植食者取食诱导植物产生互益素的研究

传统上仅在两级营养水平上研究植物对植食者的防御。也就是说,仅在天敌与植食者或植食者与植物水平上进行研究。但是,进一步的研究越来越清楚地显示植物可以直接影响天敌植食者。研究表明,植食者诱导的植物信号物质可以诱集天敌消灭害虫,当植物被放在这种相互联系中考...     

Host Feeding by an Herbivore Improves the Performance of Offspring

Herbivores have developed diverse strategies to manipulate host plants for their own benefits. The gall induction by the maize orange leafhopper Cicadulina bipunctata is different from that by other gall-inducing insects in that the galls are induced not on feeding sites but appear on distant, newly developing leaves. In addition, adult C. bipunctata are highly mobile and seldom feed on gall tissue that they have induced. These mean that the gall induction by C. bipunctata is unlikely to contribute to the fitness of the inducer itself. The objective of this study was to determine whether manipulation of the host plant by this leafhopper has a subsequent benefit to offspring. Adults feeding on maize seedlings caused a partial change in the glucose content and a remarkable change in the accumulation of free amino acids in the gall tissue. Increases in emergence and developmental rates were observed in nymphs feeding on gall tissue induced by prior adult feeding. Such improvements were not evident in nymphs feeding on a C. bipunctata-resistant variety, which rarely displays galls after C. bipunctata feeding, nor on maize seedlings previously foraged by another leafhopper, Psammotettix striatus. The results indicate that gall tissue induced by adult C. bipunctata contribute to better performance of its offspring through improvement of the nutritional components of host plants.     

Predicting Habitat Utilization and Extent of Ecosystem Disturbance by an Increasing Herbivore Population

Herbivory can lead to shifts in ecosystem state or changes in ecosystem functioning, and recovery from herbivory is particularly slow in disturbance-sensitive ecosystems such as arctic tundra. Herbivore impacts on ecosystems are variable in space and time due to population fluctuations and selective utilization of habitats; thus there is a need to accurately predict herbivore impacts at the landscape scale. The habitat utilization and extent of disturbance caused by increasing populations of pink-footed geese (Anser brachyrhynchus) foraging in the high arctic tundra of Svalbard were assessed using a predictive model of the population’s habitat use. Pink-footed geese arrive in Svalbard in early spring when they forage for belowground plant parts; this foraging (called grubbing) can cause vegetation loss and soil disturbance. Surveys of the extent and intensity of grubbing were carried out to develop predictive models that were subsequently tested against data collected during the following year from different areas. Both habitat type at a particular point and the amount of preferred fen habitat in the surrounding area were powerful predictors of grubbing likelihood and the developed model correctly classified over 69% of validation observations with an AUC of 0.75. Pink-footed geese showed a strong preference for wetter habitats within low-lying landscapes. Extrapolation of the predictive model across the archipelago showed that a maximum potential area of 2300 km² (3.8% of the archipelago) could be disturbed by grubbing. Thus, increasing populations of geese may cause large-scale vegetation loss and soil disturbance in arctic ecosystems.     

Influence of Global Atmospheric Change on the Feeding Behavior and Growth Performance of a Mammalian Herbivore,Microtus ochrogaster

Global atmospheric change is influencing the quality of plants as a resource for herbivores. We investigated the impacts of elevated carbon dioxide (CO₂) and ozone (O₃) on the phytochemistry of two forbs, Solidago canadensis and Taraxacum officinale, and the subsequent feeding behavior and growth performance of weanling prairie voles (Microtus ochrogaster) feeding on those plants. Plants for the chemical analyses and feeding trials were harvested from the understory of control (ambient air), elevated CO₂ (560 µl CO₂ l⁻¹), and elevated O₃ (ambient × 1.5) rings at the Aspen FACE (Free Air CO₂ Enrichment) site near Rhinelander, Wisconsin. We assigned individual voles to receive plants from only one FACE ring and recorded plant consumption and weanling body mass for seven days. Elevated CO₂ and O₃ altered the foliar chemistry of both forbs, but only female weanling voles on the O₃ diet showed negative responses to these changes. Elevated CO₂ increased the fiber fractions of both plant species, whereas O₃ fumigation elicited strong responses among many phytochemical components, most notably increasing the carbon-to-nitrogen ratio by 40% and decreasing N by 26%. Consumption did not differ between plant species or among fumigation treatments. Male voles were unaffected by the fumigation treatments, whereas female voles grew 36% less than controls when fed O₃-grown plants. These results demonstrate that global atmospheric change has the potential to affect the performance of a mammalian herbivore through changes in plant chemistry.     

