Defense Allocation Research Articles

Insect herbivores, chemical innovation, and the evolution of habitat specialization in Amazonian trees

Herbivores are often implicated in the generation of the extraordinarily diverse tropical flora. One hypothesis linking enemies to plant diversification posits that the evolution of novel defenses allows plants to escape their enemies and expand their ranges. When range expansion involves entering a new habitat type, this could accelerate defense evolution if habitats contain different assemblages of herbivores and/or divergent resource availabilities that affect plant defense allocation. We evaluated this hypothesis by investigating two sister habitat specialist ecotypes of Protium subserratum (Burseraceae), a common Amazonian tree that occurs in white-sand and terra firme forests. We collected insect herbivores feeding on the plants, assessed whether growth differences between habitats were genetically based using a reciprocal transplant experiment, and sampled multiple populations of both lineages for defense chemistry. Protium subserratum plants were attacked mainly by chrysomelid beetles and cicadellid hemipterans. Assemblages of insect herbivores were dissimilar between populations of ecotypes from different habitats, as well as from the same habitat 100 km distant. Populations from terra firme habitats grew significantly faster than white-sand populations; they were taller, produced more leaf area, and had more chlorophyll. White-sand populations expressed more dry mass of secondary compounds and accumulated more flavone glycosides and oxidized terpenes, whereas terra firme populations produced a coumaroylquinic acid that was absent from white-sand populations. We interpret these results as strong evidence that herbivores and resource availability select for divergent types and amounts of defense investment in white-sand and terra firme lineages of Protium subserratum, which may contribute to habitat-mediated speciation in these trees.

Early Root Herbivory Impairs Arbuscular Mycorrhizal Fungal Colonization and Shifts Defence Allocation in Establishing Plantago lanceolata.

Research into plant-mediated indirect interactions between arbuscular mycorrhizal (AM) fungi and insect herbivores has focussed on those between plant shoots and above-ground herbivores, despite the fact that only below-ground herbivores share the same part of the host plant as AM fungi. Using Plantago lanceolata L., we aimed to characterise how early root herbivory by the vine weevil (Otiorhynchus sulcatus F.) affected subsequent colonization by AM fungi (Glomus spp.) and determine how the two affected plant growth and defensive chemistry. We exposed four week old P. lanceolata to root herbivory and AM fungi using a 2×2 factorial design (and quantified subsequent effects on plant biomass and iridoid glycosides (IGs) concentrations. Otiorhynchus sulcatus reduced root growth by c. 64%, whereas plant growth was unaffected by AM fungi. Root herbivory reduced extent of AM fungal colonization (by c. 61%). O. sulcatus did not influence overall IG concentrations, but caused qualitative shifts in root and shoot IGs, specifically increasing the proportion of the more toxic catalpol. These changes may reflect defensive allocation in the plant against further attack. This study demonstrates that very early root herbivory during plant development can shape future patterns of AM fungal colonization and influence defensive allocation in the plant.

Drought-induced trans-generational tradeoff between stress tolerance and defence: consequences for range limits?

Areas just across species range boundaries are often stressful, but even with ample genetic variation within and among range-margin populations, adaptation towards stress tolerance across range boundaries often does not occur. Adaptive trans-generational plasticity should allow organisms to circumvent these problems for temporary range expansion; however, range boundaries often persist. To investigate this dilemma, we drought stressed a parent generation of Boechera stricta (A.Gray) A. Löve & D. Löve, a perennial wild relative of Arabidopsis, representing genetic variation within and among several low-elevation range margin populations. Boechera stricta is restricted to higher, moister elevations in temperate regions where generalist herbivores are often less common. Previous reports indicate a negative genetic correlation (genetic tradeoff) between chemical defence allocation and abiotic stress tolerance that may prevent the simultaneous evolution of defence and drought tolerance that would be needed for range expansion. In growth chamber experiments, the genetic tradeoff became undetectable among offspring sib-families whose parents had been drought treated, suggesting that the stress-induced trans-generational plasticity may circumvent the genetic tradeoff and thus enable range expansion. However, the trans-generational effects also included a conflict between plastic responses (environmental tradeoff); offspring whose parents were drought treated were more drought tolerant, but had lower levels of glucosinolate toxins that function in defence against generalist herbivores. We suggest that either the genetic or environmental tradeoff between defence allocation and stress tolerance has the potential to contribute to range limit development in upland mustards.

