Invasive plant population and herbivore identity affect latex induction

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Plant defence and stochastic risk of herbivory

Summary The influence of risk of herbivory and its variation in time on the optimal defence strategy in plants is analysed by a simple optimization model. We contrast two possible defence strategies; a constitutive defence with an invariant defence level in time and an idealized induced defence, that is, a strategy that adjusts the defence level to the prevailing risk of herbivory. We also take into account effects of the efficiency of the defence. If there is no variation in risk of herbivory over years, constitutive and induced defence should have the same expected optimal defence level and both strategies are equally fit. The optimal defence level increases as the maximum fecundity and the adult to juvenile survival ratio of the plants both increase. If the risk of herbivory varies stochastically, the expected optimal level of the constitutive defence is either increased or unaffected by the variation, whereas the induced defence strategy may result in both higher or lower expected optimal defence levels as variance increases. This outcome is dependent on the mean risk of herbivory. It also depends on the defence efficiency, i.e. the shape (convex, concave or linear) of the defence function that relates the probability of survival if encountered by a herbivore to defence level. Thus, the defence level of plants interacting with variable herbivore populations cannot be unambiguously predicted unless the defence strategy (constitutive or induced), mean risk of herbivory, the form of the defence function and plant life history are known.     

The jasmonic acid-amino acid conjugates JA-Val and JA-Leu are involved in rice resistance to herbivores

The phytohormone jasmonic acid (JA) plays a core role in plant defence against herbivores. When attacked by herbivores, JA and its bioactive derivatives are accumulated at the damage site, and subsequently perceived by the jasmonate co-receptors COI1 and JAZ proteins. The (+)-7-iso-jasmonoyl-L-isoleucine (JA-Ile) is known to be the main active JA derivative controlling vascular plant responses to herbivores as well as other JA-regulated processes. However, whether other endogenous JA-amino acid conjugates (JA-AAs) are involved in herbivore-induced defence responses remain unknown. Here, we investigated the role of herbivore-elicited JA-AAs in the crop plant rice. The levels of five JA-AAs were significantly increased under the armyworm, leaf folder and brown planthopper attack. Of the elicited JA derivatives, JA-Ile, JA-Val and JA-Leu could serve as ligands to promote the interaction between rice COI1 and JAZs, inducing OsJAZ4 degradation in vivo. JA-Val or JA-Leu treatment increased the expression of JA- and defence-related pathway genes but not JA-Ile levels, suggesting that these JA-AAs may directly function in JA signalling. Furthermore, the application of JA-Val or JA-Leu resulted in JA-mediated plant growth inhibition, while enhancing plant resistance to herbivore attack. This study uncovers that JA-Val and JA-Leu also play a role in rice defence against herbivores.     

Comparative investigations into the feeding ecology of six Mantodea species

Summary Six mantid species (Sphodromantis viridis, Polyspilota aeruginosa, Hierodula unimaculata, Parasphendale agrionia, Mantis religiosa and Empusa pennata) were studied in laboratory feeding experiments. Mantids stalk their prey and pounce on it, grasping it with their forelegs. Only living prey is selected and it is consumed directly after the catch. The predator orients itself optically, and therefore only takes notice of moving prey. The maximum size of prey which mantids can overwhelm is species-specific and depends on the prey type. On average mantids eat crickets of 50% their own body-weight while cockroaches can weigh up to 110%. Feeding experiments with 101 species of potential prey of 21 invertebrate orders showed an average feeding rate of 70% and marked differences among the predators. Polyspilota proved to be the least specialized mantid and Empusa caught the smallest amount of prey. Most of the defence mechanisms which arthropods have developed against their enemies proved to be ineffective against mantids. Neither a hard chitinous exoskeleton nor poisonous substances prevented the mantids from attacking their prey successfully. The protective secretion of the cotton stainer Dysdercus intermedius proved to be effective at least in a few instances. Even though these bugs were killed, the mantids usually refused to eat the abdomen, where the glands that produce the protective secretion are to be found. Thanatosis, as exhibited by the chrysomelid Cassida viridis and by the phasmid Carausius morosus, proved to be the best protection against mantids.     