Herbivore release through cascading risk effects

Predators influence prey through consumption, and through trait-mediated effects such as emigration in response to predation risk (risk effects). We studied top-down effects of (sub-) adult wolf spiders (Lycosidae) on arthropods in a meadow. We compared risk effects with the overall top-down effect (including consumption) by gluing the chelicers of wolf spiders to prevent them from killing the prey. In a field experiment, we created three treatments that included either: (i) intact (‘predation’) wolf spiders; (ii) wolf spiders with glued chelicers (‘risk spiders’); or (iii) no (sub-) adult wolf spiders. Young wolf spiders were reduced by their (sub-) adult congeners. Densities of sheetweb spiders (Linyphiidae), a known intraguild prey of wolf spiders, were equally reduced by the presence of risk and predation wolf spiders. Plant- and leafhoppers (Auchenorrhyncha) showed the inverse pattern of higher densities in the presence of both risk and predation wolf spiders. We conclude that (sub-) adult wolf spiders acted as top predators, which reduced densities of intermediate predators and thereby enhanced herbivores. Complementary to earlier studies that found trait-mediated herbivore suppression, our results demonstrate that herbivores can be enhanced through cascading risk effects by top predators.     

Decreased Response to Feeding Deterrents Following Prolonged Exposure in the Larvae of a Generalist Herbivore, Trichoplusia ni (Lepidoptera: Noctuidae)

We investigated the role of experience with several antifeedants on the feeding behavior of a generalist herbivore, Trichoplusia ni. Second-, third-, and fifth-instar larvae of T. ni were examined for their feeding responses to plant extracts (Melia volkensii, Origanum vulgare) and individual plant allelochemicals (cymarin, digitoxin, xanthotoxin, toosendanin, and thymol), after being exposed to them continually beginning as neonates. All tested instars of T. ni were capable of showing a decreased antifeedant response following prolonged exposure to most of the antifeedants tested compared with their naive conspecifics. Cardenolides (digitoxin and cymarin) were the exceptions. The response to oregano was affected as a result of previous exposure to different concentrations of oregano, unlike M. volkensii, leading us to conclude that T. ni sensitivity varies between stimuli and cannot be generalized. To demonstrate that decreased deterrence following prolonged exposure to M. volkensii was the result of learned habituation, three aversive stimuli were used. A high concentration of the particular antifeedant, xanthotoxin, acted as a noxious stimulus and dishabituated (reversed) the decrement in the antifeedant response to M. volkensii. Cold shock or CO₂ was marginally effective in dishabituating the response. The fact that the decrease in antifeedant response can be dishabituated has implications for pest management.     

Herbivore overlap and competition in Kenya rangelands

Small herbivores such as lagomorphs, rodents and orthopterans are important consumers in grasslands. Techniques of data collection by microscope analysis of stomach contents and quantitative analysis of results are presented for assessing dietary overlap and potential competition for food resources among different classes of herbivores. Example analysis of data for small herbivores and ungulates from an area south of Nairobi National Park, Kenya, are presented. In the average growing season, diet overlap between angulates and small herbivores is low, and therefore, potential for competition slight. Considering sesonal variation in food resources availability and extreme shortages documented for occasional seasons, it is probable that periodic competition occurs. Hares are potentially the greatest competitors with ungulates in such conditions, because of their wide niche breadth and spatial overlap with ungulates. Assessment of the degree and implications of periodic competitive interactions requires careful analysis of niche breadth and overlap on the food resource gradient based upon a spatial and temporal evaluation of habitat utilization.     

Herbivore specific induction of silica-based plant defences

Induced plant responses to herbivory have major impacts on herbivore feeding behaviour, performance and population dynamics. These effects are well established for chemical defences, but induction of physical defences remains far less studied. However, for many plants, it is physical defences that play the major role in regulating the levels of herbivore damage sustained. We provide evidence that, in grasses, induction of physical defences is both specific to herbivore feeding, as opposed to mechanical damage, and may be dependant on the amount of damage imposed. Furthermore, we show that the magnitude of the induction response is sufficient to deter further damage and affect herbivore performance. We compared silica induction in two grass species in response to vertebrate and invertebrate damage, and to mechanical defoliation. Induction was assessed at two levels of damage over 16 months. Foliar silica content did not increase in response to mechanical defoliation, but damage by either voles or locusts resulted in increases in silica content of over 400%. This increase deterred feeding by both voles and locusts. Silica induction in grasses due to repeated damage events over a prolonged period suggests a possible role for silica defence in the cyclical population fluctuations observed in many grass-feeding herbivores.     

