Herbivore‐induced plant responses in Brassica oleracea prevail over effects of constitutive resistance and result in enhanced herbivore attack

1. Plant responses to herbivore attack may have community‐wide effects on the composition of the plant‐associated insect community. Thereby, plant responses to an early‐season herbivore may have profound consequences for the amount and type of future attack. 2. Here we studied the effect of early‐season herbivory by caterpillars of Pieris rapae on the composition of the insect herbivore community on domesticated Brassica oleracea plants. We compared the effect of herbivory on two cultivars that differ in the degree of susceptibility to herbivores to analyse whether induced plant responses supersede differences caused by constitutive resistance. 3. Early‐season herbivory affected the herbivore community, having contrasting effects on different herbivore species, while these effects were similar on the two cultivars. Generalist insect herbivores avoided plants that had been induced, whereas these plants were colonised preferentially by specialist herbivores belonging to both leaf‐chewing and sap‐sucking guilds. 4. Our results show that community‐wide effects of early‐season herbivory may prevail over effects of constitutive plant resistance. Induced responses triggered by prior herbivory may lead to an increase in susceptibility to the dominant specialists in the herbivorous insect community. The outcome of the balance between contrasting responses of herbivorous community members to induced plants therefore determines whether induced plant responses result in enhanced plant resistance.     

Future directions in the ontogeny of plant defence: understanding the evolutionary causes and consequences

Plant defence often varies by orders of magnitude as plants develop from the seedling to juvenile to mature and senescent stages. Ontogenetic trajectories can involve switches among defence traits, leading to complex shifting phenotypes across plant lifetimes. While considerable research has characterised ontogenetic trajectories for now hundreds of plant species, we still lack a clear understanding of the molecular, ecological and evolutionary factors driving these patterns. In this study, we identify several non‐mutually exclusive factors that may have led to the evolution of ontogenetic trajectories in plant defence, including developmental constraints, resource allocation costs, multi‐functionality of defence traits, and herbivore selection pressure. Evidence from recent physiological studies is highlighted to shed light on the underlying molecular mechanisms involved in the regulation and activation of these developmental changes. Overall, our goal is to promote new research avenues that would provide evidence for the factors that have promoted the evolution of this complex lifetime phenotype. Future research focusing on the questions and approaches identified here will advance the field and shed light on why defence traits shift so dramatically across plant ontogeny, a widespread but poorly understood ecological pattern.     

Identification by 2-D DIGE of apoplastic proteins regulated by oligogalacturonides in Arabidopsis thaliana

Oligogalacturonides (OGs) are elicitors of plant defence responses released from the homogalacturonan of the plant cell wall during the attack by pathogenic micro-organisms. The signalling pathway mediated by OGs remains poorly understood, and no proteins involved in their signal perception and transduction have yet been identified. In order to shed light into the molecular pathways regulated by OGs, a differential proteomic analysis has been carried out in Arabidopsis. Proteins from the apoplastic compartment were isolated and their expression compared between control and OG-treated seedlings. 2-D gels and difference in gel electrophoresis (DIGE) techniques were used to compare control and treated proteomes in the same gel. The analysis of subcellular proteomes from seedlings allowed the identification of novel and low abundance proteins that otherwise remain masked when total cellular extracts are investigated. The DIGE technique showed to be a powerful tool to overcome the high interexperiment variation of 2-D gels. Differentially expressed apoplastic proteins were identified by MS and included proteins putatively involved in recognition as well as proteins whose PTMs are regulated by OGs. Our findings underscore the importance of cell wall as a source of molecules playing a role in the perception of pathogens and provide candidate proteins involved in the response to OGs.     

Antioxidant-associated chemoprevention by sodium selenite in N-nitrosodiethylamine-induced and phenobarbital-promoted hepatocarcinogenesis in rats

The anticarcinogenic/antioxidant potential of sodium selenite (Se), a micronutrient, was evaluated on liver tumourigenesis induced by N-nitrosodiethylamine (DEN) and promoted by phenobarbital (PB; 0.05% in diet). Male, albino rats of the Wistar strain were exposed intravenously to a single dose of DEN (200 mg x kg(-1) body weight). Se (4 ppm in drinking water) was supplemented before initiation, or during initiation and/or during the promotion period of carcinogenesis. At the end of 16 weeks (after DEN administration) nodular incidence, the total number of nodules and non-enzymic antioxidants such as vitamin E, vitamin C, total thiol, protein thiol and non-protein thiol contents were measured in hepatoma, surrounding tissue and kidney tissue of control and experimental groups. In hepatoma-bearing animals the above biochemical changes were decreased when compared with normal control animals. On Se treatment throughout the study, (20 weeks) the above biochemical changes reverted to normal levels. Pre- and post-treatment with Se also shows a tendency to reverse the above changes. The results indicate that prior application of Se significantly reverses the adverse changes produced during the tumourigenesis. Furthermore, prior applications of Se significantly reduced the cumulative number of tumours per tumour-bearing animals. The present study reveals the antitumour potential of Se against DEN-induced liver carcinogenesis.     

