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1,186 results for “defensiveness”
Data from: Chemical tradeoffs in seed dispersal: Defensive metabolites in fruits deter consumption by mutualist bats
Although fleshy fruits function primarily to attract seed dispersers, many animal-dispersed fruits contain potentially toxic secondary metabolites. These metabolites can provide defense against seed predators and pathogens, but their effects on dispersers are still poorly understood. In some cases plants may experience a tradeoff, where the metabolites that provide fruit defense also reduce seed disperser preferences. In other cases the bioactivity of fruit secondary metabolites may be directed primarily at pests with no negative effects on seed-dispersing vertebrates. We tested the effects of amides, a group of nitrogen-based defensive compounds common in the plant genus Piper (Piperaceae), in interactions with the primary seed dispersers of Piper in the neotropics – fruit-feeding bats in the genus Carollia (Phyllostomidae). In a series of flight cage experiments, pure amides and amide-rich fruit extracts reduced the preferences of bats for Piper fruit, affecting both the bats' initial choices to remove Piper infructescences and the proportion of fruit consumed from individual infructescences once they were removed. However, the effects of amides varied considerably among three species of Carollia and among the specific individual amides and extracts tested. Overall, our results support the hypothesis that plants experience a tradeoff between seed dispersal and fruit defense, but the strength of this tradeoff and the overall fitness consequences may depend strongly on ecological context.
Data from: The evolution of chemical defenses along invasion routes: Harmonia axyridis Pallas (Coccinellidae: Coleoptera) as a case study
The Evolution of Increased Competitive Ability (EICA) hypothesis (Blossey & Nötzold, 1995) postulates that escaping from coevolved enemies increases invaders fitness by energy reallocation from defenses and immunity to growth and reproduction. In this context, we evaluated the evidence of evolutionary change in invasive populations of Harmonia axyridis Pallas (Coccinellidae: Coleoptera). We measured egg defenses – cocktail of hydrocarbons on the egg's surface flagging egg toxicity, and the concentration of the main alkaloid harmonine - in individuals from three populations along the invasion route (Japan: native, USA: introduced more than 30 years ago, South Africa: introduced in the early 2000s) in a common garden experiment. Our results support the EICA hypothesis: we found changes along the invasion route in the profiles of the hydrocarbons coating the eggs' surface, and a decrease in the concentration of harmonine in eggs from the most recent invasive South African population compared to the long established in the USA and the native Japanese ones.
Data from: Are aphid parasitoids locally adapted to the prevalence of defensive symbionts in their hosts?
Background: Insect parasitoids are under strong selection to overcome their hosts' defences. In aphids, resistance to parasitoids is largely determined by the presence or absence of protective endosymbionts such as Hamiltonella defensa. Hence, parasitoids may become locally adapted to the prevalence of this endosymbiont in their host populations. To address this, we collected isofemale lines of the aphid parasitoid Lysiphlebus fabarum from 17 sites in Switzerland and France, at which we also estimated the frequency of infection with H. defensa as well as other bacterial endosymbionts in five important aphid host species. The parasitoids' ability to overcome H. defensa-mediated resistance was then quantified by estimating their parasitism success on a single aphid clone (Aphis fabae fabae) that was either uninfected or experimentally infected with one of three different isolates of H. defensa. Results: The five aphid species (Aphis fabae fabae, A. f. cirsiiacanthoides, A. hederae, A. ruborum, A. urticata) differed strongly in the relative frequencies of infection with different bacterial endosymbionts, but there was also geographic variation in symbiont prevalence. Specifically, the frequency of infection with H. defensa ranged from 22 to 47 % when averaged across species. Parasitoids from sites with a high prevalence of H. defensa tended to be more infective on aphids possessing H. defensa, but this relationship was not significant, thus providing no conclusive evidence that L. fabarum is locally adapted to the occurrence of H. defensa. On the other hand, we observed a strong interaction between parasitoid line and H. defensa isolate on parasitism success, indicative of a high specificity of symbiont-conferred resistance. Conclusions: This study is the first, to our knowledge, to test for local adaptation of parasitoids to the frequency of defensive symbionts in their hosts. While it yielded useful information on the occurrence of facultative endosymbionts in several important host species of L. fabarum, it provided no clear evidence that parasitoids from sites with a high prevalence of H. defensa are better able to overcome H. defensa-conferred resistance. The strong genetic specificity in their interaction suggests that it may be more important for parasitoids to adapt to the particular strains of H. defensa in their host populations than to the general prevalence of this symbiont, and it highlights the important role symbionts can play in mediating host-parasitoid coevolution.
