Efficacy Of Defenses Research Articles

Interspecific variation in the defensive responses of obligate plant-ants: experimental tests and consequences for herbivory.

The aggressive behavior of ants that protect plants from herbivores in exchange for rewards such as shelter or food is thought to be an important form of biotic defense against herbivory, particularly in tropical systems. To date, however, no one has compared the defensive responses of different ant taxa associated with the same plant species, and attempted to relate these differences to longer-term efficacy of ant defense. We used experimental cues associated with herbivory--physical damage and extracts of chemical volatiles from leaf tissue--to compare the aggressive responses of two ant species obligately associated with the Amazonian myrmecophyte Tococa bullifera (Melastomataceae). We also conducted a colony removal experiment to quantify the level of resistance from herbivores provided to plants by each ant species. Our experiments demonstrate that some cues eliciting a strong response from one ant species elicited no response by the other. For cues that do elicit responses, the magnitude of these responses can vary interspecifically. These patterns were consistent with the level of resistance provided from herbivores to plants. The colony removal experiment showed that both ant species defend plants from herbivores: however, herbivory was higher on plants colonized by the less aggressive ant species. Our results add to the growing body of literature indicating defensive ant responses are stimulated by cues associated with herbivory. However, they also suggest the local and regional variation in the composition of potential partner taxa could influence the ecology and evolution of defensive mutualisms in ways that have previously remained unexplored.

Preferential expression of a plant cystatin at nematode feeding sites confers resistance to Meloidogyne incognita and Globodera pallida

The expression patterns of three promoters preferentially active in the roots of Arabidopsis thaliana have been investigated in transgenic potato plants in response to plant parasitic nematode infection. Promoter regions from the three genes, TUB-1, ARSK1 and RPL16A were linked to the GUS reporter gene and histochemical staining was used to localize expression in potato roots in response to infection with both the potato cyst nematode, Globodera pallida and the root-knot nematode, Meloidogyne incognita. All three promoters directed GUS expression chiefly in root tissue and were strongly up-regulated in the galls induced by feeding M. incognita. Less activity was associated with the syncytial feeding cells of the cyst nematode, although the ARSK1 promoter was highly active in the syncytia of G. pallida infecting soil grown plants. Transgenic potato lines that expressed the cystatin OcIDeltaD86 under the control of the three promoters were evaluated for resistance against Globodera sp. in a field trial and against M. incognita in containment. Resistance to Globodera of 70 +/- 4% was achieved with the best line using the ARSK1 promoter with no associated yield penalty. The highest level of partial resistance achieved against M. incognita was 67 +/- 9% using the TUB-1 promoter. In both cases this was comparable to the level of resistance achieved using the constitutive cauliflower mosaic virus 35S (CaMV35S) promoter. The results establish the potential for limiting transgene expression in crop plants whilst maintaining efficacy of the nematode defence.

Arms races between social parasites and their hosts: geographic patterns of manipulation and resistance

The evolutionary interactions between permanently social parasitic species and their hosts are of special interest because social parasites are not only closely dependent on, but are also closely related to, their hosts. The small European slavemaker Harpagoxenus sublaevis has evolved several characters that help manipulate its host. In this study we investigated adaptations of this social parasite to its local hosts and the geographic pattern of host resistance in two main host species from three different populations. In behavioral experiments, we examined whether host colonies from three geographically distant Leptothorax acervorum populations varied in their ability to defend the nest against social parasites. Naive colonies from the unparasitized English population killed attacking slavemakers more often than did host colonies from two parasitized populations. We also found strong interpopulation variation in the ability of the slavemaker to manipulate host behavior. H. sublaevis uses the Dufour gland secretion to induce intracolonial fights and, in general, this propaganda substance was most effective against local hosts. Our results suggest that the social parasite is leading the arms race in this aspect. Similar experiments uncovered differences between two populations of the second host species L. muscorum and could demonstrate that nest defense in both host species is similarly efficient. In L. acervorum, monogynous colonies were more successful in nest defense, whereas social structure had no impact in L. muscorum. Colony size did not affect the efficacy of nest defense in either host species. The caste of the slavemaker had a strong influence on the success of an attack. Copyright 2003.