Invasive plant population and herbivore identity affect latex induction

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Conifer responses to a stylet‐feeding invasive herbivore and induction with methyl jasmonate: impact on the expression of induced defences and a native folivore

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Ontogenetic shifts in resource allocation: colour change and allometric growth of defensive and reproductive structures in the Caribbean spiny lobster Panulirus argus

Resource allocation theory predicts a disproportionately large allocation of resources to defensive structures during early ontogeny in organisms that are subject to more intense predation at smaller than at larger body sizes. We tested this prediction on the Caribbean spiny lobster Panulirus argus, which exhibits a negative relationship between predation risk and body size with a high natural mortality of smaller individuals. Independent allometric growth analyses demonstrated that numerous defensive structures (e.g. orbital horns, segments supporting the antenna, the tail fan) display negative allometric growth throughout ontogeny. We interpret these findings as lobsters investing disproportionately more resources to defensive structures when small to improve survivorship. Similarly, we observed an ontogenetic shift in lobster colour pattern; small individuals (< 23 mm carapace length) that inhabit nursery grounds (preferably among red algae) displayed a disruptive pattern (camouflage), whereas larger juveniles displayed a bicolour pigmentation typical of adult lobsters. This shift in colour pattern further suggests that small lobsters employ cryptic coloration throughout their asocial algal stage. However, this cryptic coloration offers no advantage when lobsters grow larger and start dwelling in crevices. Other structures linked to reproduction (e.g. female pleopods and male pereopods) experienced either isometric or positive allometric growth throughout ontogeny. Our results support one of the main predictions of resource allocation theory and demonstrate ontogenetic shifts in defensive structures and coloration concomitantly with changes in lobster mortality risk mediated by size‐dependent predation risk. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ●● , ●●–●●.     

Effects of plant quality and ant defence on herbivory rates in a neotropical ant‐plant

1. Understanding the degree to which populations and communities are limited by both bottom‐up and top‐down effects is still a major challenge for ecologists, and manipulation of plant quality, for example, can alter herbivory rates in plants. In addition, biotic defence by ants can directly influence the populations of herbivores, as demonstrated by increased rates of herbivory or increased herbivore density after ant exclusion. The aim of this study was to evaluate bottom‐up and top‐down effects on herbivory rates in a mutualistic ant‐plant. 2. In this study, the role of Azteca alfari ants as biotic defence in individuals of Cecropia pachystachya was investigated experimentally with a simultaneous manipulation of both bottom‐up (fertilisation) and top‐down (ant exclusion) factors. Four treatments were used in a fully factorial design, with 15 replicates for each treatment: (i) control plants, without manipulation; (ii) fertilised plants, ants not manipulated; (iii) unfertilised plants and excluded ants and (iv) fertilised plants and ants excluded. 3. Fertilisation increased the availability of foliar nitrogen in C. pachystachya, and herbivory rates by chewing insects were significantly higher in fertilised plants with ants excluded. 4. Herbivory, however, was more influenced by bottom‐up effects – such as the quality of the host plant – than by top‐down effects caused by ants as biotic defences, reinforcing the crucial role of leaf nutritional quality for herbivory levels experienced by plants. Conditionality in ant defence under increased nutritional quality of leaves through fertilisation might explain increased levels of herbivory in plants with higher leaf nitrogen.     

Systemic Acquired Resistance of Pepper to Microbial Pathogens

To cope with the challenge of pathogens, plants have evolved a wide variety of resistance mechanisms that rely both on constitutive and on inducible defences. Systemic acquired resistance (SAR), a form of inducible resistance that occurs following an earlier localized exposure to a pathogen, provides a long‐lasting systemic immunity against a wide range of pathogens in plants. The great benefits of SAR lead to its practical use in agriculture for plant disease management. Pepper (Capsicum annuum) is one of the economically important crops growing worldwide, and in this review, we summarize the scientific research‐based studies of SAR in pepper during the past decades. Effects of various exogenous inducers of SAR, such as salicylic acid, DL‐β‐amino‐n‐butyric acid, benzothiadiazols and avirulent pathogens on pepper plants have been extensively investigated by different research groups. Biochemical and molecular studies of SAR phenomena also revealed the involvement of radical burst, cell death, endogenous hormonal signalling and defence‐related gene expression during SAR establishment in pepper. New knowledge and understanding emerging from the pepper SAR studies will allow the development of novel approaches to enhance the durable resistance of pepper to pathogens, thereby helping to secure the future supply of safe and nutritious pepper worldwide.     

