Search

Background and Aims: The deposition of atmospheric nitrogen has increased globally and interfered with plant growth and development. However, only a few studies have examined the influence of atmospheric nitrogen deposition on plant–herbivore interactions in the framework of plant invasion, and the underlying mechanisms remain unclear. Methods: In this study, we examined the changes in growth and herbivore resistance of the invasive weed Alternanthera philoxeroides and its native co-occurring congener Alternanthera sessilis in response to simulated nitrogen deposition. We further investigated the competitive ability of these two plant species grown in mono- and mix-culture conditions with or without herbivore pressures. Results: The results indicated that simulated nitrogen deposition largely increased the growth of both plant species, while A. philoxeroides produced more biomass than A. sessilis. The specialist and generalist herbivores showed contrasting preferences for the two plant species in the controls, whereas A. philoxeroides showed greater resistance to both herbivore species under simulated nitrogen deposition. Further investigation of host plant traits related to leaf structural and chemical defences suggested that such difference in herbivore resistance between the two plant species could be attributed to the increased levels of structural defense in A. philoxeroides and reduced levels of defensive metabolites in A. sessilis. The inter-specific competition test revealed that simulated nitrogen deposition largely increased the competitive advantage of A. philoxeroides over A. sessilis, regardless of the presence or absence of herbivores. Conclusion: Our study suggests that the invasiveness of A. philoxeroides may be enhanced by increased atmospheric nitrogen deposition. [ABSTRACT FROM AUTHOR]

Arthropod pests cause significant problems in agricultural crops all around the world. As chemical pesticide use becomes less desired, there is a need for alternative methods of pest control. Inspired by the natural adhesiveness of arthropod trapping plants, we examined the effectiveness of adhesive droplets made from oxidised and cross-linked plant-derived oils for control of western flower thrips. Two filter paper droplet adhesiveness assays and three detached chrysanthemum leaf assays were carried out to test efficacy against thrips. Suspensions containing adhesive droplets and other constituents were applied to filter papers and leaves via spraying or dipping. On filter papers, droplets made from oxidised rice germ oil (RGO) of different sizes caught 40–93% of thrips. Droplets made of a mixture of sunflower, olive, and linseed oil (MIX) caught up to 94% of thrips. Likewise, adhesive droplet-treated filter papers showed higher thrips mortality than untreated or control solution-treated filter papers. On chrysanthemum leaves, thrips were caught by both RGO (up to 40%) and MIX droplets (up to 20%) and thrips damage and reproduction were reduced. On MIX-treated leaves, thrips mortality was also increased. Within treatments, droplets of different size classes occurred and larger droplets were more effective at catching thrips in general. Droplets were also robust to rinsing with water, which is of importance for their application in horticulture. In conclusion, adhesive droplets made from edible plant oils show potential for use in control of western flower thrips. [ABSTRACT FROM AUTHOR]

Aims: Plants can influence the level of herbivory experienced by neighboring plants. The importance of such belowground associational effects are poorly understood. In this study we examine whether Jacobaea vulgaris provides associational resistance against nematodes to neighboring plants. Methods: Thirteen species (6 forbs, 3 grasses and 4 legumes) were each grown in mixtures with J. vulgaris and in monocultures. A nematode community was introduced to half of the pots. After 12 weeks, plant dry mass was assessed for each individual plant in each pot, and the number of nematodes in the soil and roots were identified. We then examined for each plant species its performance in mixtures and in monocultures, in presence and absence of nematodes and analyzed the abundance and composition of nematodes. Results: Forbs produced more, grasses similar, and legumes less biomass in mixtures with J. vulgaris than in monocultures. Nematode addition did not influence biomass. There were fewer root-feeding nematodes in the soil in mixtures than in monocultures, but this was only true for plants that were good hosts for nematodes. The community composition of soil nematodes was different in monocultures and mixtures. Densities of migratory endoparasitic nematodes in the roots of neighboring plants were lower in mixtures than in monocultures. Moreover, the presence of nematodes changed the outcome of plant-plant interactions, often in favor of J. vulgaris. Conclusions: Jacobaea vulgaris provides belowground associational resistance to other plants against migratory endoparasitic nematodes, and the presence of nematodes can change the outcome of plant-plant interactions. [ABSTRACT FROM AUTHOR]