Extraction and quantification of "condensed tannins" as a measure of plant anti-herbivore defence? Revisiting an old problem.

Contents of phenolic compounds in leaf extracts often serve as a measure of plant anti-herbivore defence. This method suffers from the multifunctionality of phenolics and from problems with their colorimetric quantification. Here we present further evidence for the pertinence of these problems. Contents of condensed tannins (CCT) were spectrophotometrically quantified in leaf extracts of 11 closely related mimosoid species, and Spodoptera littoralis caterpillars were reared on artificial diet containing these extracts. The relationship of CCT with caterpillar growth differed considerably among plant species, since both positive and negative correlations were detected. There was, however, a negative correlation of CCT with fungal spore germination, indicating a role of these compounds in resistance to fungi. Detailed knowledge on the structure and biological function of defensive compounds and on the overall composition of leaves is required to estimate a plant's defensive efficacy against a particular group of enemies.

Nutrient allocation of Macaranga triloba ant plants to growth, photosynthesis and indirect defence

Summary 1. Allocation patterns are an important aspect of plant life strategies. In particular, many hypotheses on plant antiherbivore defence – such as the growth differentiation balance hypothesis and the resource availability hypothesis – concern constraints on resource allocation to defence, and assume defence to be limited by nutrient supply under most, yet not all, conditions. 2. Field‐grown Macaranga triloba saplings were fertilized, and temporal and spatial patterns in the response of growth, photosynthesis and investment in biotic defence against herbivores and pathogens were measured simultaneously. Macaranga triloba produces food bodies to nourish mutualistic ants which protect their hosts against herbivores and pathogens. Food body production rate is quantitatively related to ant colony structure, and the latter is correlated with defensive efficacy. Food body production can therefore serve as a measure of the plant's investment in defence. 3. Food body production responded quickly, and on all food body‐producing stipules, to increased nutrient supply. In contrast, photosynthetic capacity responded much more slowly, to a smaller degree, and only in leaves that emerged after the onset of fertilization. No significant effects on plant growth were seen. 4. Our results show that food body production by M. triloba is regulated directly by nutrient availability. There was no evidence that increased nutrient supply was preferably allocated to growth and/or photosynthesis, which forms a central assumption of most hypotheses on plant antiherbivore defence. 5. Phenotypic plasticity and the ability to make use of short pulses in nutrient supply are of particular importance in pioneer plants inhabiting rapidly changing habitats. New theoretical frameworks are required for the inclusion of phenotypically plastic defence traits in the theory of plant antiherbivore defence.

Effects of the peptide mycotoxin destruxin E on insect haemocytes and on dynamics and efficiency of the multicellular immune reaction.

Destruxins (DTXs) are cyclic peptide toxins secreted by the entomopathogenic fungus Metarhizium anisopliae var. anisopliae. The effects of DTX E, the most active compound of this family on haemocytes, the immunocompetent insect cells, and on the dynamics and efficacy of the multicellular defense of insect hosts have been investigated. Ultrastructural alterations have been observed in circulating plasmatocytes and granular haemocytes, and in attached haemocytes of Galleria mellonella larvae treated with a toxic dose of DTX E (LC50). These changes appear as a consequence of disturbances induced in the cellular calcium balance. An effect on the cell surface of granulocytes was also noted in cells incubated with the toxin and FITC-Con A, even when the concentration of DTX was as low as 0.005 microg/ml. Morphological studies of haemocytic capsules formed in vivo revealed disturbances of the multicellular defense mechanism after toxin treatment However, an attempt to establish if these changes were significant was unsuccessful. In contrast, comparative assays regarding the effect of toxin treatment on the efficacy of the antifungal effect of encapsulation has given conclusive results. The germination of injected Aspergillus niger spores became slightly but significantly increased, and when the granuloma were incubated the fungus escaped more easily from the haemocytic envelope. These results are discussed in terms of significance of the contribution of DTXs to the fungal infection process. It is suggested that the fungal peptides may intervene during the disease by a true immune-inhibitory effect occurring at doses which do not cause paralysis or any general sign of toxicity (e.g., 0.8 microg/g of body weight).