Glutamate Fermentation By‐product Activates Plant Defence Responses and Confers Resistance Against Pathogen Infection

In the food industry, glutamate fermentation by‐product (GFB) is generated by purifying glutamate products from microbial fermentation. The potential applications of GFB for upgrading agricultural soil, for foliar fertility, and as plant plankton for shrimp have been studied. We examined the efficacy of GFB foliar application and determined that GFB treatment increased the resistance of Arabidopsis leaves to infection by bacterial pathogens. Microarray gene expression analysis of Arabidopsis leaves after treatment with GFB indicated that the expression of plant defence‐related genes increased. In Corynebacterium fermentation, the active substances for induction of the defence response were extracted or solubilized after treatment with heating under acidic conditions. This extract was also effective in strawberry and grape leaves for the induction of hydrogen peroxide production. These findings suggest that foliar application of GFB that contains elicitor molecules derived from fermentation bacteria is useful for plant protection in agricultural fields.     

Are behavioural responses to predation cues linked across life cycle stages?

1. Prey organisms can perceive cues to predation hazard and adopt low‐risk behaviours to increase survival. Animals with complex life cycles, such as insects, can exhibit such anti‐predatory behaviours in multiple life stages. 2. Cues to predation risk may induce ovipositing females to choose habitats with low predation risk. Cues to predation risk may also induce larvae to adopt facultative behaviours that reduce risk of predation. 3. One hypothesis postulates that anti‐predation behaviours across adult and larval stages may be negatively associated because selection for effective anti‐predator behaviour in one stage leads to reduced selection for avoidance of predators in other stages. An alternative hypothesis suggests that selection by predation favours multi‐component defences, with both avoidance of oviposition and facultative adoption of low‐risk behaviours by larvae. 4. Laboratory and field experiments were used to determine whether defensive responses of adult and larval mosquitoes are positively or negatively associated. The study tested effects of waterborne cues from predatory Toxorhynchites theobaldi on oviposition choices and larval behaviours of three of its common prey: Culex mollis, Limatus durhamii and Aedes albopictus. 5. Culex mollis shows strong anti‐predator responses in both life stages, consistent with the hypothesis of a multi‐component behavioural defence. The other two species showed no detectable responses to waterborne predator cues in either adult or larval stages. Larvae of these unresponsive species were significantly more vulnerable to this predator than was C. mollis. 6. For these mosquitoes, species appear either to have been selected for multi‐component defences against predation or to act in ways that could be called predator‐naïve.     

Nesting Success in Crimson Finches: Chance or Choice?

In avian systems, nest predation is one of the most significant influences on reproductive success. Selection for mechanisms and behaviours to minimise predation rates should be favoured. To avoid predation, breeding birds can often deter predators through active nest defence or by modifying behaviours around the nest (e.g. reducing feeding rates and vocalisations). Birds might also benefit from concealing nests or placing them in inaccessible locations. The relative importance of these strategies (behaviour vs. site selection) can be difficult to disentangle and may differ according to life history. Tropical birds are thought to experience higher rates of predation than temperate birds and invest less energy in nest defence. We monitored a population of crimson finches (Neochmia phaeton), in the Australian tropics, over two breeding seasons. We found no relationship between adult nest defence behaviour (towards a model reptile predator) and the likelihood of nest success. However, nest success was strongly related to the visibility of the nest and the structure of the vegetation. We found no evidence that adult nest building decisions were influenced by predation risk; individuals that re‐nested after a predation event did not build their nest in a more concealed location. Therefore, predator avoidance, and hence nest success, appears to be largely due to chance rather than due to the behaviour of the birds or their choice of nesting sites. To escape high predation pressures, multiple nesting attempts both within and between seasons may be necessary to increase reproductive success. Alternatively, birds may be limited in their nest‐site options; that is, high‐quality individuals dominate quality nest sites.     

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.     

Benefits of parental care: Do juvenile lizards obtain better‐quality habitat by remaining with their parents?

Abstract Evolutionary theory suggests that parental care is favoured by natural selection when the benefits to offspring fitness outweigh the costs of parental expenditure. The nature of such benefits may differ among species, however, especially in species reflecting independent evolutionary origins of parental care. Black rock skinks (Egernia saxatilis, Scincidae) of south‐eastern Australia are viviparous rock‐dwelling lizards with prolonged parent–offspring association; adult pairs vigorously defend their home range – and, when present, their offspring – against conspecifics. We addressed the hypothesis that, by remaining within their parents' (vigorously defended) home range, juveniles thereby obtain access to better‐quality habitats. Measurements of biologically significant variables (crevice size, sun exposure, vegetation cover) revealed little difference between shelter‐rocks used by solitary (‘orphan’) juveniles and those within family groups containing adults. Indeed, the only consistent differences involved larger (and therefore, less predator‐proof) crevices for juveniles within family groups than for solitary conspecifics. Our data thus falsify the hypothesis that parental care evolves because of benefits associated with habitat quality; instead, it appears that parental protection of juveniles against infanticidal conspecifics may be the most plausible benefit to parent–offspring association in this system.     