环境胁迫与生物防御反应

生物的生存总是逃避不了周围各种环境胁迫因素的影响。非生物因素如温度、水分、湿度、光照、营养、环境污染、物理干扰和土壤坚实度等;生物因素如有害生物的袭击等。兴衰存亡的关键,除了取决于胁迫的种类、强度     

Antioxidant associated chemoprevention by selenomethionine in murine tumor model

Effectiveness of selenium in different forms like sodium selenite, selenocysteine and selenomethionine has been compared in four different doses, namely 4, 6, 8 and 10 ppm of each, in terms of their bioavailability and prolongation of survival of Dalton's lymphorna (DL) bearing mice. Selenomethionine, at a dose of 8 ppm, was found to be the most bioavailable and least cytotoxic form that was capable of increasing the life span of the tumour bearing hosts maximally (almost two-fold). Benef iciality of selenomethionine has also been studied by observing continuous changes brought about by this compound on the glutathione (GSH) level, glutathione peroxidase (GPx) activity and extent of lipid peroxidation in the hepatic tissue of the tumour bearing hosts, which are indispensable for a cell to function normally and are found to exhibit significantly altered behaviour in neoplastic cells. Selenomethionine caused the maintenance of high steady state GSH level and a normal GPx activity during the fist phase of tumour growth. It also controlled lipid peroxidation during the first 15-20 days following tumour transplantation. These conditions helped in the maintenance of intracellular redox balance, cellular integrity and metabolic rhythms of cells in DL bearing mice receiving selenomethionine.Affiliation     

Plant-mediated effects in the Brassicaceae on the performance and behaviour of parasitoids

Direct and indirect plant defences are well studied, particularly in the Brassicaceae. Glucosinolates (GS) are secondary plant compounds characteristic in this plant family. They play an important role in defence against herbivores and pathogens. Insect herbivores that are specialists on brassicaceous plant species have evolved adaptations to excrete or detoxify GS. Other insect herbivores may even sequester GS and employ them as defence against their own antagonists, such as predators. Moreover, high levels of GS in the food plants of non-sequestering herbivores can negatively affect the growth and survival of their parasitoids. In addition to allelochemicals, plants produce volatile chemicals when damaged by herbivores. These herbivore induced plant volatiles (HIPV) have been demonstrated to play an important role in foraging behaviour of insect parasitoids. In addition, biosynthetic pathways involved in the production of HIPV are being unraveled using the model plant Arabidopsis thialiana. However, the majority of studies investigating the attractiveness of HIPV to parasitoids are based on experiments mainly using crop plant species in which defence traits may have changed through artificial selection. Field studies with both cultivated and wild crucifers, the latter in which defence traits are intact, are necessary to reveal the relative importance of direct and indirect plant defence strategies on parasitoid and plant fitness. Future research should also consider the potential conflict between direct and indirect plant defences when studying the evolution of plant defences against insect herbivory.     

Effects of light on direct and indirect defences against herbivores of young plants of Mallotus japonicus demonstrate a trade-off between two indirect defence traits

Background and Aims

Although most studies on plant defence strategies have focused on a particular defence trait, some plant species develop multiple defence traits. To clarify the effects of light on the development of multiple defence traits, the production of direct and indirect defence traits of young plants of Mallotus japonicus were examined experimentally under different light conditions.

Methods

The young plants were cultivated under three light conditions in the experimental field for 3 months from May to July. Numbers of ants and pearl bodies on leaves in July were examined. After cultivation, the plants were collected and the developments of trichomes and pellucid dots, and extrafloral nectaries (EFNs) on the leaves were examined. On plants without nectar-collecting insects, the size of EFNs and the volume of extrafloral nectar secreted from the EFNs were examined.