How Herbivore Browsing Strategy Affects Whole-Plant Photosynthetic Capacity

If a browse damage index indicates that a tree has been 50% browsed by herbivores, does this mean half the leaves are entirely eaten or are all the leaves half eaten? Were the affected leaves old or young? Large or small? In sunshine or shade? Understanding what effect browsing will have on the photosynthetic capacity and the plant’s survival ability clearly requires a greater understanding of browsing strategy across the canopy than can be given by a single index value. We developed stochastic models of leaf production, growth and consumption using data from kamahi (Weinmannia racemosa) trees in New Zealand which have been browsed by possums (Trichosurus vulpecula), to ascertain which of six feasible browsing strategies possums are most likely to be employing. We compared the area distribution of real fallen leaves to model output in order to select the best model, and used the model to predict the age distribution of leaves on the tree and thus infer its photosynthetic capability. The most likely browsing strategy that possums employ on kamahi trees is a preference for virgin (i.e. previously unbrowsed) leaves, consistent with the idea that browsing increases the production of chemical plant defences. More generally, our results show that herbivore browsing strategy can significantly change the whole-plant photosynthetic capability of any plant and hence its ability to survive, and therefore, herbivore damage indices should be used in conjunction with more detailed information about herbivore browsing strategy.     

An Insect Herbivore Microbiome with High Plant Biomass-Degrading Capacity

Herbivores can gain indirect access to recalcitrant carbon present in plant cell walls through symbiotic associations with lignocellulolytic microbes. A paradigmatic example is the leaf-cutter ant (Tribe: Attini), which uses fresh leaves to cultivate a fungus for food in specialized gardens. Using a combination of sugar composition analyses, metagenomics, and whole-genome sequencing, we reveal that the fungus garden microbiome of leaf-cutter ants is composed of a diverse community of bacteria with high plant biomass-degrading capacity. Comparison of this microbiome''s predicted carbohydrate-degrading enzyme profile with other metagenomes shows closest similarity to the bovine rumen, indicating evolutionary convergence of plant biomass degrading potential between two important herbivorous animals. Genomic and physiological characterization of two dominant bacteria in the fungus garden microbiome provides evidence of their capacity to degrade cellulose. Given the recent interest in cellulosic biofuels, understanding how large-scale and rapid plant biomass degradation occurs in a highly evolved insect herbivore is of particular relevance for bioenergy.     

Generalist Herbivore Foraging and Its Role in Competitive Interactions

Whether herbivores are food limited and compete interspecificallyfor food has been debated by population/community ecologists.To examine this proposition, a mechanistic approach based uponautecological observations is employed:

1. 45 foraging studies of 20 species of generalist herbivores indicatethat the herbivores behave as energy maximizers in their dietselection, as determined by a linear programming model.
2. Theconstraints that determine the forager's energy maximizingdietcan be used to determine whether a food item should beconsumed,based upon a minimum digestibility that determinesenergy valueand a minimum item size or abundance that determinescroppingrate.
3. Population densities of a number of herbivore speciesdependupon the biomass of plants in the environment that satisfytheminimum characteristics sought by the herbivore.
4. Usingexperimental populations for several herbivore speciesthatare known to be food limited, it can be demonstrated thatthesespecies compete with each other. The competitive isoclinesarenon-linear and arise from the fractions of each forager'sfoodresources that it shares and exclusively uses, which dependupon each species' minimum food characteristics.
5. The resultsindicate that a mechanistic approach can provideconsiderableinsights into herbivore community structure. Theforaging constraintsunderlying the entire analysis may be bodysize dependent, providinga more general view.

