Alkaloid sequestration

In a sense, alkaloidal sequestration constitutes the transfer of compounds from the producer to the receiver (predator). In effect, this transfer effectively arms the predator with at least some of the alkaloidal defenses of the ingested plant or animal, probably at little energetic expense to the receiver. Significantly, if a specialist herbivore feeds on an alkaloid-rich plant, it is adapted to tolerate these... 

Hantak MM, Grant T, Reinsch S, Mcginnity D, Loring M, ToyookaN, et al. Dietary Alkaloid Sequestration in a poison frog and experimental test of alkaloid uptake in Melanophryniscus stelzneri (Bufonidae). J Chem Ecol 2013 39(ll-12) 1400-6. 

Keywords. Pyrrolizidine alkaloids (plants). Chemical diversification. Alkaloid sequestration (insects), Chemical defense, Chemical ecology... 

Abstract Alkaloids are a special group of secondary compounds and are part of an organism s adaptation mechanism to its living environment. They are not toxic when stored, but become toxic as a result of cell pH change. The defensive function of alkaloids is only secondary, and connected to internal immune and regulation processes. Animal responses to alkaloids are very diverse. Some animals can tolerate alkaloids relatively well, while others are harmed or even poisoned by them. Animal behaviour in relation to alkaloids depends on evolutionary and co-evolutionary factors. Sequestration of alkaloids is connected with these processes. Alkaloids are a part of plant-derived nutrition. A selective toxicity of these compounds in vertebrates is clearly observed. Vertebrates have the capacity to recognize alkaloids. 

Animal sequestration of alkaloids is connected not only with taste but also with the toxicity of these compounds. It has been stated that the toxicity of alkaloids is very selective. Aniszewski has published data with some LDjq coefficients for some alkaloids and some pesticides and compared their toxicity from a selectivity point of view. There was clear evidence that alkaloids (sparteine and lupanine) are much more toxic for vertebrates than are some pesticides (e.g. malafione, phenitrothione, etc.). For invertebrates, pesticides were clearly more toxic than alkaloids. Selective toxicity coefficients (STC) were counted by dividing the LDjg for vertebrates by the LDjg for invertebrates. When the STC is 1.0 there is no selectivity when STC is >1 there is invertebrate selectivity and when <1 there is vertebrate selectivity. Selectivity simply means there exists more ability to toxify the organism. 

The sequestration of alkaloids by insects is considered to be a form of defence. Insects sequester alkaloids and accumulate them for protection against their... 

However, in the case of dietary alkaloids, it would seem that more than only traces of alkaloids, which do not exhibit selective toxicity to antagonist organisms, would be needed for defensive purposes. These trace alkaloids probably have a role in the organism s metabolism, development and behaviour. The traces of alkaloids in the eggs of Arctia caja also suggest a potential participation of these compounds in reproduction. Moreover, attention should be given to the fact that alkaloids are dietary sequestrations acquired from feeding on plants. 

Dobler, S., Haberer, W., Witte, L. and Hartmann, T. 2000. Selective sequestration of pyrrolizidine alkaloids from diverse host plants by Longitarsus flea beetles (Coleoptera, Chrysomelidae). Journal of Chemical Ecology, 26 1281-1298. 

Fig. 7.4. Phytogeny of the Arctiidae (after Jacobson and Weller, 2001) showing the evolutionary interrelationship of larval pyrrolizidine alkaloid (PA) sequestration and adult pharmacophagous behavior. Node 1, larval PA detoxifica-tion/sequestration abilities evolve node 2, adult pharmacophagy originates.

Ehmke, A., Witte, L., Biller, A. and Hartmann, T. (1990). Sequestration, A-oxidation, and transformation of plant pyrrolizidine alkaloids by the arctiid moth Tyria jacobaeae... 

Wink, M. and von Nickisch-Rosenegk, E. (1997). Sequence data of mitochondrial 16S rDNA of arctiidae and nymphalidae evidence for a convergent evolution of pyrrolizidine alkaloid and cardiac glycoside sequestration. Journal of Chemical Ecology 23 1549-1568. 

Orr A. B., Trigo J. R., Witte L. and Hartmann T. (1996) Sequestration of pyrrolizidine alkaloids by larvae of Tellervo zoilus (Lepidoptera Ithomiinae) and their role in the chemical protection of adult against the spider Nephila maculata (Araneidae). Chemoecol. 7, 68-73. 

Trivers R. L. (1985) Social Evolution. Benjamin Cummings, Menlo Park, CA. von Nickisch-Rosenegk E. and Wink M. (1993) Sequestration of pyrrolizidine alkaloids in several arctiid moths (Lepidoptera Arctiidae). J. Chem. Ecol. 19, 1889-1903. Vasconcellos-Neto J. and Lewinsohn T. M. (1984) Discrimination and release of unpalatable butterflies by Nephila clavipes, a neotropical orb-weaving spider. Ecol. Entomol. 9, 337-344. 

A variant of this procedure that employs a substoichiometric quantity of cinchona alkaloid has also been developed by Bolm [176]. In this method, 10 mol% quinidine was used in conjunction with a stoichiometric amount of 1,2,2,6,6-pentamethylpiperidine (pempidine) to prevent sequestration of the cinchona alkaloid by the acidic hemiester product. The chiral hemiester products derived from various meso-anhydrides were obtained with >74% ee and >94% yields (Table 8.8). 

Not surprisingly, although the evolution of sequestered microbial toxins appears to be rather widespread in marine environments, sequestration of defensive alkaloids in the apparent absence of microorganisms may generally characterize the chemical defenses of terrestrial animals. Careful searches for possible microbial syntheses of defensive compounds (allomones) have not been generally implemented, but recent studies in a few laboratories raise the possibility that microbial endosymbionts may be of major importance in the biogenesis of selected insect deterrents. 

Sequestration of toxic alkaloids also has another benefit for the insects that feed on these forbidden fruits. In a very real sense these herbivores are conspicuously marked with colorful patterns that designate them as toxic animals. They are described as aposematic or warningly colored organisms, in much the... 

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