Defending a Star: Coordinating the Defense of a Network

This experiment focuses on a contest played over a star network of 6 nodes. By placing targets in a network, the value of a target is dependent on its connectivity to other targets. The experiment compares the cases where the defense is centrally planned by a defense planner with a case where the defense is coordinated by six individuals each placed at one node in the network. By additionally varying how many targets the attacker may target, the experimental design consists of a 2 x 2 design. Attackers tend to over exert e ort on the Center Node whereas defenders tend to place too little e ort on the Center Node (with one exception). These attack and defense allocations lead to defenders earning smaller than equilibrium pro ts (again with one exception). It appears that Defense Planners manage to plan a defense better than the Coordinated Defenders when facing an attacker who may only target one node. However, Defense Planners are not certain to perform better than Coordinated Defenders as the Planner earns a smaller pro t on average (but is less volatile in his earnings).

Nitrogen enrichment differentially affects above‐ and belowground plant defense

Human nitrogen (N) inputs to terrestrial ecosystems have greatly increased in recent years and may have important consequences for plant growth, reproduction, and defense. Although numerous studies have investigated the effects of nitrogen addition on plants, few have examined both above- and belowground responses within a range of predicted increase and apart from concomitant increases in other nutrients. • We conducted a greenhouse experiment to study the consequences of increased nitrogen inputs, such as those from atmospheric N deposition, on plant performance, chemical defenses, and allocation tradeoffs for an invasive species, Linaria dalmatica. This plant produces iridoid glycosides, which are a group of terpenoid compounds. • Soil nitrogen enrichment increased growth, reproduction, and whole-plant iridoid glycosides while decreasing some costs of defense. Interestingly, nitrogen addition had varying effects on defense allocation to above- and belowground tissues. Specifically, there was no change in iridoid glycoside concentrations of shoots, whereas concentrations decreased in flowers by ~35% and increased in roots by >400%. • Observed increases in plant performance and chemical defenses may have implications for the invasion potential of L. dalmatica. Moreover, our results highlight the importance of evaluating both above- and belowground plant defenses. In particular, findings presented here indicate that research focused on leaf-level defenses may not detect key allelochemical responses, including changes in plant resistance traits that could affect consumers (e.g., herbivores and pathogens) that specialize on different plant tissues as well as plant fitness and invasion success.

Defence on demand: mechanisms behind optimal defence patterns

The optimal defence hypothesis (ODH) predicts that tissues that contribute most to a plant's fitness and have the highest probability of being attacked will be the parts best defended against biotic threats, including herbivores. In general, young sink tissues and reproductive structures show stronger induced defence responses after attack from pathogens and herbivores and contain higher basal levels of specialized defensive metabolites than other plant parts. However, the underlying physiological mechanisms responsible for these developmentally regulated defence patterns remain unknown. This review summarizes current knowledge about optimal defence patterns in above- and below-ground plant tissues, including information on basal and induced defence metabolite accumulation, defensive structures and their regulation by jasmonic acid (JA). Physiological regulations underlying developmental differences of tissues with contrasting defence patterns are highlighted, with a special focus on the role of classical plant growth hormones, including auxins, cytokinins, gibberellins and brassinosteroids, and their interactions with the JA pathway. By synthesizing recent findings about the dual roles of these growth hormones in plant development and defence responses, this review aims to provide a framework for new discoveries on the molecular basis of patterns predicted by the ODH. Almost four decades after its formulation, we are just beginning to understand the underlying molecular mechanisms responsible for the patterns of defence allocation predicted by the ODH. A requirement for future advances will be to understand how developmental and defence processes are integrated.

Long-term plasticity in growth, storage and defense allocation produces drought-tolerant juvenile shrubs of Prosopis alpataco R.A. Philippi (Fabaceae)

Evaluation of phenotypic plasticity of plants is important to predict the long-term fate of populations exposed to environmental change. Climate scenarios predict a decrease in rainfall and increase in temperature for Northern Patagonia (Argentina). The long-term assessment of the effect of water shortage on allocation patterns of Prosopis alpataco provides insights into how climate change could affect this dominant shrub of the Monte Desert. A single-factor (water supply) field experiment was conducted. Phenotypic plasticity in biomass partitioning and allocation to storage and defense was assessed over the course of pre-reproductive growth during five years. Water-effect and size-dependent effects were sorted out. Our results indicate that as plants grow larger, root:shoot ratio increases, as well as total non-structural carbohydrates pool, irrespective of water treatment. Increasing belowground allocation through partitioning to reserves instead of allocation to non-storage mass, favors carbohydrate forms that later can be mobilized. Spine mass ratio increased 3-fold in response to drought. These conservative strategies might facilitate the persistence of Prosopis alpataco in a novel and drier environment, through the production of drought-tolerant juvenile individuals.