Background and aims: Jacobaea vulgaris plants grow better in sterilized than in live soil. Foliar application of SA mitigates this negative effect of live soil on plant growth. To examine what causes the positive effect of SA application on plant growth in live soils, we analyzed the effects of SA application on the composition of active rhizosphere bacteria in the soil. Methods: We studied the composition of the microbial community over four consecutive plant cycles (generations), using mRNA sequencing of the microbial communities in the rhizosphere of J. vulgaris. We initiated the experiment with an inoculum of live soil collected from the field, and at the start of each subsequent plant cycle, we inoculated a small part of the soil from the previous plant cycle into sterile bulk soil. Results: Application of SA did not significantly increase or decrease the Shannon diversity at genus level within each generation, but several specific genera were enriched or depleted after foliar SA application. The composition of bacterial communities in the rhizosphere significantly differed between plant cycles (generations), but application of SA did not alter this pattern. In the first generation no genera were significantly affected by the SA treatment, but in the second, third and fourth generations, specific genera were significantly affected. 89 species out of the total 270 (32.4%) were present as the "core" microbiome in all treatments over four plant cycles. Conclusions: Overall, our study shows that the composition of bacterial genera in the rhizosphere significantly differed between plant cycles, but that it was not strongly affected by foliar application of SA on J. vulgaris leaves. Further studies should examine how activation of the SA signaling pathway in the plant changes the functional genes of the rhizosphere bacterial community. [ABSTRACT FROM AUTHOR]

Abiotic and biotic properties of soil can influence growth and chemical composition of plants. Although it is well-known that soil microbial composition can vary greatly spatially, how this variation affects plant chemical composition is poorly understood. We grew genetically identical Jacobaea vulgaris in sterilized soil inoculated with live soil collected from four natural grasslands and in 100% sterilized soil. Within each grassland we sampled eight plots, totalling 32 different inocula. Two samples per plot were collected, leading to three levels of spatial variation: within plot, between and within grasslands. The leaf metabolome was analysed with 1H Nuclear magnetic resonance spectroscopy (NMR) to investigate if inoculation altered the metabolome of plants and how this varied between and within grasslands. Inoculation led to changes in metabolomics profiles of J. vulgaris in two out of four sites. Plants grown in sterilized and inoculated soils differed in concentrations of malic acid, tyrosine, trehalose and two pyrrolizidine alkaloids (PA). Metabolomes of plants grown in inoculated soils from different sites varied in glucose, malic acid, trehalose, tyrosine and in one PA. The metabolome of plants grown in soils with inocula from the same site was more similar than with inocula from distant sites. We show that soil influences leaf metabolomes. Performance of aboveground insects often depends on chemical composition of plants. Hence our results imply that soil microbial communities, via affecting aboveground plant metabolomes, can impact aboveground plant-insect food chains but that it is difficult to make general predictions due to spatial variation in soil microbiomes. [ABSTRACT FROM AUTHOR]