     

Herbivore regulation and irreversible vegetation change in semi-arid grazing systems

Models made to explain sudden and irreversible vegetation shifts in semi-arid grasslands typically assume that herbivore density is independent of the state of the vegetation, e.g., under the control of humans. We relax this assumption and investigate the mathematical implications of vegetation-regulated herbivore population dynamics. We show that irreversible vegetation change may also occur in systems where herbivore population dynamics are affected by changes in plant standing crop. Our analysis furthermore shows that irreversible vegetation change may occur for a larger set of soil and climatic conditions when herbivore numbers are independent of the vegetation, as compared to systems where vegetation density determines herbivore population size. Hence, our analysis suggests that irreversible vegetation change is less likely to occur in systems with natural herbivore population dynamics than in systems where humans control herbivore density.     

Non-Photochemical Quenching Capacity in Arabidopsis thaliana Affects Herbivore Behaviour

Under natural conditions, plants have to cope with numerous stresses, including light-stress and herbivory. This raises intriguing questions regarding possible trade-offs between stress defences and growth. As part of a program designed to address these questions we have compared herbivory defences and damage in wild type Arabidopsis thaliana and two “photoprotection genotypes”, npq4 and oePsbS, which respectively lack and overexpress PsbS (a protein that plays a key role in qE-type non-photochemical quenching). In dual-choice feeding experiments both a specialist (Plutella xylostella) and a generalist (Spodoptera littoralis) insect herbivore preferred plants that expressed PsbS most strongly. In contrast, although both herbivores survived equally well on each of the genotypes, for oviposition female P. xylostella adults preferred plants that expressed PsbS least strongly. However, there were no significant differences between the genotypes in levels of the 10 most prominent glucosinolates; key substances in the Arabidopsis anti-herbivore chemical defence arsenal. After transfer from a growth chamber to the field we detected significant differences in the genotypes’ metabolomic profiles at all tested time points, using GC-MS, but no consistent “metabolic signature” for the lack of PsbS. These findings suggest that the observed differences in herbivore preferences were due to differences in the primary metabolism of the plants rather than their contents of typical “defence compounds”. A potentially significant factor is that superoxide accumulated most rapidly and to the highest levels under high light conditions in npq4 mutants. This could trigger changes in planta that are sensed by herbivores either directly or indirectly, following its dismutation to H₂O₂.     

Herbivore effects on developmental instability and fecundity of holm oaks

Plants are able to compensate for loss of tissue due to herbivores at a variety of spatial and temporal scales, masking detrimental effects of herbivory on plant fitness at these scales. The stressing effect of herbivory could also produce instability in the development of plant modules, and measures of such instability may reflect the fitness consequences of herbivory if instability is related to components of plant fitness. We analyse the relationships between herbivory, developmental instability and production of female flowers and fruits of holm oak Quercus ilex trees by means of herbivore removal experiments. Removal of leaf herbivores reduced herbivory rates at the tree level, but had no effect on mean production of female flowers or mature fruits, whereas herbivory tended to enhance flower production and had no effect on fruit abortion at the shoot level. Differences in herbivory levels between shoots of the same branch did not affect the size and fluctuating asymmetry of intact leaves. These results indicate compensation for herbivory at the tree level and over-compensation at the shoot level in terms of allocation of resources to female flower production. Removal of insect herbivores produced an increase in the mean developmental instability of leaves at the tree level in the year following the insecticide treatment, and there was a direct relationship between herbivory rates in the current year and leaf fluctuating asymmetry the following year irrespective of herbivore removal treatment. Finally, the production of pistillate flowers and fruits by trees was inversely related to the mean fluctuating asymmetry of leaves growing the same year. Leaf fluctuating asymmetry was thus an estimator of the stressing effects of herbivory on adult trees, an effect that was delayed to the following year. As leaf fluctuating asymmetry was also related to tree fecundity, asymmetry levels provided a sensitive measure of plant performance under conditions of compensatory responses to herbivory.     