The spiny, thorny and prickly plants in the flora of Israel

To examine whether spininess evolved at random or differently in various life forms and plant organs, we characterized spiny, thorny and prickly organs in the entire wild flora of Israel (294 such species). Of the species, 63.3% defended their reproductive organs (the most-defended organ) and 67.0% defended various non-reproductive organs. Ninety-three species defended both their reproductive organs and at least one other part; 48.3% defended their leaves and 36.4% their stems and branches. Spiny wings defended stems and branches only in herbaceous (annual or perennial) species. There were clear differences between the life forms. Annuals and perennial herbs defended mostly their reproductive organs (95.7 and 83.0%, respectively), dwarf shrubs defended mostly their leaves (54.2%) and shrubs and trees mostly their branches (89.7 and 76.2%, respectively). Trees do not defend their reproductive organs by associated sharp appendages. The differences in defence on various organs among different life forms may influence the results of meta-analysis studies of the optimal defence allocation if such differences are not taken into account. We noted spine, thorn and prickle colours for 167 species with yellow, red, orange and white being the dominant, supporting hypotheses about spines being visually aposematic. © 2012 The Linnean Society of London, Botanical Journal of the Linnean Society, 2012, 168, 344–352.

Water deficiency induces evolutionary tradeoff between stress tolerance and chemical defense allocation that may help explain range limits in plants

What causes range limits is a central question in evolutionary ecology. Transplant studies indicate that areas just across range boundaries are often stressful. The recent Defense constraint (DC) hypothesis for plants states that the evolution of tolerance to stressful environments across a range boundary is constrained by allocation to chemical defense because of antagonistic crosstalk between abiotic and biotic stress signaling pathways that otherwise could be co‐opted for range expansion. Abscisic acid (ABA) drought stress tolerance and jasmonic acid/ethylene (JA/ET) defense signaling pathways, for example, are known to be antagonistic to one another in Arabidopsis and other species. To test the DC hypothesis, we examined quantitative genetic variation and co‐variation among marker‐inferred inbred lines and sib‐families of Boechera stricta, a close wild relative of Arabidopsis. The dynamics of the defense‐stress tolerance tradeoff was examined across 1) years that differed in precipitation, 2) drought and ABA treatments, and 3) a NPK nutrient supply gradient. In support of the DC hypothesis, we observed the tradeoff a) in the dry year, and b) in response to water deficiency, which c) was affected by ABA treatments, but the interaction between ABA and glucosinolate (GS) toxin levels was not significant. In contrast to the effects of water deficiency, d) the effect of lower NPK supply to cause the tradeoff was only marginally significant. Because an ABA‐mediated stress response is intrinsic to water deficient conditions and because of the known involvement of JA/ET in GS regulation, we suggest that these results provide circumstantial evidence implicating both of these pathways in the tradeoff and thus in the development of range limits.

The elemental stoichiometry of aquatic and terrestrial ecosystems and its relationships with organismic lifestyle and ecosystem structure and function: a review and perspectives

C, N and P are three of the most important elements used to build living beings, and their uptake from the environment is consequently essential for all organisms. We have reviewed the available studies on water, soils and organism elemental content ratios (stoichiometry) with the aim of identifying the general links between stoichiometry and the structure and function of organisms and ecosystems, in both aquatic and terrestrial contexts. Oceans have variable C:N:P ratios in coastal areas and a narrow range approximating the Redfield ratio in deep water and inner oceanic areas. Terrestrial ecosystems have a general trend towards an increase in soil and plant N:P ratios from cool and temperate to tropical ecosystems, but with great variation within each climatic area. The C:N:P content ratio (from now on C:N:P ratio) is more constrained in organisms than in the water and soil environments they inhabit. The capacity to adjust this ratio involves several mechanisms, from leaf re-absorption in plants to the control of excretion in animals. Several differences in C:N:P ratios are observed when comparing different taxa and ecosystems. For freshwater ecosystems, the growth rate hypothesis (GRH), which has consistent experimental support, states that low N:P supply determines trophic web structures by favoring organisms with a high growth rate. For terrestrial organisms, however, evidence not yet conclusive on the relevance of the GRH. Recent studies suggest that the N:P ratio could play a role, even in the evolution of the genomes of organisms. Further research is warranted to study the stoichiometry of different trophic levels under different C:N:P environment ratios in long-term ecosystem-scale studies. Other nutrients such as K or Fe should also be taken into account. Further assessment of the GRH requires more studies on the effects of C:N:P ratios on anabolic (growth), catabolic (respiration), storage and/or defensive allocation. Combining elemental stoichiometry with metabolomics and/or genomics should improve our understanding of the coupling of different levels of biological organization, from elemental composition to the structure and evolution of ecosystems, via cellular metabolism and nutrient cycling.

