Variability chemical defense

Schnitzler I, Boland W, Hay ME (1998) Organic sulfur compounds from Dictyopteris spp. deter feeding by an herbivorous amphipod (Ampithoe longimana) but not by a herbivorous sea urchin (Arbaciapimctulata). J Chem Ecol 24 1715-1732 Shen Y, T sai PI, Fenical W, Hay ME (1993) Secondary metabolite chemistry of the Caribbean marine alga Sporochnus bolleanus. a basis for herbivore chemical defense. Phytochemistry 32 71-75 Schupp PJ, Paul VJ (1994) Calcium carbonate and secondary metabolites in tropical seaweeds variable effects on herbivorous fishes. Ecology 75 1172-1185 Smit AJ (2004) Medicinal and pharmaceutical uses of seaweed natural products a review. J Appl Phycol 16 245-262... 

Case Study of F. vesiculosus in the Eutrophic Northern Baltic Sea Genotypically Variable, Plastic Phlorotannins as Chemical Defenses... 

Determining costs of secondary metabolites is inherentiy difficult as a result of the variable responses, multiple physiological roles of the metabolites, as well as the different types of costs involved in the production of secondary metabolites (production, transport, storage, maintenance) (Strauss et al. 2002). Emerging studies are now taking more of these variables into consideration. For example, work with clonal populations of D. pulchra has estimated costs of furanone production in relation to chemical defense and phenotype by investigations of reproductive... 

The major role of chemical defenses in plants is hypothesized to be increasing the impact of insect diseases, parasites, and predators. None of these factors alone provides an explanation of why evolutionarily labile insects rarely defoliate their long-lived hosts. However, interactions among all of them could increase the useful evolutionary lifetime of each and the effectiveness of all. In particular, chemical variability is observed to place insects in compromise situations which increase their exposure and susceptibility to natural enemies. 

I suggest that variable plant chemistry, by restricting resource availability and focusing the activities of herbivores on a few tissues, promotes compromises between food-finding and risks from natural enemies which are not readily countered by most insects. The spatial and temporal heterogeneity which appears to be common in forest trees is the most important part of the tree s defensive system, and is the only way a plant s chemical defenses can remain effective over evolutionary time. This variable impact on natural enemies may be more important in regulating consumption than any single factor can be. 

Knowledge of the variability in the susceptibility of different guilds and species of mobile invertebrates to chemical defenses produced by sessile invertebrates and seaweeds is critical for a mechanistic understanding of the distribution of the sessile benthos in the sea. Large mobile invertebrates like sea urchins commonly alter benthic community composition from palatable to unpalatable species.92,93 Most notably, chemical defenses produced by tropical seaweeds have been widely implicated in the persistence of these species in areas of intense herbivory like coral reefs1,3 (also see Chapter 6 in this volume). 

At this point, our knowledge of spatial variation in secondary metabolite concentrations across scales of meters to hundreds of kilometers is limited. In some species, there is more variation in chemical defense concentrations within populations than among populations.37-38 In other species, there can be significant variation in secondary metabolite concentrations among populations.18 33 37,42 47 However, these differences may be seasonal or vary from year to year.20-41 47 Further work is needed to better understand the degree of variability that occurs in secondary metabolite concentrations across algal populations and to understand the causes of this variability. 

Many intertidal and shallow subtidal habitats are highly variable over space or time. Consequently, the concentrations of chemical defenses that are appropriate at one place or time may be inappropriate at another. A strategy for dealing with this variability is the detection of an environmental cue that can be correlated with an appropriate level of defense for that environment at that time. One of the best examples of environmental cues causing changes in chemical defense concentrations are herbivore-induced defenses in which chemical levels are increased in response to an attack by a consumer.136 137 Induced defenses require that herbivory be variable and unpredictable, that the inducing cues produce effective increases in defenses, and that the induction is cost-effective and rapid enough to deter further consumption.140... 

Swearingen, D. C., Ill and Pawlik, J. R., Variability in the chemical defense of the sponge Chondrilla nucula against predatory reef fishes, Mar. Biol., 131, 619, 1998. 

Secondary chemistry differs from primary chemistry principally in its distributional variability and it is this variability that has intrigued ecologists for the past 30 years. Theories [or provisional hypotheses (35)] to account for the structural differentiation and function of secondary metabolites, as well as the differential allocation of energy and materials to defensive chemistry, abound, but they are almost exclusively derived from studies of plant-herbivore interactions (Table 2). This emphasis may be because the function of secondary chemicals in plants is less immediately apparent to humans, who have historically consumed a broad array of plants without ill effects, so alternative explanations of their presence readily come to mind. The fact that animals upon disturbance often squirt, dribble, spray, or otherwise release noxious substances at humans and cause pain leads to readier acceptance of a defensive function [although there are skeptics who are unconvinced of a... 

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