Aims: The spread of invasive weeds threatens biodiversity and stability of ecosystems. Jacobaea vulgaris is an invasive weed in some countries and an outbreak species in its native European range. Although biological control using specialist herbivores is available, controlling with soil microorganisms remains far less explored.Twenty bacteria strains isolated from roots of J. vulgaris were used to examine bacterial effects on seed germination, root morphology and early plant growth. Moreover, we tested direct effects of the bacteria on a specialist herbivore of J. vulgaris, the leaf chewing caterpillar (Tyria jacobaeae), commonly used in biocontrol. We also tested indirect effects of bacteria, via the plant, on the performance of T. jacobaeae and the aphid species Aphis jacobaeae. Lastly, we examined the host specificity of two tested bacteria on three other forbs.Two Gammaproteobacteria, Pseudomonas brassicacearum and Serratia plymuthica, significantly reduced root growth of seedlings in-vitro, while seed germination was unaffected. However, these negative effects were observed across other forb species as well. Bacillus spp. injection led to the highest T. jacobaeae caterpillar mortality, while ingestion had no effect. Inoculation of the plants with bacteria did not affect aphid performance, but significantly affected T. jacobaeae preference. Specifically, P. syringae and one Bacillus sp. strain significantly increased T. jacobaeae preference.Our results show that two root-associated bacteria inhibit J. vulgaris growth, but their lack of host specificity restricts their potential for biocontrol. Our study also highlights that belowground microorganisms can hamper or enhance the performance of aboveground insects.Methods: The spread of invasive weeds threatens biodiversity and stability of ecosystems. Jacobaea vulgaris is an invasive weed in some countries and an outbreak species in its native European range. Although biological control using specialist herbivores is available, controlling with soil microorganisms remains far less explored.Twenty bacteria strains isolated from roots of J. vulgaris were used to examine bacterial effects on seed germination, root morphology and early plant growth. Moreover, we tested direct effects of the bacteria on a specialist herbivore of J. vulgaris, the leaf chewing caterpillar (Tyria jacobaeae), commonly used in biocontrol. We also tested indirect effects of bacteria, via the plant, on the performance of T. jacobaeae and the aphid species Aphis jacobaeae. Lastly, we examined the host specificity of two tested bacteria on three other forbs.Two Gammaproteobacteria, Pseudomonas brassicacearum and Serratia plymuthica, significantly reduced root growth of seedlings in-vitro, while seed germination was unaffected. However, these negative effects were observed across other forb species as well. Bacillus spp. injection led to the highest T. jacobaeae caterpillar mortality, while ingestion had no effect. Inoculation of the plants with bacteria did not affect aphid performance, but significantly affected T. jacobaeae preference. Specifically, P. syringae and one Bacillus sp. strain significantly increased T. jacobaeae preference.Our results show that two root-associated bacteria inhibit J. vulgaris growth, but their lack of host specificity restricts their potential for biocontrol. Our study also highlights that belowground microorganisms can hamper or enhance the performance of aboveground insects.Results: The spread of invasive weeds threatens biodiversity and stability of ecosystems. Jacobaea vulgaris is an invasive weed in some countries and an outbreak species in its native European range. Although biological control using specialist herbivores is available, controlling with soil microorganisms remains far less explored.Twenty bacteria strains isolated from roots of J. vulgaris were used to examine bacterial effects on seed germination, root morphology and early plant growth. Moreover, we tested direct effects of the bacteria on a specialist herbivore of J. vulgaris, the leaf chewing caterpillar (Tyria jacobaeae), commonly used in biocontrol. We also tested indirect effects of bacteria, via the plant, on the performance of T. jacobaeae and the aphid species Aphis jacobaeae. Lastly, we examined the host specificity of two tested bacteria on three other forbs.Two Gammaproteobacteria, Pseudomonas brassicacearum and Serratia plymuthica, significantly reduced root growth of seedlings in-vitro, while seed germination was unaffected. However, these negative effects were observed across other forb species as well. Bacillus spp. injection led to the highest T. jacobaeae caterpillar mortality, while ingestion had no effect. Inoculation of the plants with bacteria did not affect aphid performance, but significantly affected T. jacobaeae preference. Specifically, P. syringae and one Bacillus sp. strain significantly increased T. jacobaeae preference.Our results show that two root-associated bacteria inhibit J. vulgaris growth, but their lack of host specificity restricts their potential for biocontrol. Our study also highlights that belowground microorganisms can hamper or enhance the performance of aboveground insects.Conclusions: The spread of invasive weeds threatens biodiversity and stability of ecosystems. Jacobaea vulgaris is an invasive weed in some countries and an outbreak species in its native European range. Although biological control using specialist herbivores is available, controlling with soil microorganisms remains far less explored.Twenty bacteria strains isolated from roots of J. vulgaris were used to examine bacterial effects on seed germination, root morphology and early plant growth. Moreover, we tested direct effects of the bacteria on a specialist herbivore of J. vulgaris, the leaf chewing caterpillar (Tyria jacobaeae), commonly used in biocontrol. We also tested indirect effects of bacteria, via the plant, on the performance of T. jacobaeae and the aphid species Aphis jacobaeae. Lastly, we examined the host specificity of two tested bacteria on three other forbs.Two Gammaproteobacteria, Pseudomonas brassicacearum and Serratia plymuthica, significantly reduced root growth of seedlings in-vitro, while seed germination was unaffected. However, these negative effects were observed across other forb species as well. Bacillus spp. injection led to the highest T. jacobaeae caterpillar mortality, while ingestion had no effect. Inoculation of the plants with bacteria did not affect aphid performance, but significantly affected T. jacobaeae preference. Specifically, P. syringae and one Bacillus sp. strain significantly increased T. jacobaeae preference.Our results show that two root-associated bacteria inhibit J. vulgaris growth, but their lack of host specificity restricts their potential for biocontrol. Our study also highlights that belowground microorganisms can hamper or enhance the performance of aboveground insects. [ABSTRACT FROM AUTHOR]

In this study we investigated the effect of methyl jasmonate (MeJA) application on pyrrolizidine alkaloid (PA) concentration and composition of two closely related Jacobaea species. In addition, we examined whether MeJA application affected herbivory of the polyphagous leaf feeding herbivore Spodoptera exigua. A range of concentrations of MeJA was added to the medium of Jacobaea vulgaris and J. aquatica tissue culture plants grown under axenic conditions. PA concentrations were measured in roots and shoots using LC-MS/MS. In neither species MeJA application did affect the total PA concentration at the whole plant level. In J. vulgaris the total PA concentration decreased in roots but increased in shoots. In J. aquatica a similar non-significant trend was observed. In both Jacobaea species MeJA application induced a strong shift from senecionine- to erucifoline-like PAs, while the jacobine- and otosenine-like PAs remained largely unaffected. The results show that MeJA application does not necessarily elicits de novo synthesis, but rather leads to PA conversion combined with reallocation of certain PAs from roots to shoots. S. exigua preferred feeding on control leaves of J. aquatica over MeJA treated leaves, while for J. vulgaris both the control and MeJA treated leaves were hardly eaten. This suggests that the MeJA-induced increase of erucifoline-like PAs can play a role in resistance of J. aquatica to S. exigua. In J. vulgaris resistance to S. exigua may already be high due to the presence of jacobine-like PAs or other resistance factors. [ABSTRACT FROM AUTHOR]