The relationship between leaf nitrogen, nitrogen metabolites and herbivory in two species of Nyctaginaceae from the Brazilian Cerrado

Guapira graciliflora and Neea theifera are taxonomically related species of the tribe Pisoneae. Both species are found in the same environment, the Brazilian Cerrado, and therefore, are subjected to similar selective pressures. These species occur in oligotrophic environments, yet contain high concentrations of nitrogen in their leaves. The present study was carried out to investigate the ecological role of nitrogen in herbivory on these species. The differences in the N content, compositions of secondary N-metabolites, mechanical resistance, and water content between their leaves indicate that these species have different adaptations as defense mechanisms. In both species, their high nitrogen content seems to promote herbivory. The presence of secondary nitrogen metabolites does not prevent the species from suffering intense damage by herbivores on their early leaves. The herbivory rates observed were lower for mature leaves of both species than for young leaves. In G. graciliflora, nutritional content and leaf hardness are the most important variables correlated with reduction of herbivory rates, whereas in N. theifera, N compounds are also correlated with herbivory rates. Despite the differences in the strategies of these two species, they exhibit a similar efficiency of protection against natural enemies because their total herbivory rates are similar. The difference in their N defense allocation may imply benefits for survival under Cerrado conditions. We briefly discuss the oligotrophic habitat conditions of the studied plants and possible advantages of their strategies of N accumulation and metabolic uses.

Modeling Arbitrary Layers of Continuous‐Level Defenses in Facing with Strategic Attackers

We propose a novel class of game-theoretic models for the optimal assignment of defensive resources in a game between a defender and an attacker. Compared to the other game-theoretic models in the literature of defense allocation problems, the novelty of our model is that we allow the defender to assign her continuous-level defensive resources to any subset (or arbitrary layers) of targets due to functional similarity or geographical proximity. We develop methods to solve for equilibrium, and illustrate our model using numerical examples. Compared to traditional models that only allow for individual target hardening, our results show that our model could significantly increase the defender's payoff, especially when the unit cost of defense is high.

Optimal defense: snails avoid reproductive parts of the lichen Lobaria scrobiculata due to internal defense allocation

The optimal defense theory (ODT) deals with defensive compounds improving fitness of a particular organism. It predicts that these compounds are allocated in proportion to the risk for a specific plant tissue being attacked and this tissue's value for plant fitness. As the benefit of defense cannot easily be measured in plants, the empirical evidence for ODT is limited. However, lichens are unique in the sense that their carbon-based secondary compounds can nondestructively be removed or reduced in concentration by acetone rinsing. By using such an extraction protocol, which is lethal to plants, we have tested the ODT by studying lichens instead of plants as photosynthetically active organisms. Prior to acetone rinsing, we found five times higher concentration of meta-scrobiculin in the reproductive parts (soralia) of Lobaria scrobiculata compared to somatic parts of this foliose epiphytic lichen species. At this stage, the lichen-feeding snail Cochlodina laminata avoided the soralia. However, after removal of secondary compounds, the snail instead preferred the soralia. In this way, we have successfully shown that grazing pattern inversely reflects the partitioning of the secondary compounds that have a documented deterring effect. Thus our study provides strong and novel evidence for the ODT.

