Prey capture toxins

The toxins identified from cone snails, nemerteans, cephalopod molluscs, etc. undoubtedly play some role in prey capture, but their importance relative to other predatory behaviors is generally unknown. For some predators, toxins may serve as a secondary rather than primary mode of... 

It is currently unclear whether toxin-mediated prey capture by mobile invertebrates has a significant impact on prey population size or community composition. In freshwater systems, chemically mediated prey capture by flatworms has been demonstrated to significantly impact prey populations in the laboratory. Neurotoxic chemicals released from the mucus webs of the flatworm Mesostoma can drive entire populations of the cladoceran Daphnia magna to extinction in culture, but the concentration these chemicals normally attain under realistic field conditions is unknown. Nevertheless, because the mucus webs these flatworms build function to trap prey, Dumont and Carels163 likened these flatworms to spiders with toxic webs. Similar impacts may occur in open water marine systems where organisms that employ toxin-mediated prey capture are abundant, or even dominant, predators (e.g., chaetognaths and cnidarians). 

Six a-conotoxins have been isolated from C. geographus, two of which target the neuronal nAChRs, suggesting that both muscle and neuronal subtypes are important in prey capture. Often multiple a3/5-conotoxins are found within the venom of one mollusk, although the reason for having multiple toxins targeting one receptor is not clear. 

Long-term assays Toxin-mediated prey capture... 

The mechanisms of envenomation are not always known. For example, early accounts of prey capture by octopi claimed that crabs were killed when the octopi released toxins into the water without the need of biting the prey. Later studies, however, failed to show envenomation by toxins dissolved in the water (see references in Wells 1978). Other studies have shown that crabs trapped by an octopus (Eledone spp.) exhibited signs of paralysis before the octopus had time to drill through the carapace of the crab (see references in Hanlon Messenger 1996), but the site of entry for the toxin remains unknown. 

Cnidarians pose a particularly difficult challenge. The toxins produced by jellyfish and some hydrozoans are among the most powerful known, and have been relatively well characterized (Russell 1984). However, because the toxins are delivered through diverse kinds of nematocysts, experimental manipulations may be difficult. The role of toxins in prey capture has been inferred from the isolation of nematocyst-associated toxins, the behavior of exposed prey, and... 

As guidelines, we suggest that researchers interested in the ecology of toxins as means of prey capture consider the following ... 

One of the most extensively studied families of peptide toxins, the conotoxins, is isolated from marine cone snails.140 141 Each snail produces a suite of 100-200 peptides in its venom, which is used for the capture of prey, and given that more than 500 species of cone snails are thought to exist, conotoxins represent an enormous diversity of peptide toxins. They have been classified into families, based on their target receptor specificity, and superfamilies, according to their... 

If toxins are used to capture food, then the presence of the toxin in the prey tissues should be confirmed once prey have been attacked. No studies have assayed for the presence of metabolites from the attackers inside the prey, even in cases where the toxins are known. 

The phylum Coelenterata is subdivided into the classes Hydrozoa, Cubozoa, Scyphozoa, and Anthozoa. The latter class is subdivided into Hexa- and Octocorallia. Many coelenterates produce toxic or other biologically active metabolites 235). For example toxins are used by jellyfish and sea anemones for defence or in order to capture prey. 

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