Key results

Densities of trichomes and pellucid dots did not differ significantly among the plants under the different light conditions, suggesting that the chemical and physical defences function under both high and low light availability. The number of EFNs on the leaves did not differ significantly among the plants under the different light conditions, but there appeared to be a trade-off between the size of EFNs and the number of pearl bodies; the largest EFNs and the smallest number of pearl bodies were found under high light availability. EFN size was significantly correlated with the volume of extrafloral nectar secreted for 24 h. The number of ants on the plants was smaller under low light availability than under high and moderate light availability.

Conclusions

These results suggest that direct defence traits function regardless of light conditions, but light conditions affected the development of indirect defence traits.     

Meadow pipit (Anthus pratensis) egg appearance in cuckoo (Cuculus canorus) sympatric and allopatric populations

Host populations tend to show less ability to discriminate against parasites when living in their absence. However, comparison of rejection rates among sympatric and allopatric host populations does not allow determination of whether the greater tolerance in allopatric populations reflects a genetic change or phenotypic plasticity. Here we test the existence of changes in a host's adaptation to brood parasitism in the absence of parasitism by studying intraclutch variation in egg appearance, which is a genetically determined component of host defence favouring discrimination of parasitic eggs. We investigated egg phenotypes of a common host of the European cuckoo, Cuculus canorus , in the presence and in the absence of cuckoos. By using objective spectroradiometry techniques of colour assessment we compared intraclutch variation between populations of meadow pipit, Anthus pratensis , sympatric (England) and allopatric (Iceland and Faeroe Islands) with C. canorus . Allopatric populations of A. pratensis showed greater intraclutch variation in egg appearance in the ultraviolet part of the spectrum than did a population sympatric with C. canorus . Two possible alternative mechanisms explaining these findings are discussed.  © 2003 The Linnean Society of London, Biological Journal of the Linnean Society , 2003, 79 , 543–549.     

Parental risk management in relation to offspring defence: bad news for kids

Do parents defend their offspring whenever necessary, and do self-sacrificing parents really exist? Studies recognized that parent defence is dynamic, mainly depending on the threat predators pose. In this context, parental risk management should consider the threat to themselves and to their offspring. Consequently, the observed defence should be a composite of both risk components. Surprisingly, no study so far has determined the influence of these two threat components on parental decision rules. In a field experiment, we investigated parental risk taking in relation to the threat posed to themselves and their offspring. To disentangle the two threat components, we examined defence behaviours of parent blue tits Cyanistes caeruleus towards three different predators and during different nestling developmental stages. Nest defence strategies in terms of alarm call intensity and nearest predator approach differed between the three predators. Defence intensity was only partly explained by threat level. Most importantly, parental risk management varied in relation to their own, but not offspring risk. Parent defence investment was independent of nestling risk when parents followed a high-risk strategy. However, parents considered nestling as well as parental risk when following a low-risk strategy. Our findings could have general implications for the economy of risk management and decision-making strategies in living beings, including humans.     

Trade-offs in non-native plant herbivore defences enhance performance

Non-native plants are typically released from specialist enemies but continue to be attacked by generalists, albeit at lower intensities. This reduced herbivory may lead to less investment in constitutive defences and greater investment in induced defences, potentially reducing defence costs. We compared herbivory on 27 non-native and 59 native species in the field and conducted bioassays and chemical analyses on 12 pairs of non-native and native congeners. Non-natives suffered less damage and had weaker constitutive defences, but stronger induced defences than natives. For non-natives, the strength of constitutive defences was correlated with the intensity of herbivory experienced, whereas induced defences showed the reverse. Investment in induced defences correlated positively with growth, suggesting a novel mechanism for the evolution of increased competitive ability. To our knowledge, these are the first linkages reported among trade-offs in plant defences related to the intensity of herbivory, allocation to constitutive versus induced defences, and growth.     