Data from: Neighborhood defense gene similarity effects on tree performance: a community transcriptomic approach
The structure and dynamics of ecological communities are ultimately the outcome of the differential demographic rates of individuals. Individual growth and mortality rates largely result from the interaction between an organism's phenotype and the abiotic and biotic environment. Functional traits have been used extensively over the past decade to elucidate links among phenotypes, demography and community dynamics. A fundamental weakness of most functional trait approaches is the use of 'soft' traits associated with resource acquisition to examine how neighbourhood similarity affects tree survival and growth. However, these 'soft' traits are unlikely to be good predictors of similarities among co-occurring species. Less easily measured aspects of organismal function – such as those related to defence – have frequently gone unmeasured. This is particularly problematic for testing important hypotheses in forest ecology, such as the Janzen–Connell hypothesis where focal trees are expected to be at a disadvantage if their neighbours share the same natural enemies. A potential alternative to functional trait approaches is to quantify the transcriptomic or functional genomic similarity of species. Such analyses are now possible in natural systems where de novo transciptome assemblies can be used to conduct functional phylogenomic analyses where homologous gene trees are produced. Using demographic plot data for 21 species from a North American forest dynamic plot, we conduct a community functional phylogenomic analysis of a plant community to elucidate the similarity in defence response genes across species. This similarity was then used to ask whether the similarity in defence genes of heterospecific species in the local neighbourhood of a focal individual tree influences its growth and mortality rates. The results show that individual growth rates are higher when surrounded by dissimilar heterospecific species for 16 of 27 defence genes analysed. Additionally, survival rates are increased when an individual is in a neighbourhood with dissimilar species for 4 of the 27 defence genes studied. Lastly, strong conspecific effects were found in all analyses, underscoring that future analyses investigating the genetic variation and differential expression of defence-related genes in neighbourhoods may prove important. Synthesis. In summary, this research leverages recent advances in RNA sequencing and bioinformatics to conduct community-wide transcriptomic analyses and analyses of defence-related gene similarity across a tree community. The results demonstrate that defence gene similarity in neighbourhoods often does have negative effects on individual demographic performance as predicted by the Janzen–Connell hypothesis.
Data from: Specificity of multi-modal aphid defenses against two rival parasitoids
Insects are often attacked by multiple natural enemies, imposing dynamic selective pressures for the development and maintenance of enemy-specific resistance. Pea aphids (Acyrthosiphon pisum) have emerged as models for the study of variation in resistance against natural enemies, including parasitoid wasps. Internal defenses against their most common parasitoid wasp, Aphidius ervi, are sourced through two known mechanisms– 1) endogenously encoded resistance or 2) infection with the heritable bacterial symbiont, Hamiltonella defensa. Levels of resistance can range from nearly 0–100% against A. ervi but varies based on aphid genotype and the strain of toxin-encoding bacteriophage (called APSE) carried by Hamiltonella. Previously, other parasitoid wasps were found to commonly attack this host, but North American introductions of A. ervi have apparently displaced all other parasitoids except Praon pequodorum, a related aphidiine braconid wasp, which is still found attacking this host in natural populations. To explain P. pequodorum's persistence, multiple studies have compared direct competition between both wasps, but have not examined specificity of host defenses as an indirectly mediating factor. Using an array of experimental aphid lines, we first examined whether aphid defenses varied in effectiveness toward either wasp species. Expectedly, both types of aphid defenses were effective against A. ervi, but unexpectedly, were completely ineffective against P. pequodorum. Further examination showed that P. pequodorum wasps suffered no consistent fitness costs from developing in even highly 'resistant' aphids. Comparison of both wasps' egg-larval development revealed that P. pequodorum's eggs have thicker chorions and hatch two days later than A. ervi's, likely explaining their differing abilities to overcome aphid defenses. Overall, our results indicate that aphids resistant to A. ervi may serve as reservoirs for P. pequodorum, hence contributing to its persistence in field populations. We find that specificity of host defenses and defensive symbiont infections, may have important roles in influencing enemy compositions by indirectly mediating the interactions and abundance of rival natural enemies.
Data from: Cascading effects of induced terrestrial plant defenses on aquatic and terrestrial ecosystem function
Herbivores induce plants to undergo diverse processes that minimize costs to the plant, such as producing defences to deter herbivory or reallocating limited resources to inaccessible portions of the plant. Yet most plant tissue is consumed by decomposers, not herbivores, and these defensive processes aimed to deter herbivores may alter plant tissue even after detachment from the plant. All consumers value nutrients, but plants also require these nutrients for primary functions and defensive processes. We experimentally simulated herbivory with and without nutrient additions on red alder (Alnus rubra), which supplies the majority of leaf litter for many rivers in western North America. Simulated herbivory induced a defence response with cascading effects: terrestrial herbivores and aquatic decomposers fed less on leaves from stressed trees. This effect was context dependent: leaves from fertilized-only trees decomposed most rapidly while leaves from fertilized trees receiving the herbivory treatment decomposed least, suggesting plants funnelled a nutritionally valuable resource into enhanced defence. One component of the defence response was a decrease in leaf nitrogen leading to elevated carbon : nitrogen. Aquatic decomposers prefer leaves naturally low in C : N and this altered nutrient profile largely explains the lower rate of aquatic decomposition. Furthermore, terrestrial soil decomposers were unaffected by either treatment but did show a preference for local and nitrogen-rich leaves. Our study illustrates the ecological implications of terrestrial herbivory and these findings demonstrate that the effects of selection caused by terrestrial herbivory in one ecosystem can indirectly shape the structure of other ecosystems through ecological fluxes across boundaries.