Plants produce an extremely diverse array of metabolites that mediate many aspects of plant-environment interactions. In the context of plant-herbivore interactions, it is as yet poorly understood how natural backgrounds shape the bioactivity of individual metabolites. We tested the effects of a methanol extract of Jacobaea plants and five fractions derived from this extract, on survival of western flower thrips (WFT). When added to an artificial diet, the five fractions all resulted in a higher WFT survival rate than the methanol extract. In addition, their expected combined effect on survival, assuming no interaction between them, was lower than that of the methanol extract. The bioactivity was restored when the fractions were combined again in their original proportion. These results strongly suggest synergistic interactions among the fractions on WFT survival rates. We then tested the effects of two pyrrolizidine alkaloids (PAs), free base retrorsine and retrorsine N-oxide, alone and in combination with the five shoot fractions on WFT survival. The magnitude of the effects of the two PAs depended on the fraction to which they were added. In general, free base retrorsine was more potent than retrorsine N-oxide, but this was contingent on the fraction to which these compounds were added. Our results support the commonly held, though seldom tested, notion that the efficacy of plant metabolites with respect to plant defence is dependent on their phytochemical background. It also shows that the assessment of bioactivity cannot be decoupled from the natural chemical background in which these metabolites occur. [ABSTRACT FROM AUTHOR]

Introduction: Usually whole plant or whole leaf extracts are analyzed to study the chemical ecology of insect-plant interactions. For herbivore species the contact with the leaf surface enables them to estimate the quality of the plant. The relationship between the leaf-surface and leaf-tissue secondary metabolites (SMs) could offer important new insights in insect-plant interactions mediated by SMs. Pyrrolizidine alkaloids (PAs), typical defense chemicals in Jacobaea species, are repellent for generalist herbivores but are attractive to specialists. Objectives: Explore whether the PAs on the leaf surface are a reliable representation of the PAs in the leaf tissue in PA-containing plants. Method: The concentration of individual PAs present on the leaf surface and in the corresponding leaf tissue from 37 genotypes (one plant from each genotype) of an F generation of a cross between Jacobaea vulgaris and Jacobaea aquatica was measured by high performance liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). PAs were removed from the leaf surface by extraction with a slightly acidic aqueous solution. Results: The total amount of PAs present on the surface of the leaves was only 0.015% (range 0.001-0.163%) of the total amount present in the leaf tissue. Most PAs present in the leaf tissue were also found on the surface, except for jaconine, dehydrojaconine, dehydrojacoline and usaramine N-oxide. Positive correlations between leaf-surface and leaf-tissue concentrations were found for most of the jacobine-like and otosenine-like PAs, but correlations for total PA, senecionine- and erucifoline-like PAs were not significant. Conclusion: These results indicate that PA variation on the leaf surface only partially reflects the PA variation in the leaf tissue. Because most herbivores are affected in a different manner by individual PAs, this result means that the leaf surface does not give a reliable estimate of plant quality to herbivores. [ABSTRACT FROM AUTHOR]

According to the Shifting Defense Hypothesis, invasive plants should trade-off their costly quantitative defense to cheaper qualitative defense and growth due to the lack of natural specialist enemies and the presence of generalist enemies in the introduced areas. Several studies showed that plant genotypes from the invasive areas had a better qualitative defense than genotypes from the native area but only a few studies have focused on the quantitative defenses and tolerance ability. We compared structural defenses, tolerance and growth between invasive and native plant populations from different continents using the model plant Jacobaea vulgaris. We examined several microscopical structure traits, toughness, amount of cell wall proteins, growth and root-shoot ratio, which is a proxy for tolerance. The results show that invasive Jacobaea vulgaris have thinner leaves, lower leaf mass area, lower leaf cell wall protein contents and a lower root-shoot ratio than native genotypes. It indicates that invasive genotypes have poorer structural defense and tolerance to herbivory but potentially higher growth compared to native genotypes. These findings are in line with the Evolution of Increased Competitive Ability hypothesis and Shifting Defense Hypothesis. We also show that the invasiveness of this species in three geographically separated regions is consistently associated with the loss of parts of its quantitative defense and tolerance ability. The simultaneous change in quantitative defense and tolerance of the same magnitude and direction in the three invasive regions can be explained by parallel evolution. We argue that such parallel evolution might be attributed to the absence of natural enemies rather than adaptation to local abiotic factors, since climate conditions among these three regions were different. Understanding such evolutionary changes helps to understand why plant species become invasive and might be important for biological control. [ABSTRACT FROM AUTHOR]