Direct and indirect root defences of milkweed (Asclepias syriaca): trophic cascades, trade‐offs and novel methods for studying subterranean herbivory

Summary 1. Entomopathogenic nematodes can function as indirect defence for plants that are attacked by root herbivores. By releasing volatile organic compounds (VOCs), plants signal the presence of host insects and thereby attract nematodes. 2. Nonetheless, how roots deploy indirect defences, how indirect defences relate to direct defences, and the ecological consequences of root defence allocation for herbivores and plant biomass are essentially unknown. 3. We investigate a natural below‐ground tritrophic system, involving common milkweed, a specialist root‐boring beetle and entomopathogenic nematodes, and asked whether there is a negative genetic correlation between direct defences (root cardenolides) and indirect defences (emission of volatiles in the roots and nematode attraction), and between constitutive and inducible defences. 4. Volatiles of roots were analysed using two distinct sampling methods. First, we collected emissions from living Asclepias syriaca roots by dynamic headspace sampling. This method showed that attacked A. syriaca plants emit five times higher levels of volatiles than control plants. Secondly, we used a solid phase micro‐extraction (SPME) method to sample the full pool of volatiles in roots for genetic correlations of volatile biosynthesis. 5. Field experiments showed that entomopathogenic nematodes prevent the loss of biomass to root herbivory. Additionally, suppression of root herbivores was mediated directly by cardenolides and indirectly by the attraction of nematodes. Genetic families of plants with high cardenolides benefited less from nematodes compared to low‐cardenolide families, suggesting that direct and indirect defences may be redundant. Although constitutive and induced root defences traded off within each strategy (for both direct and indirect defence, cardenolides and VOCs, respectively), we found no trade‐off between the two strategies. 6. Synthesis. Constitutive expression and inducibility of defences may trade off because of resource limitation or because they are redundant. Direct and indirect defences do not trade off, likely because they may not share a limiting resource and because independently they may promote defence across the patchiness of herbivore attack and nematode presence in the field. Indeed, some redundancy in strategies may be necessary to increase effective defence, but for each strategy, an economy of deployment reduces overall costs.

To be resistant or tolerant: the evolution of mixed defence strategies

AbstractTheory predicts that resistance and tolerance represent mutually exclusive strategies of host defence. However, empirical evidence reveals that individual hosts simultaneously allocate resources to both mechanisms. Understanding the maintenance of this defence pattern remains controversial because empirical evidence is at odds with theoretical assumptions. Here, we present a novel host-enemy dynamic that considers: the differential effect of each defence strategy upon the evolutionary response of natural enemies; the process of local adaptation of the natural enemies to their hosts and the effect of negative and positive frequency-dependent selection acting on resistance and tolerance respectively. Our analysis suggests that a mixed pattern of defence allocation could be evolutionary stable because of the differential dynamic that each strategy has in the interaction with natural enemies.

Specificity and trade‐offs in the induced plant defence of common milkweed Asclepias syriaca to two lepidopteran herbivores

Summary 1. We studied induced defences in common milkweed (Asclepias syriaca) to two specialist caterpillars (Danaus plexippus and Euchaetes egle) to test several hypotheses about co‐evolution and defence allocation. 2. Latex, a potent defence of milkweed, showed nearly fivefold variation in the amount exuded among genetic families and more than doubled production in response to herbivory by D. plexippus; this induced latex response was fourfold stronger than the latex response to E. egle herbivory. In contrast, D. plexippus and E. egle equivalently induced foliar cardenolide concentration (an average increase of 26%). 3. We found broad‐sense heritable variation for the induced plant responses, and there was a genetic correlation between the responses induced by the two herbivores for cardenolides, but not for latex. We found no genetic correlation between investment in latex and cardenolides in any of the treatments. 4. Using a bias‐corrected Monte Carlo procedure, we found strong evidence for a trade‐off between constitutive and induced cardenolides, but not for latex. 5. Synthesis. As natural selection by specific herbivores varies in space and time, we expect that these defence traits in A. syriaca will evolve independently, with the expression of cardenolides showing less specificity, as well as being constrained by a trade‐off between constitutive and induced defence.

Can optimal defence theory be used to predict the distribution of plant chemical defences?