Are House Wren Troglodytes aedon eggs unusually strong? Test of the predicted effect of intraspecific egg destruction

As a result of opposing selective forces, the external strength of avian eggs should be near some size‐specific optimum. However, in certain situations there should be selection on females to lay unusually strong eggs. According to one hypothesis, intraspecific egg destruction should favour increased egg strength as a means of defence against conspecific intruders. This hypothesis predicts that House Wrens Troglodytes aedon, a species well known for its tendency to destroy conspecific clutches, should be under selection for unusually strong eggs. However, the intensity of selection for strong eggs should also be modified by efficacy of nest defence against conspecific intruders in a given species (i.e. efficient nest defence by the breeding pair should weaken selection for unusually strong eggs). The goals of our study were: (1) to establish whether House Wren eggs are stronger than expected for their size; (2) to determine which structural mechanisms are responsible for their unusual strength; and (3) to test a hypothesis that, between wren species, the efficacy of nest defence and the intensity of egg‐destroying behaviour affect the intensity of selection for unusually strong eggs. Our results demonstrated that: (1) House Wren eggs are 1.9 times stronger than expected for their size; (2) their unusual strength is achieved mostly by their unusually thick shells; and (3) eggs of the House Wren (extensive paternal nest defence; male egg‐destroying behaviour suppressed during incubation) are significantly weaker structurally than eggs of the Marsh Wren Cistothorus palustris (reduced paternal nest defence; male egg‐destroying behaviour present throughout incubation). These results are consistent with the hypothesis that the intraspecific egg‐destroying behaviour and the efficacy of nest defence by the breeding adults have played a role in the evolution of strength of House Wren eggs.

Property distribution and configurations of sovereign states: A rational economic model

A nation's wealth is both an object of conquest to covetous aggressors and a resource to its owners for self defense. To maintain autonomy every country must mount a defense which either makes its capture (1) more expensive than any aggressor can afford, or (2) more expensive than it is worth to aggressors. Whether this condition can be satisfied for all countries simultaneously depends as shown in this paper on relative efficacy of military offense versus defense, the aggregate of wealth among nations and its distribution, and the benefits a conqueror may obtain from conquest, including the duration of these benefits. The paper shows how these factors fit together to determine the sustainability and stability of the international distribution of property as embodied in the configuration of sovereign states.

Effects of elevated atmospheric carbon dioxide on insect–plant interactions

Effects of elevated atmospheric carbon dioxide on insect–plant interactions

On benefits of indirect defence: short- and long-term studies of antiherbivore protection via mutualistic ants.

Many plants are defended indirectly by mutualistic animals. In this field study, we investigated the efficacy of indirect antiherbivore defence in symbiotic and non-symbiotic ant-plant associations in three Macaranga species. We tested whether obligate interactions are more effective than facultative ones by comparing ant-free plants, or parts of plants, with untreated controls. All three species gained significant protection from the ants' presence. The efficacy of defence was higher in the obligate associations represented by M. triloba and M. hosei than in the facultative interaction (M. tanarius). After 40days of ant exclusion, missing leaf area amounted to 1.7% in M. hosei (compared to 0.2% in untreated, ant-defended controls), 2.6% in M. triloba (controls 1.2%) and 4.2% in M. tanarius (controls 3.2%). In a long-term study of M. triloba and M. hosei, ant protection was orders of magnitude higher than in the short-term results. Short-term experiments obviously are unsuited to obtaining a realistic picture of the long-term efficacy of antiherbivore defence. Within 1year, ant-free plants lost, on average, between 70% (M. hosei) and 80% (M. triloba) of their total leaf area. Both species appear to require their mutualistic ants for survival. Defence via symbiotic ants is obviously a very effective form of antiherbivore protection. Ants are highly mobile and defend preferentially young, vulnerable leaves and shoot tips, and they fulfil several functions which normally have to be provided by different chemical substances. This may be a general benefit of indirect plant defence, which makes use of "animal-specific" traits rather than intrinsic plant properties.

Nutrient availability and indirect (biotic) defence in a Malaysian ant-plant.

