obligate herbivore of living plants. Paired with its genetic model host, Arabidopsis thaliana, S. flava is a novel and powerful system for exploring mechanisms underlying the evolution of herbivory, a complex trait that enabled the exceptional diversification of insects.