Data from: Changing of the guard: mixed specialization and flexibility in nest defense (Tetragonisca angustula)
Task allocation is a central challenge of collective behavior in a variety of group-living species, and this is particularly the case for the allocation of social insect workers for group defense. In social insects, both benefits and considerable costs are associated with the production of specialized soldiers. We asked whether colonies mitigate costs of production of specialized soldiers by simultaneously employing behavioral flexibility in non-specialist workers that can augment defense capabilities at short time scales. We studied colonies of the stingless bee Tetragonisca angustula, a species that has two discrete nest guarding tasks typically performed by majors: hovering guarding and standing guarding. Majors showed age polyethism across nest-guarding tasks, first hovering and then changing to the task of standing guarding after one week. Colonies were also able to reassign minors to guarding tasks when majors were experimentally removed. Replacement guards persisted in nest defense tasks until colonies produced enough majors to return to their initial state. Tetragonisca angustula colonies thus employed a coordinated set of specialization strategies in nest defense: morphologically specialized soldiers, age polyethism among soldiers within specific guarding tasks, and rapid flexible reallocation of non-specialists to guarding during soldier loss. This mixed strategy achieves the benefits of a highly specialized defensive force while maintaining the potential for rapid reinforcement when soldiers are lost or colonies face unexpectedly intense attack.
FIGURES 9–16. Piestus heterocephalus Fauvel, 1902. 9 in New position of an abdominal defensive gland complex in Staphylinidae (Coleoptera) with redescription of Piestus heterocephalus Fauvel, 1902 (Piestinae)
FIGURES 9–16. Piestus heterocephalus Fauvel, 1902. 9) labrum and epipharynx, left epiphayneal lobe and right setae removed; 10) mandibles, apex in dorsal view; 11) sternites VI and VII, ventral view, gently separated; 12) tergite X, apex, dorsal view; 13–14) aedeagus, 13) lateral view, 14) ventral view; 15) sternite IX, female, ventral view; 16) spermatheca. Scales: 0.25mm, except Fig. 11: 1mm.
FIGURES 1–8. Piestus heterocephalus Fauvel, 1902. 1 in New position of an abdominal defensive gland complex in Staphylinidae (Coleoptera) with redescription of Piestus heterocephalus Fauvel, 1902 (Piestinae)
FIGURES 1–8. Piestus heterocephalus Fauvel, 1902. 1) habitus, dorsal view; 2) habitus, lateral view; 3) head, dorsal view; 4) head, lateral view; 5) sternites VI and VII, ventrolateral view (arrow: external opening of the defensive gland); 6) sternites VI and VII, ventral view; 7) sternites VI and VII, dorsal view, tergites removed, micrograph; 8) micrograph showing details of reservoir and of cell mass.
FIGURE 17. Piestus heterocephalus Fauvel, 1902. Sternites V in New position of an abdominal defensive gland complex in Staphylinidae (Coleoptera) with redescription of Piestus heterocephalus Fauvel, 1902 (Piestinae)
FIGURE 17. Piestus heterocephalus Fauvel, 1902. Sternites V–VII dorsal view, tergites and left reservoir removed. Scale: 1mm.
Fig. 5 in Tiger Beetle Defenses Revisited: Alternative Defense Strategies And Colorations Of Two Neotropical Tiger Beetles, Odontocheila Nicaraguensis Bates And Pseudoxycheila Tarsalis Bates (Carabidae: Cicindelinae)
Fig. 5. Mean radiance spectra (error bars = 1 SD) of the three patches in the elytral color pattern of Pseudoxycheila tarsalis under the ambient light conditions of a large gap.
Figure 4 in Tiger Beetle Defenses Revisited: Alternative Defense Strategies And Colorations Of Two Neotropical Tiger Beetles, Odontocheila Nicaraguensis Bates And Pseudoxycheila Tarsalis Bates (Carabidae: Cicindelinae)
Figure 4. Mean reflectance spectra (error bars = 1 SD) of the three patches in the elytral color pattern of Pseudoxycheila tarsalis, and the reflectance of clay soil samples from Monteverde, Costa Rica.