Plants produce a diversity of secondary metabolites (SMs) to protect them from generalist herbivores. On the other hand, specialist herbivores use SMs for host plant recognition, feeding and oviposition cues, and even sequester SMs for their own defense. Therefore, plants are assumed to face an evolutionary dilemma stemming from the contrasting effects of generalist and specialist herbivores on SMs. To test this hypothesis, bioassays were performed with F2 hybrids from Jacobaea species segregating for their pyrrolizidine alkaloids (PAs), using a specialist flea beetle ( Longitarsus jacobaeae) and a generalist slug ( Deroceras invadens). Our study demonstrated that while slug feeding damage was negatively correlated with the concentration of total PAs and that of senecionine-like PAs, flea beetle feeding damage was not affected by PAs. It was positively correlated though, with leaf fresh weight. The generalist slug was deterred by senecionine-like PAs but the specialist flea beetle was adapted to PAs in its host plant. Testing other herbivores in the same plant system, it was observed that the egg number of the specialist cinnabar moth was positively correlated with jacobine-like PAs, while the silver damage of generalist thrips was negatively correlated with senecionine- and jacobine-like PAs, and the pupae number of generalist leaf miner was negatively correlated with otosenine-like PAs. Therefore, while the specialist herbivores showed no correlation whatsoever with PA concentration, the generalist herbivores all showed a negative correlation with at least one type of PA. We concluded that the generalist herbivores were deterred by different structural groups of PAs while the specialist herbivores were attracted or adapted to PAs in its host plants. [ABSTRACT FROM AUTHOR]

Plants produce a variety of secondary metabolites (PSMs) that may be selective against herbivores. Yet, specialist herbivores may use PSMs as cues for host recognition, oviposition, and feeding stimulation, or for their own defense against parasites and predators. This summarizes a dual role of PSMs: deter generalists but attract specialists. It is not clear yet whether specialist herbivores are a selective force in the evolution of PSM diversity. A prerequisite for such a selective force would be that the preference and/or performance of specialists is influenced by PSMs. To investigate these questions, we conducted an oviposition experiment with cinnabar moths ( Tyria jacobaeae) and plants from an artificial hybrid family of Jacobaea vulgaris and Jacobaea aquatica. The cinnabar moth is a specialist herbivore of J. vulgaris and is adapted to pyrrolizidine alkaloids (PAs), defensive PSMs of these plants. The number of eggs and egg batches oviposited by the moths were dependent on plant genotype and positively correlated to concentrations of tertiary amines of jacobine-like PAs and some otosenine-like PAs. The other PAs did not correlate with oviposition preference. Results suggest that host plant PAs influence cinnabar moth oviposition preference, and that this insect is a potential selective factor against a high concentration of some individual PAs, especially those that are also involved in resistance against generalist herbivores. [ABSTRACT FROM AUTHOR]

At both a macro- and micro-evolutionary level, selection of and performance on host plants by specialist herbivores are thought to be governed partially by host plant chemistry. Thus far, there is little evidence to suggest that specialists can detect small structural differences in secondary metabolites of their hosts, or that such differences affect host choice or performance of specialists. We tested whether phytochemical differences between closely related plant species are correlated with specialist host choice. We conducted no-choice feeding trials using 17 plant species of three genera of tribe Senecioneae ( Jacobaea, Packera, and Senecio; Asteraceae) and a more distantly related species ( Cynoglossum officinale; Boraginaceae) containing pyrrolizidine alkaloids (PAs), and four PA-sequestering specialist herbivores of the genus Longitarsus (Chrysomelidae). We also assessed whether variation in feeding by specialist herbivores is attributable to different resource use strategies of the tested plant species. Plant resource use strategy was quantified by measuring leaf dry matter content, which is related to both plant nutritive value and to plant investment in quantitative defences. We found no evidence that intra-generic differences in PA profiles affect feeding by specialist herbivores. Instead, our results indicate that decisions to begin feeding are related to plant resource use strategy, while decisions to continue feeding are not based on any plant characteristics measured in this study. These findings imply that PA composition does not significantly affect host choice by these specialist herbivores. Leaf dry matter content is somewhat phylogenetically conserved, indicating that plants may have difficulty altering resource use strategy in response to selection pressure by herbivores and other environmental factors on an evolutionary time scale. [ABSTRACT FROM AUTHOR]

Hybridization between plant species can have a number of biological consequences; interspecific hybridization has been tied to speciation events, biological invasions, and diversification at the level of genes, metabolites, and phenotypes. This study aims to provide evidence of transgressive segregation in the expression of primary and secondary metabolites in hybrids between Jacobaea vulgaris and J. aquaticus using an NMR-based metabolomic profiling approach. A number of F hybrid genotypes exhibited metabolomic profiles that were outside the range encompassed by parental species. Expression of a number of primary and secondary metabolites, including jacaronone analogues, chlorogenic acid, sucrose, glucose, malic acid, and two amino acids was extreme in some F hybrid genotypes compared to parental genotypes, and citric acid was expressed in highest concentrations in J. vulgaris. Metabolomic profiling based on NMR is a useful tool for quantifying genetically controlled differences between major primary and secondary metabolites among plant genotypes. Interspecific plant hybrids in general, and specifically hybrids between J. vulgaris and J. aquatica, will be useful for disentangling the ecological role of suites of primary and secondary metabolites in plants, because interspecific hybridization generates extreme metabolomic diversity compared to that normally observed between parental genotypes. [ABSTRACT FROM AUTHOR]