Tropical plants of different genera defend themselves via symbiotic ant colonies, which are housed and often nourished by their host plant. Many studies deal with the defensive effects of the ants, but none has linked the plants' investment in this type of defence to the size and defensive efficacy of the symbiotic ant colony. We show here that ant-food production by the obligate myrmecophyte, Macaranga triloba, is limited by nutrient supply. The colony size of the ants in untreated plants (which had not been affected by experiments in advance of colony collection and determination of food body production) was significantly correlated with the amount of food produced by their hosts, and the plants' level of leaf damage was significantly and negatively correlated with the number of inhabiting ant workers. Our study provides the first field data that show that nutrient availability can directly influence a myrmecophyte's investment in its ants. Further studies are needed to evaluate whether soil nutrient contents in general can be a factor that limits the ability of myrmecophytes to defend themselves indirectly by nourishing symbiotic ants.

Transformation of critical theory into apology in the work of Jurgen Habermas

In the paper is analyzed transformation of one part of 'critical theoreticians' into apologists and ideologists of the new old world capitalist order, within the context of twentieth century social conflicts. In the focus of attention is the article 'Bestiality and Humanism - A War on the Border between Law and Moral', that Habermas published during the 1999 NATO bombing of Yugoslavia and criminal violation of all valid national and international legal norms. It is demonstrated that Habermas' substitution of the critique of the gap between the preconditions for reasoned communication and real conditions of distorted communication, by moralizing justification of imperialist elimination of the gap between legality and supposed efficacy of the human rights' defense, conducted to the abandonment of critical theory's constitutive elements.

Oviposition Behavior ofAphelinus asychis(Hymenoptera: Aphelinidae) andAphidius matricariae(Hymenoptera: Aphidiidae) and Defense Behavior of Their HostDiuraphis noxia(Homoptera: Aphididae)

Laboratory experiments were done to determine whether differences in attack behavior of Aphelinus asychis Walker and Aphidius matricariae Haliday and defense by their host Diuraphis noxia (Mordvilko) could explain higher parasitism by A. asychis in the field. Attack behavior differed strongly between the 2 parasitoid species: A. asychis took 4 times longer to oviposit in individual hosts than A. matricariae, and A. matricariae parasitized 6 times more hosts per unit time. These differences may have arisen in part because A. asychis appears to assess host quality with its ovipositor after insertion and A. matricariae appears to assess host quality by antennal palpation before ovipositor insertion. Although adult A. asychis uses some hosts for nutrition rather than oviposition and A. matricariae does not, A. matricariae still killed more hosts per unit time than A. asychis. Although some D. noxia defended themselves when attacked, aphid defense did not reduce parasitism by either wasp species. Thus, neither difference in the efficacy of aphid defense nor difference in oviposition behavior can explain greater parasitism by A. asychis in the field.

Handguns, Violent Crime, and Self-Defense

By far the most plausible explanation of data on violent crime in the United States is that its high handgun ownership rate is a major causal factor. The only realistic way to significantly reduce violent crime in this country id an outright ban on private ownership of handguns. While such a ban would undeniably restrict one particular freedom, it would violate no rights. In particular, the unquestioned right to self-defense does not entail a right to own handguns, because the evidence indicates that the widespread belief in handguns' defensive efficacy is mistaken, especially when we confine our attention to defensive handgun use that is actually morally permissible. A handgun ban will never eradicate the weapons from this country, but it can substantially reduce violent crime. Although political realities may make a handgun ban unattainable in the United States at present, the very act of advancing cogent arguments for the most defensible position will make the goal of handgun prohibition more and more achievable

Inter-individual variation in sequestration (as measured by energy dispersive spectroscopy) predicts efficacy of defensive secretion in lubber grasshoppers

We tested whether inter-individual variation in concentration of sequestered compounds predicts defensive efficacy of the defensive secretion of onion-fed Eastern lubber grasshoppers. When fed onion, lubbers have the ability to sequester sulfur compounds into their defensive secretion, and the secretion from onion-fed lubbers is more deterrent of ants than the secretion from lubbers fed other diets (Jones et al. 1989). To test three hypotheses, we developed a method for measuring total sequestered sulfur in the secretion using energy dispersive spectroscopy (EDS). First, we found that lubbers fed an ad libitum, monophagous diet of onion produce more secretion and have higher concentrations of total sulfur in their secretions than lubbers fed other diets. These sulfur concentrations varied three-fold; we believe that this variation in the composition of defensive secretions stems from physiological variation. Second, our method was sensitive enough to detect sulfur in the secretion of some lubbers that had been fed onion only once. Third, the sulfur concentration of a secretion sample significantly predicted its ability to deter ants from foraging. Hence, our results suggest that inter-individual variation in defensive chemistry in insects offered the same diet may be ecologically important.