Fig. 1 in Tiger Beetle Defenses Revisited: Alternative Defense Strategies And Colorations Of Two Neotropical Tiger Beetles, Odontocheila Nicaraguensis Bates And Pseudoxycheila Tarsalis Bates (Carabidae: Cicindelinae)
Fig. 1. Mean reflectance spectra (error bars = 1 SD) for the abdomen and elytra of Odontocheila nicaraguensis and the leaf litter substrate at La Selva.
Fig. 3 in Tiger Beetle Defenses Revisited: Alternative Defense Strategies And Colorations Of Two Neotropical Tiger Beetles, Odontocheila Nicaraguensis Bates And Pseudoxycheila Tarsalis Bates (Carabidae: Cicindelinae)
Fig. 3. Mean radiance spectra (error bars = 1 SD) for the abdomen and elytra of Odontocheila nicaraguensis under ambient light conditions in the forest understory at La Selva, Costa Rica.
Fig. 6. A in Tiger Beetle Defenses Revisited: Alternative Defense Strategies And Colorations Of Two Neotropical Tiger Beetles, Odontocheila Nicaraguensis Bates And Pseudoxycheila Tarsalis Bates (Carabidae: Cicindelinae)
Fig. 6. A comparison of the mean reflectance spectra (error bars = 1 SD) for the white spots and black fields of P. tarsalis and the mutillid wasp Hoplomutilla sp.
Fig. 2 in Tiger Beetle Defenses Revisited: Alternative Defense Strategies And Colorations Of Two Neotropical Tiger Beetles, Odontocheila Nicaraguensis Bates And Pseudoxycheila Tarsalis Bates (Carabidae: Cicindelinae)
Fig. 2. Mean radiance (error bars = 1 SD) spectra for the abdomen and elytra of Odontocheila nicaraguensis under ambient light conditions of large gaps at La Selva, Costa Rica.
Defensive phragmosis and cathaptosis in Trichoptera larvae
<p>Phragmosis, or the use of specially modified body parts and associated behaviors to block an opening as defense against predators, is a commonly observed phenomenon in certain ants and termites that block entrances of their subterranean nests with large, flat heads. It has been reported in some beetles and other insects and even in some frogs. Common features of phragmosis in caddisfly larvae include a hard and usually flat body surface, with or without stout spines, and the behavior of fitting that body surface tightly in the opening of its case. A different defensive strategy occurs in snails and case-making larvae of camptosomate leaf beetles (Chrysomelidae: Cryptocephalinae and Lamprosomatinae) that protect themselves from predators by securing the openings of their shells or cases firmly against the substrate, a behavior we call "cathaptosis." Common features of cathaptosis in caddisfly larvae include a case with its vulnerable opening oriented parallel with the substrate and accompanied by behavior that grips the substrate, fixing the case opening firmly against it when threatened. We suggest that these defensive strategies have evolved multiple times in Trichoptera, especially in case-making larvae. We demonstrate some examples and provide tentative lists of caddisflies whose larvae may have evolved these defensive strategies.</p>
Division of labor for defensive retaliation and preemption by the peripheral and central nervous systems in the nudibranch Berghia stephanieae
<p>Contained in this depository are the kinematic data, associated analyses, and original MATLAB code accompanying the paper "Division of labor for defensive retaliation and preemption by the peripheral and central nervous systems in the nudibranch <em>Berghia stephanieae.</em>" </p>
Fig. 2 in Characterized constituents of insect herbivore oral secretions and their influence on the regulation of plant defenses
Fig. 2. Representative plant defensive metabolites (potential markers) induced upon insect feeding and application of insect OS on wounded plants. Specific group of metabolites are induced in plants belonging to particular families. (a) Solanaceae; terpenoids, phenolics, alkaloids (b) Bracecaceae; glucosinolates, cyanogenic glycosides, saponins and (c) Poaceae; benzoxazinoids.
Fig. 1 in Characterized constituents of insect herbivore oral secretions and their influence on the regulation of plant defenses
Fig. 1. Schematic presentation of identified bioactive molecules from the oral secretion/mouthpart of insects. Active molecules were characterized as inducer or suppressor of plant defense. Fatty acid amino acid conjugates (FACs) elicit volatile emission and isoflavonid synthesis. Proteinaceous elicitors induces Jasmonic acid (JA) and Salicylic acid (SA) biosynthesis and signaling leading to induce plant defense by protease inhibitors synthesis and release of volatiles. The Glucose Oxidase (GOX) induces reactive oxygen species (ROS) through hydrogen peroxide H2O2. Proteinaceous effectors either suppress the hydrogen peroxide H2O2, JA/SA biosynthesis and signaling or the interaction of transcription factors (WRKY) with kinases.
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