Segregating plant hybrids often have more ecological and molecular variability compared to parental species, and are therefore useful for studying relationships between different traits, and the adaptive significance of trait variation. Hybrid systems have been used to study the relationship between the expression of plant defense compounds and herbivore susceptibility. We conducted a western flower thrips (WFT) bioassay using a hybrid family and investigated the relationship between WFT resistance and pyrrolizidine alkaloid (PA) variation. The hybrid family consisted of two parental ( Jacobaea vulgaris and Jacobaea aquatica) genotypes, two F genotypes, and 94 F hybrid lines. The J. aquatica genotype was more susceptible to thrips attack than the J. vulgaris genotype, the two F hybrids were as susceptible as J. aquatica, and susceptibility to WFT differed among F hybrid lines: 69 F lines were equally susceptible compared to J. aquatica, 10 F lines were more susceptible than J. aquatica and 15 F lines were as resistant as J. vulgaris or were intermediate to the two parental genotypes. Among 37 individual PAs that were derived from four structural groups (senecionine-, jacobine-, erucifoline- and otosenine-like PAs), the N-oxides of jacobine, jaconine, and jacoline were negatively correlated with feeding damage caused by WFT, and the tertiary amines of jacobine, jaconine, jacoline, and other PAs did not relate to feeding damage. Total PA concentration was negatively correlated with feeding damage. Among the four PA groups, only the total concentration of the jacobine-like PAs was negatively correlated with feeding damage. Multiple regression tests suggested that jacobine-like PAs play a greater role in WFT resistance than PAs from other structural groups. We found no evidence for synergistic effects of different PAs on WFT resistance. The relationship between PA variation and WFT feeding damage in the Jacobaea hybrids suggests a role for PAs in resistance to generalist insects. [ABSTRACT FROM AUTHOR]

Several theories have been developed to explain why invasive species are very successful and develop into pest species in their new area. The shifting defence hypothesis (SDH) argues that invasive plant species quickly evolve towards new defence levels in the invaded area because they lack their specialist herbivores but are still under attack by local (new) generalist herbivores. The SDH predicts that plants should increase their cheap, toxic defence compounds and lower their expensive digestibility reducing compounds. As a net result resources are saved that can be allocated to growth and reproduction giving these plants a competitive edge over the local plant species. We conducted a literature study to test whether toxic defence compounds in general are increased in the invaded area and if digestibility reducing compounds are lowered. We specifically studied the levels of pyrrolizidine alkaloids, a toxin which is known for its beneficial and detrimental impact against specialists and generalists, respectively. Digestibility reducers did not show a clear trend which might be due to the small number of studies and traits measured. The meta analysis showed that toxic compounds in general and pyrrolizidine alkaloid levels specifically, increased significantly in the invaded area, supporting the predictions of the SDH that a fast evolution takes place in the allocation towards defence. [ABSTRACT FROM AUTHOR]

The diversity of secondary metabolites (SMs) has been poorly understood from both a mechanistic and a functional perspective. Hybridization is suggested to contribute to the evolution of diversity of SMs. In this paper we discuss the effects of hybridization on SMs and herbivore resistance by evaluating the literature and with special reference to our own research results from the hybrids between Jacobaea vulgaris (syn. Senecio jacobaea) and Jacobaea aquatica (syn. Senecio aquaticus). We also review the possible genetic mechanism which causes the variation of SMs and herbivore resistance in hybrids. Most SMs in hybrids are present in the parents as well. But hybrids may miss some parental SMs or have novel SMs. The concentration of parental SMs in hybrids generally is constrained by that in parental plants, but transgressive expression was present in some hybrids. Hybrids may be as susceptible (resistant) as the parents or more susceptible than the parents, but rarely more resistant than the parents. However, different hybrid classes (F1, F2, backcrossing and mixed genotypes) show different patterns in relation to herbivore resistance. The variation in SMs and herbivore resistance occurring in hybrids could be explained by complicated genetic mechanisms rather than a simple one-gene model. Most previous work in this field only reported mean trait values for hybrid classes and few studies focused on genotype differences within hybrid classes. Our study in Jacobaea hybrids showed transgressive segregation in most SMs and herbivore resistance. To summarize, our article shows that hybridization may increase the variation of SMs and affect herbivore resistance, which may partially explain the evolution of chemical diversity in plants. [ABSTRACT FROM AUTHOR]