Summary 1. The optimal defence theory (ODT) of chemical defence provides a predictive framework for the distribution of anti‐herbivore defences in plants. One of its predictions is that chemical defences will be allocated within a plant as a function of tissue value, where value is correlated with the cost of having that tissue removed. While many studies have examined intra‐plant variation in defence chemistry, these results have rarely been compiled quantitatively to assess whether defence allocation is consistent with the prediction of ODT that more valuable tissues should be more defended than less valuable tissues. 2. We performed a formal meta‐analysis of published and unpublished studies to examine the predictive utility of ODT. Specifically, we examined whether defence chemicals occur at higher concentrations in flowers versus leaves and in younger leaves compared to older leaves, under the assumption that younger leaves are more valuable than older leaves. We also examined whether the expansion status of younger leaves, nodal position of the leaves, growing conditions and chemical class of defence compounds affected the mean effect sizes. 3. We found that tissues with higher assumed value had significantly higher concentrations of defence chemicals than tissues with lower value. In particular, we found that younger leaves had higher concentrations of defence chemicals than older leaves, consistent with the predictions of ODT. The magnitude of this difference was higher in the younger leaf/older leaf comparison than in the flower/leaf comparison, with no evidence that flowers were more defended than leaves. The overall results were not affected by chemical class, young leaf expansion status, growing conditions or leaf position on the plant. 4. Synthesis. We found general agreement between the predictions of ODT and the intraplant distribution of chemical defence and conclude it is a useful model. The effect size varied depending on the tissue compared. Explicit measures of tissue value, in particular as it relates to relative fitness, are required to further validate the predictive utility and general applicability of ODT.

The impacts of adaptive attacking and defending strategies on mitigation of intentional threats

PurposeThe purpose of this paper is to focus on resource allocation and information disclosure policy for defending multiple targets against intentional attacks. The intentional attacks, like terrorism events, probably cause great losses and fatalities. Attackers and defenders usually make decisions based on incomplete information. Adaptive attacking and defending strategies are considered, to study how both sides make more effective decisions according to previous fights.Design/methodology/approachA stochastic game‐theoretic approach is proposed for modeling attacker‐defender conflicts. Attackers and defenders are supposed both to be strategic decision makers and partially aware of adversary's information. Adaptive strategies are compared with different inflexible strategies in a fortification‐patrol problem, where the fortification affects the security vulnerability of targets and the patrol indicates the defensive signal.FindingsThe result shows that the intentional risk would be elevated by adaptive attack strategies. An inflexible defending strategy probably fails when facing uncertainties of adversary. It is shown that the optimal response of defenders is to adjust defending strategies by learning from previous games and assessing behaviors of adversaries to minimize the expected loss.Originality/valueThis paper explores how adaptive strategies affect attacker‐defender conflicts. The key issue is defense allocation and information disclosure policy for mitigation of intentional threats. Attackers and defenders can adjust their strategies by learning from previous fights, and the strategic adjustment of both sides may be asynchronous.

Optimal Defense Schedule of Annual Plants against Seasonal Herbivores

Herbivores often have huge impacts on plant performance. In order to reduce damage from herbivory, plants evolve antiherbivore defenses, the mechanisms of which have been studied from a theoretical viewpoint. In the theoretical studies, the models of defense schedules have assumed a uniform intensity of herbivory or a constant rate of encounter of herbivores throughout the season. However, some herbivores apparently appear for only a limited period instead of the whole growing season of the plant. In our study, we analyzed the optimal schedule of defense allocation of the plant under the herbivory that occurs within a limited period with a certain probability. We assumed an annual plant that consists of vegetative and defensive parts and whose growing season is divided into two phases at the time of herbivore emergence. In the phase after the emergence time, the status of a plant can be either with or without herbivore stochastically. The plant is considered to maximize the average vegetative size at the end of the growing season. We found that under the fixed emergence time, inducible defense is favored when the plant growth rate and herbivory intensity are high. Extending this result, we also analyzed the coevolution of plant defense and herbivore emergence time by using invasibility analysis. In the system considered, an equilibrium steady state tends to be absent in herbivore strategy. This suggests polymorphism of herbivore emergence time.

Chemical defenses, nutritional quality, and structural components in three sponge species: Ircinia felix, I. campana, and Aplysina fulva

Allocating chemical defenses to regions or tissues most at risk for predatory attack may provide protection while simultaneously minimizing associated metabolic costs. Chemical defense allocation patterns were investigated in the aspiculate sponges Ircinia felix, I. campana, and Aplysina fulva collected between July 2005 and April 2006 from J Reef off the coast of Georgia, U.S.A. It was predicted that chemical defenses would be (1) higher in the outermost 2 mm layer of the sponge; (2) positively correlated with tissue nutritional quality; and (3) correlated with structural components such as spongin fibers. Whereas defensive chemicals were concentrated in the outer 2 mm of A. fulva, the Ircinia species had higher concentrations in deeper tissue layers. Furthermore, no significant positive or negative correlation between chemical defenses and nutritional quality or levels of structural components was observed in these sponges. Overall, these results do not support the prediction that predation pressure by fish and large mobile invertebrates significantly impacts chemical defense allocation in these sponges.