Leaf chemistry of woody plants in relation to season,canopy retention and goat browsing in a semiarid subtropical savanna

Abstract It is assumed that the phytochemistry of browse species protects their biomass and nutrients against herbivory. In this study we were primarily interested in (i) seasonal and phenology‐related variations in leaf chemistry, and (ii) chemistry‐related variations in the feeding behaviour of domestic goats. Such knowledge would guide management‐orientated modelling of browse–browser interactions in seasonal, subtropical zones where goats are abundant. The browse species studied were typical of semiarid savannas in southern Africa: Grewia occidentalis L. (Tiliaceae), Scutia myrtina (Burm. f) Kurz (Rhamnaceae), Diospyros lycioides Desf. ssp. lycioides (Ebenaceae), Rhus longispina Eckl. and Zeyh. (Anacardiaceae), Ehretia rigida (Thunb.) Druce (Boraginaceae) and Acacia karroo Hayne (Mimosoideae). Nitrogen (N), phosphorus (P), condensed tannins (CT), protein‐precipitating tannins (PPT), total phenols (TP), cellulose and lignin concentrations were estimated for each species during the late dormant and early growing seasons. N, P, CT and TP were elevated during the growth season, while cellulose, lignin and PPT decreased. Unlike cytoplasm contents, which varied seasonally, cell wall and vacuole contents varied both seasonally and among species. Except that seasonal variation in N of deciduous species was greater than that of evergreen species, leaf phenology was not related to variations in forage quality. Short‐term intake rates were not related to primary metabolite concentrations, but were positively related to secondary metabolites. Elevated intake rates of putative defences were concluded to be side‐effects of attempts by goats to increase nutrient intake rate, indicating tolerance of chemical defences. Without support for the hypothesis that chemical defences are correlated to canopy retention, we propose an alternative hypothesis, that defences are distributed among woody plants in semiarid, subtropical savannas according to shoot morphology because it affects the vulnerability of plant parts to browsers.     

Operculum closing as a defence against predatory leeches in four British freshwater prosobranch snails

The defence reaction of operculum closing in response to the presence of the molluscivorous leech Glossiphonia complanata (L.) and the non-molluscivorous Erpobdella octoculata (L.) was studied in four species of freshwater prosobranch gastropod. Bithynia tentaculata (L.) and Valvata piscinalis (Müller) can distinguish between the leeches, reacting only to G. complanata. V. piscinalis is capable of a greater degree of distance chemoreception of the leech ‘scent’. Valvata cristata Müller and Potamopyrgus jenkinsi (Smith) did not react to either leech. V. cristata may not be a potential prey item for G. complanata, while P. jenkinsi is fed on by the leech, but is a relative newcomer to the freshwater fauna. Animal Ecology Research Group, Department of Zoology, University of Oxford Commonwealth Forestry Institute, Department of Plant Sciences, University of Oxford     

The consequences of leaf damage for subsequent insect grazing on birch (Betula spp.)

Summary Low levels of artificial damage were imposed on the leaves of Betla pubescens and B. pendula in early summer 1985. Sixteen tress were used and the damage was distributed throughout the canopy in two ways. It was either randomly dispersed on the tree, or restricted to a localised region of the canopy. Up to 250 leaves/tree were damaged and the position of control leaves was marked as appropriate. At the end of the summer the experimental and control leaves were collected for analysis. Subsequent patterns of grazing by naturally-occurring herbivores were affected by the previous damage to the foliage. Fewer artificially-damaged leaves received subsequent insect grazing damage. The frequecy distribution of insect damage to previously-damaged leaves was significantly different from that of the control leaves, and less leaf tissue was removed from those experimental leaves which did receive subsequent insect attack. The evidence presented suggests that wound-induced changes in leaf palatability do occur in B. pubescens and B. pendula in the field and that a major role is to disperse the damage throughout the canopy.     

Leaf thionins, a novel class of putative defence factors

Leaf thionins of barley have been identified as a novel class of highly abundant polypeptides with antifungal activity, which are present in walls and vacuoles of barley leaf cells. Similar thionins occur not only in monocotyledonous but also in various dicotyledonous plants. The leaf thionins of barley are encoded by a complex multigene family, which consists of at least 50–100 members per haploid genome. The toxicity of these thionins for plant pathogenic fungi and the fact that their synthesis can also be triggered by pathogens strongly suggest that leaf thionins are involved in the mechanism of plant defence against microbiol infection.