Antixenosis phloem‐based resistance to aphids: is it the rule?

1. The concept of plant defence syndrome states that plant species growing in similar biotic or abiotic constraints should have convergent defensive traits. This article is a first step to test the prediction of this concept, by conducting experiments on wild Solanum species (or accessions) that originated from the Andes. The nature and the tissue localisation of the resistance of five wild Solanum species known to be resistant against the aphids Myzus persicae and Macrosiphum euphorbiae were determined by olfactometry and electrical penetration graph experiments. 2. Volatile organic compounds may contribute to wild Solanum resistance, depending on Solanum accessions and aphid species. Volatiles of S. bukasovii and S. stoloniferum PI 275248 were not attractive to M. persicae, whereas S. bukasovii was repulsive to M. euphorbiae. In contrast, volatiles of S. stoloniferum PI 275248 were attractive for M. euphorbiae. 3. Some wild Solanum species presented a generalised resistance in all plant tissues, so as for S. bukasovii and S. stoloniferum PI 275248 against M. persicae. However, except for S. bukasovii which was susceptible to M. euphorbiae, all tested Solanum species presented a phloem‐based antixenosis resistance against the two aphid species. 4. A review of articles focused on the nature of resistance of wild Solanum species against aphids corroborated with our results, i.e. a phloem‐based antixenosis resistance against aphids is the rule concerning the system aphids–wild Solanum species.     

Costs, benefits and the evolution of inducible defences: a case study with Daphnia pulex

Phenotypic plasticity is one major source of variation in natural populations. Inducible defences, which can be considered threshold traits, are a form of plasticity that generates ecological and evolutionary consequences. A simple cost-benefit model underpins the maintenance and evolution of these threshold, inducible traits. In this model, a rank-order switch in expected fitness, defined by costs and benefits of induction between defended and undefended morphs, predicts the risk level at which individuals should induce defences. Here, taking predator-induced morphological defences in Daphnia pulex as a threshold trait, we provide the first comprehensive investigation into the costs and benefits of a threshold trait, and how they combine to reflect fitness and predict the switchpoint at which induction should occur. We develop reaction norms that show genetic variation in switchpoints. Further experiments show that induction can confer a survival benefit and a cost in terms of lifetime reproductive success. Together, these two traits combine to estimate expected fitness and can predict the switchpoint between an undefended and a defended strategy. The predictions match the reaction norm data for clones that experience these costs and benefits, and correspond well to independent field data on induction. However, predictions do not, and cannot, match for clones that do not gain a benefit from induction. This study confirms that a simple theory, based on life history costs and benefits, is a sufficient framework for understanding the ecology and evolution of inducible, threshold traits.     

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.     

Visual cues contribute to predator detection in anuran larvae

The ability of prey to detect predators directly affects their probability of survival. Chemical cues are known to be important for predator detection in aquatic environments, but the role of other potential cues is controversial. We tested for changes in behaviour of Rana temporaria tadpoles in response to chemical, visual, acoustic, and hydraulic cues originating from dragonfly larvae (Aeshna cyanea) and fish (Gasterosteus aculeatus). The greatest reduction in tadpole activity occurred when all cues were available, but activity was also significantly reduced by visual cues only. We did not find evidence for tadpoles lowering their activity in response to acoustic and hydraulic cues. There was no spatial avoidance of predators in our small experimental containers. The results show that anuran larvae indeed use vision for predator detection, while acoustic and hydraulic cues may be less important. Future studies of predator‐induced responses of tadpoles should not only concentrate on chemical cues but also consider visual stimuli. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ??, ??–??.     

Trade‐offs between life‐history traits at range‐edge and central locations

The allocation of resources to different life‐history traits should represent the best compromise in fitness investment for organisms in their local environment. When resources are limiting, the investment in a specific trait must carry a cost that is expressed in trade‐offs with other traits. In this study, the relative investment in the fitness‐related traits, growth, reproduction and defence were compared at central and range‐edge locations, using the seaweed Ascophyllum nodosum as a model system. Individual growth rates were similar at both sites, whereas edge populations showed a higher relative investment in reproduction (demonstrated by a higher reproductive allocation and extended reproductive periods) when compared to central populations that invested more in defence. These results show the capability of A. nodosum to differentially allocate resources for different traits under different habitat conditions, suggesting that reproduction and defence have different fitness values under the specific living conditions experienced at edge and central locations. However, ongoing climate change may threaten edge populations by increasing the selective pressure on specific traits, forcing these populations to lower the investment in other traits that are also potentially important for population fitness.