Chemistry and Defensive Efficacy of Secretion of Burrowing Bug (Sehirus cinctus cinctus)

Adult Sehirus cinctus cinctus emit a volatile secretion from their metathoracic scent glands when tactually stimulated. We identified the volatile components by gas chromatography, high-performance liquid chromatography, and mass spectrometry. The secretion of both sexes contained (1R)-(+)-α-pinene, (1S)-(–)-β-pinene, β-myrcene, (R)-(+)-limonene, and α-terpinolene. Two additional compounds were found in only female secretions: (E)-2-hexenyl acetate and (E)-2-octenal. We also tested the defensive capability of this insect by offering it to various predators. Anoles, starlings, and a killdeer rejected S. c. cinctus after an initial sampling. These findings suggest that the secretion plays a defensive role.

Floodplain development policy in England and Wales

There is evidence of substantial floodplain development in England and Wales. An ‘escalator effect’ is observed whereby progressively higher levels of flood defence are provided to protect against progressively increasing flood damage potential, caused mainly by post-defence development. The efficacy of current flood defence and floodplain planning policy is questioned. Planning influences floodplain development rather than prevents it. Wider planning constraints divert development towards floodplains to avoid other environmental problems. Floodplain development decisions should be taken in the context of the wider benefits of such development, as well as the natural and cultural functions of floodplains.

Host plant influence on chemical defense in conifer sawflies (Hymenoptera: Diprionidae).

Host diet affects the defensive efficacy of Neodiprion sawflies. In laboratory assays with wood ants (Formica obscuripes), secretions from larvae reared on Pinus banksiana were the most repellent, while those from P. resinosa feeders were the least so. This was explained diterpene resin acid content, but not total monoterpene content. The terpene content of regurgitant generally reflected dietary concentrations. Compounds were sequestered nonselectively by larvae. Host-based differences in defense persisted at the behavioral level. P. banksiana feeders regurgitated greater volumes of fluid and were less likely to be disabled or killed by ants in one-on-one interactions than were larvae fed on P. resinosa. The defensive advantages of host diet conflicted with developmental requirements. N. sertifer reared on P. banksiana (the best diet for defense in all cases) had lower cocoon weights (a correlate of fecundity) than those reared on other diets, and had prolonged larval development compared to insects fed P. sylvestris. No such tradeoff was detected in N. lecontei. Larvae of both species strongly preferred P. banksiana over P. resinosa in feeding choice assays.

Cytokine and growth factor regulation of macrophage scavenger receptor expression and function

Regulation of macrophage scavenger receptor (MSR) activity may be an important determinant of the extent of atherogenesis and the efficacy of host defense. The effect of M-CSF on this pathway was studied using a recently developed monoclonal antibody to murine MSR. M-CSF markedly and selectively increased MSR synthesis in murine macrophages (Mφ); post-translationally the receptor appeared more stable and shifted to a predominantly surface distribution. Functionally M-CSF enhanced modified lipoprotein uptake and increased divalent cation-independent adhesion in vitro. These results suggest a plausible mechanism whereby M-CSF production in the atheromatous plaque micro-environment could promote the recruitment and retention of mononuclear phagocytes and subsequent foam cell formation. In addition, the Th1 cytokine (γ-interferon) and Th2 cytokine (interleukin-4) had differential effects on MSR glycosylation in vitro suggesting a further possible regulatory role by these lymphokines on macrophage MSR function.

Plant Defenses and Optimal Foraging by Mammalian Herbivores

We examined, using an optimal-foraging model, the conditions under which particular plant defenses (e. g., structural, digestive-inhibiting chemicals, toxic chemicals, and nutritional content) should be effective in reducing intake of plants by mammalian herbivores. We demonstrated that no type of plant defense can guarantee reduced consumption, because defense efficacy depends not only upon other characteristics of the defended plant (e.g., its nutrient content, its passage rate through the herbivore's digestive tract, and its ability to be harvested by the herbivore), but also the characteristics of other plants available to the herbivore in the environment