A Latex Metabolite Benefits Plant Fitness under Root Herbivore Attack

Plants produce large amounts of secondary metabolites in their shoots and roots and store them in specialized secretory structures. Although secondary metabolites and their secretory structures are commonly assumed to have a defensive function, evidence that they benefit plant fitness under herbivore attack is scarce, especially below ground. Here, we tested whether latex secondary metabolites produced by the common dandelion (Taraxacum officinale agg.) decrease the performance of its major native insect root herbivore, the larvae of the common cockchafer (Melolontha melolontha), and benefit plant vegetative and reproductive fitness under M. melolontha attack. Across 17 T. officinale genotypes screened by gas and liquid chromatography, latex concentrations of the sesquiterpene lactone taraxinic acid β-D-glucopyranosyl ester (TA-G) were negatively associated with M. melolontha larval growth. Adding purified TA-G to artificial diet at ecologically relevant concentrations reduced larval feeding. Silencing the germacrene A synthase ToGAS1, an enzyme that was identified to catalyze the first committed step of TA-G biosynthesis, resulted in a 90% reduction of TA-G levels and a pronounced increase in M. melolontha feeding. Transgenic, TA-G-deficient lines were preferred by M. melolontha and suffered three times more root biomass reduction than control lines. In a common garden experiment involving over 2,000 T. officinale individuals belonging to 17 different genotypes, high TA-G concentrations were associated with the maintenance of high vegetative and reproductive fitness under M. melolontha attack. Taken together, our study demonstrates that a latex secondary metabolite benefits plants under herbivore attack, a result that provides a mechanistic framework for root herbivore driven natural selection and evolution of plant defenses below ground.     

The Root Herbivore History of the Soil Affects the Productivity of a Grassland Plant Community and Determines Plant Response to New Root Herbivore Attack

Insect root herbivores can alter plant community structure by affecting the competitive ability of single plants. However, their effects can be modified by the soil environment. Root herbivory itself may induce changes in the soil biota community, and it has recently been shown that these changes can affect plant growth in a subsequent season or plant generation. However, so far it is not known whether these root herbivore history effects (i) are detectable at the plant community level and/or (ii) also determine plant species and plant community responses to new root herbivore attack. The present greenhouse study determined root herbivore history effects of click beetle larvae (Elateridae, Coleoptera, genus Agriotes) in a model grassland plant community consisting of six common species (Achillea millefolium, Plantago lanceolata, Taraxacum officinale, Holcus lanatus, Poa pratensis, Trifolium repens). Root herbivore history effects were generated in a first phase of the experiment by growing the plant community in soil with or without Agriotes larvae, and investigated in a second phase by growing it again in the soils that were either Agriotes trained or not. The root herbivore history of the soil affected plant community productivity (but not composition), with communities growing in root herbivore trained soil producing more biomass than those growing in untrained soil. Additionally, it influenced the response of certain plant species to new root herbivore attack. Effects may partly be explained by herbivore-induced shifts in the community of arbuscular mycorrhizal fungi. The root herbivore history of the soil proved to be a stronger driver of plant growth on the community level than an actual root herbivore attack which did not affect plant community parameters. History effects have to be taken into account when predicting the impact of root herbivores on grasslands.     

Mistletoes Facilitate a Desert Herbivore by Improving the Quality of Shade

Ecosystems - In arid environments, shade provided by vegetation forms the crux of many facilitation pathways by providing other organisms with relief from high levels of solar radiation and extreme...     

Individual Specialization to Non-Optimal Hosts in a Polyphagous Marine Invertebrate Herbivore

Factors determining the degree of dietary generalism versus specialism are central in ecology. Species that are generalists at the population level may in fact be composed of specialized individuals. The optimal diet theory assumes that individuals choose diets that maximize fitness, and individual specialization may occur if individuals'' ability to locate, recognize, and handle different food types differ. We investigate if individuals of the marine herbivorous slug Elysia viridis, which co-occur at different densities on several green macroalgal species in the field, are specialized to different algal hosts. Individual slugs were collected from three original algal host species (Cladophora sericea, Cladophora rupestris and Codium fragile) in the field, and short-term habitat choice and consumption, as well as long-term growth (proxy for fitness), on four algal diet species (the original algal host species and Chaetomorpha melagonium) were studied in laboratory experiments. Nutritional (protein, nitrogen, and carbon content) and morphological (dry weight, and cell/utricle volume) algal traits were also measured to investigate if they correlated with the growth value of the different algal diets. E. viridis individuals tended to choose and consume algal species that were similar to their original algal host. Long-term growth of E. viridis, however, was mostly independent of original algal host, as all individuals reached a larger size on the non-host C. melagonium. E. viridis growth was positively correlated to algal cell/utricle volume but not to any of the other measured algal traits. Because E. viridis feeds by piercing individual algal cells, the results indicate that slugs may receive more cytoplasm, and thus more energy per unit time, on algal species with large cells/utricles. We conclude that E. viridis individuals are specialized on different hosts, but host choice in natural E. viridis populations is not determined by the energetic value of seaweed diets as predicted by the ODT.