Differences in the herbivore community between a plant’s native (specialists and generalists) and introduced range (almost exclusively generalists) may lead to the evolution of reduced allocation to defences against specialist herbivores in the introduced range, allowing for increased allocation to competitive ability and to defences against generalist herbivores. Following this logic, the introduction of biological control agents should reverse this evolutionary shift and select for plants with life-history traits that are more similar to those of plants in the native range than those of plants in the introduced range that have not been exposed to biological control. In a common garden experiment, we compared performance and resistance traits of tansy ragwort, Jacobaea vulgaris, among populations from the introduced range (New Zealand and North America) that have either been exposed to or grown free from the biological control agent Longitarsus jacobaeae. For comparison, we included populations from the native European range. We found lower levels of generalist-deterrent pyrrolizidine alkaloids (PAs) and of soluble phenolics in New Zealand populations with than in populations without exposure to L. jacobaeae, while the opposite pattern was detected among North American populations. Contrary to expectation, populations with exposure to L. jacobaeae revealed more feeding damage by L. jacobaeae than populations without exposure. Introduced populations had higher levels of PAs and reproductive output than native J. vulgaris populations. Jacobaea vulgaris was introduced in different parts of the world some 100–130 years ago, while L. jacobaeae was introduced only some 20–40 years ago. Hence, the larger differences observed between native and introduced populations, as compared to introduced populations with and without biological control history, may result from different time scales available for selection to act. [ABSTRACT FROM AUTHOR]

We examined the effects of water and nutrient availability on the expression of the defense pyrrolizidine alkaloids (PAs) in Senecio jacobaea and S. aquaticus. Senecio jacobaea, and S. aquaticus are adapted to different natural habitats, characterized by differing abiotic conditions and different selection pressures from natural enemies. We tested if PA concentration and diversity are plastic over a range of water and nutrient treatments, and also whether such plasticity is dependent on plant species. We also tested the hypothesis that hybridization may contribute to PA diversity within plants, by comparing PA expression in parental species to that in artificially generated F1 hybrids, and also in later generation natural hybrids between S. jacobaea and S. aquaticus. We showed that total PA concentration in roots and shoots is not dependent on species, but that species determines the pattern of PA diversification. Pyrrolizidine alkaloid diversity and concentration are both dependent on environmental factors. Hybrids produce a putatively novel PA, and this PA is conserved in natural hybrids, that are backcrossed to S. jacobaea. Natural hybrids that are backcrossed several times to S. jacobaea are with regard to PA diversity significantly different from S. jacobaea but not from S. aquaticus, while F1 hybrids are in all cases more similar to S. jacobaea. These results collectively suggest that PA diversity is under the influence of natural selection. [ABSTRACT FROM AUTHOR]

In the Danish region of Kværkeby, a mutation in an, as yet, unknown single autosomal gene has resulted in a dominant resistance (R-) allele in the flea beetle Phyllotreta nemorum L. (Coleoptera: Chrysomelidae: Alticinae). It enables the beetle to overcome the defences of Barbarea vulgaris ssp. arcuata (Opiz.) Simkovics G-type (Brassicaceae) and use it as a host plant. In this study, we investigated the pleiotropic effects associated with the presence of this particular R-allele in female P. nemorum. These females had the R-allele backcrossed into the genetic background of non-resistant beetles. The effects were investigated under both favourable and stressful conditions (cold shock). The presence of the R-allele in a non-resistant genetic background caused a very high mortality in resistant individuals during the early stages of development under both conditions, but it did not affect the adult life-history traits longevity, body size and fecundity, under both conditions. Regardless of temperature treatment, resistant females in general were found to lay significantly more eggs. Developmental stability, as measured by tibia length fluctuating asymmetry, was not correlated with overall developmental stress in this study. [ABSTRACT FROM AUTHOR]

Examines pyrrolizidine alkaloids (PA) as oviposition stimulants for the cinnabar moth, Tyria jacobaeae. Preference of the moths of ovipositing on filter paper with a PA mixture extracted from Senecio jacobaea; Plant-insect interactions.

