Feeding cues

The assays described above assess how foragers use compounds to detect and move toward prey. Once prey have been encountered, feeding stimulants or deterrents affect the probability that prey will actually be consumed. Large numbers of investigations have demonstrated, in both field and laboratory assays, that secondary metabolites from seaweeds and benthic invertebrates serve as deterrents to feeding by marine consumers (reviewed by Hay Fenical 1988  

Many of the early investigations of prey chemical defenses were conducted by placing potential consumers into water containing secondary metabolites that had been extracted from potential prey. These assays lacked ecological realism in that (1) many of these compounds are not naturally leached into seawater (2) if they were, they would disperse rapidly and not be present at significant concentrations and (3) the potential predators would not normally encounter the 

The types of bioassays suggested above can be conducted at ecologically realistic concentrations by placing crude extracts or fractions into test foods at the same concentration per food dry mass or per volume (if test foods mimic prey in nutritional value per volume) that occurs in the organisms from which they were extracted. For this to be valid, the nutritional quality of the test food should approximate the nutritional value of the organism from which the extract was obtained. 

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Highly toxic substances, such as cyanides, are sometimes feeding cues and stimulants for specialized insects. For example, instar larvae of the southern armyworm (Spodoptera eridania) strongly prefer cyanogenic foods, such as foliage of the lima bean, a plant with comparatively elevated cyanide content — up to 31 mg/kg in some varieties — in the form of linamurin (Brattsten et al. 1983). Feeding was stimulated in southern army worms at dietary levels up to 508 mg KCN/kg... 

B Tannins were consulted but nevertheless they were negative feeding cues. E Tannins may well have contributed to nutrient stress at a time when high martality occurred. Tannins in feces indicated their ability to pass through the gut unaltered. 

B Foods low in tannins selected, but fibre is major negative feeding cue. 

Adult zebrafish generally exhibit a clear attractive response to amino acids, recognizing them as potential feeding cues (Steele et al. 1990, 1991), although an... 

Nucleotides such as ATP, IMP, and ITP induce excitatory responses in a subpopulation of fish OSNs and bulbar neurons (Kang and Caprio 1995 Nikonov and Caprio 2001), possibly acting as feeding cues (Carr 1988). They activate glomeruli located in the lateral portion of the OB that partly overlaps with the amino acid... 

In terms of function, condensed tannins apparently act mainly against the action of microbes, whereas hydrolyzable tannins defend primarily against chewing phytophagous insects or animals (Lewis and Yamamoto, 1989). Because tannins bind salivary proteins, most tannins are astringent to mammals. Many insects, as well as other animals, avoid plants rich in tannins. On the other hand, tannins may also serve as phagostimulants and feeding cues (Schultz, 1989). 

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