The ontogeny of pyrrolizidine alkaloid (PA) synthesis and constraints on defence level during the seedling stage were examined in the annual Senecio vulgaris and the monocarpic perennial Senecio jacobaea. In both species, PAs were actively synthesized from the onset of seedling growth so that juvenile stages did not go through an undefended stage. Roots are known to be the exclusive sites where PAs are produced. Root biomass was the single most important biomass parameter explaining variation in total PAs per seedling. All correlation coefficients between—relative growth rate and PA concentration were negative, but none was significant. However, a significant negative—correlation was found between shoot to root ratio and PA concentration in S. jacobaeaseedlings, suggesting a dilution effect of the PAs. Earlier studies have shown that the shoot to root ratio is positively correlated with relative growth—rate of established S. jacobaea plants. It is therefore suggested that young S. jacobaea plants with a high shoot to root ratio and hence a high growth capacity necessarily have lower PA defence levels than plants with a low shoot to root ratio. [ABSTRACT FROM AUTHOR]

The evolution of the diversity of related secondary metabolites in plants is still poorly understood. It is often thought that the evolution of plant secondary metabolites is driven by specialist insect herbivores and under this coevolutionary model it is expected that related compounds differ in their effects on specialist herbivores. Here we focus on the diversity of pyrrolizidine alkaloids (PAs) in Senecio species and their effects on Tyria jacobaeae, a specialist moth on Senecio jacobaea. As a first step to determine the effects of related PAs on T. jacobaeae, we studied larval performance on plants from 11 S. jacobaea populations and eight Senecio species with different PA compositions. Although the populations of S. jacobaea differed in their PA compositions, there was no difference in larval performance among the populations. Larval performance differed among the eight species but we could not show a correlation with PA composition. Oviposition choice experiments showed a strong correlation between oviposition preference and larval performance on the eight species but oviposition preference did not seem to be correlated with PAs. We found no indications that related PAs differ in effects on the specialist T. jacobaeae; therefore it seems unlikely that T. jacobaeae is a driving force behind the evolution of the diversity of PAs. Alternatively, we propose that the evolution of the diversity of PAs is driven by selection pressure from generalist herbivores or that the diversity of PAs may even be selectively neutral. [ABSTRACT FROM AUTHOR]

Presents a study on an alternative method for the detection of Amplified Fragment Length Polymorphisms (AFLPs) in three plant species. Materials and chemicals utilized in the study; Procedures on DNA extraction; Procedures on AFLP reactions.

The constitutive pyrrolizidine alkaloid (PA) concentration of both shoots and roots differed significantly between 17 selfed families. The broad-sense heritability accounted for 33-43% of the variation in PA levels. Families also differed significantly in the amount and the direction of PA induction in both shoots and roots, 24 h after punching 15 holes in the leaves. We found a significantly negative relationship between the changes in PA content of the shoots and changes in PA content of the roots. The total PA content of the plants did not increase. We thus concluded that changes in PA distribution over the plant resulted from transport of PAs within the plant. The direction of transport differed between families: some transported PAs to the shoots, others to the roots. This makes it questionable whether PAs act as damage-induced defences. The effect of damage on the PA concentration is far less than the differences found between families in the constitutive PA concentration. This again strongly suggests that damage-induced defences in Cynoglossum officinale do not play an important role. We argue that the general lack of attention that is given to genotype in induction experiments, has led to false conclusions. [ABSTRACT FROM AUTHOR]

We hypothesize that the tritrophic interaction between ants, the aphid Aphis jacobaeae, the moth Tyria jacobaeae, and the plant Senecio jacobaea can explain the genetic variation observed in pyrrolizidine alkaloid concentration in natural populations of S. jacobaea. The ant Lasius niger effectively defends S. jacobaea plants infested with A. jacobaeae against larvae of T. jacobaeae. S. jacobaea plants with A. jacobaeae which are defended by ants escape regular defoliation by T. jacobaeae. Plants with aphids and ants have a lower pyrrolizidine alkaloid concentration than plants without aphids and ants. When these data are fitted to an existing theoretical model for temporal variation in fitness it is shown that varying herbivore pressure by T. jacobaeae in interaction with ants defending aphid-infested plants with a low pyrrolizidine alkaloid concentration can lead to a stable polymorphism in pyrrolizidine alkaloid concentration. Costs of the production and maintenance of pyrrolizidine alkaloids are not accounted for in the model. [ABSTRACT FROM AUTHOR]

We hypothesized that due to the absence of specialist herbivores in introduced ranges, invasive plants have evolved decreased allocation to carbohydrate storage for regrowth ability and as a consequence allocate more to growth. In this study, we compared plant growth, carbohydrate storage and regrowth ability of invasive and native Jacobaea vulgaris in response to complete shoot defoliation. We used invasive J. vulgaris genotypes from three geographically and climactically distinct regions and compared these with native genotypes from Europe. We found that invasive genotypes initially grew larger while native genotypes regrew larger after defoliation. Before defoliation, the carbohydrate storage in roots of invasive genotypes was 38% lower than native genotypes. Biomass after regrowth increased with root carbohydrate storage while it decreased with structural root mass, showing that it is crucial to study root storage and structural components separately in order to investigate plant regrowth. All studied traits of invasive populations from the three geographically and climatologically distinct regions changed in the same expected direction suggesting that the shifts in herbivore guild were causal to the observed change in growth and regrowth ability rather than environmental factors. [ABSTRACT FROM AUTHOR]