Anti-predation chemicals

Lass S, Spaak P (2003) Chemically induced anti-predator defences in plankton a review. Hydro-biologia 491 221-239... 

Sakamoto M, Chang K-H, Hanazato T (2006) Inhibition of development of anti-predator morphology in the small cladoceran Bosmina by an insecticide impact of an anthropogenic chemical on prey-predator interactions. Freshw Biol 51 1974—1983... 

Mirza and Chivers (in press) found that fathead minnows had the ability to learn to recognize a novel heterospecific odour as an indication of predation if the cue was present in the diet of a known predator. In their study, minnows were exposed to chemical stimuli collected from a tank containing a known predator (northern pike, Esox lucius) fed one of two unknown prey, stickleback or swordtails (Xiphophorous helleri). In subsequent behavioural tests, the minnows were exposed to either swordtail skin extract or stickleback skin extract. Minnows exposed to the odour of pike fed stickleback responded to stickleback skin extract with an anti-predator response but did not respond to swordtail skin extract. Similarly, minnows exposed to pike fed swordtail cues responded to swordtail skin extract with an antipredator response but did not respond to stickleback skin extract. This study demonstrated that minnows had the ability to learn to recognize a novel cue in the diet of a known predator, whether that cue is from a species that commonly co-occurs with minnows (the stickleback) or an allopatric tropical species with which it has never co-occurred. 

Chivers et al. (2002) tested whether or not learned responses could result in a survival benefit, besides confirming that fish could learn unknown heterospecific cues through the diet or a predator. In a two-part study, fathead minnows were exposed to chemical stimuli collected from rainbow trout (Oncorhynchus mykiss) fed a mixed diet of either minnows and brook stickleback, or swordtail and stickleback. To test if the minnows had acquired recognition of stickleback alarm cues, Chivers et al. (2003) exposed the fish to stickleback alarm cues and introduced an unknown predator, yellow perch or northern pike. Both perch and pike took longer to initiate an attack on minnows that were previously exposed to trout fed minnows and stickleback than those previously exposed to trout fed swordtails and stickleback. These results show again that fishes are able to learn novel cues through association with known cues in a predator s diet. Furthermore, it shows that anti-predator responses to these newly learned cues could result in a survival benefit. 

Most laboratory studies examining the responses of fishes to chemical alarm cues have shown that the anti-predator responses exhibited to conspecific cues are specific to conspecifics and are not generalized responses to any injured fish cue or any novel odor (Chivers and Smith, 1998). Consequently, most of the field tests have used distilled water as the control. However, more recently, several studies now include an unfamiliar heterospecific skin extract (usually swordtail, Xiphophorus helleri) or novel odors, such as morpholine, as additional controls. In some cases the results are somewhat surprising. 

Shoal membership reduces a predator s ability to visually isolate individual prey, and allows fellow prey to act as shields against direct attack (Wisenden et al., in press). Therefore, the presence of conspecific shoals, or shoals of ecologically or morphologically similar heterospecifics are attractive to prey species. A trap experiment conducted by Wisenden et al. (in press) investigated the interaction between the presence of fish shoals (held within a transparent jar) and chemical alarm cues. The presence of chemical alarm cues alone caused prey to avoid traps, while the presence of a fish shoal alone attracted fish to traps. When chemical alarm cues were combined with the presence of a shoal, fish tended to increase shoal cohesion and enter the traps, despite the fact that the traps were the source of the alarm cue. An understanding of the interaction between visual and chemical cues is critical in the evaluation of anti-predator behavior of natural populations of fishes. 

Field studies are necessary to validate anti-predator responses of prey fishes in the chemically complex natural environment. While several of the early trap experiments demonstrated the effectiveness of alarm cues in the field (i.e., Mathis and Smith, 1992), the more complicated recent studies often demonstrate no preferential avoidance between familiar and unfamiliar cues or, alternatively, results are contradictory to predictions. Trap experiments have therefore brought into question previous knowledge based primarily on laboratory studies (i.e., visual compensation model). Anti-predator defense strategies of fishes are clearly context-dependent. To decipher and explore the complexities of this dependent response further, field studies investigating the various biotic and abiotic factors affecting a fish s response are required. 

Anti-predator adaptations are often mediated or induced by chemical cues (Kats and Dill, 1998), especially in aquatic systems where visual cues are limited (Smith, 1992). Chemical cues function well in this medium as a large number of compounds can dissolve in water allowing for the production of a great number of possible signals (Hara, 1994). Research, in the past decade, has indicated that the assessment of these chemical cues is highly sophisticated (reviews Chivers and Mirza, 2001). Logically, the ability to accurately assess the risk of predation would be beneficial as each anti-predator defense has an innate cost to the user and the effectiveness of each response option is dependent on the context of the encounter and the specific predator. 

Madison, D. M., Sullivan, A. S., Maerz, J. C., McDarby, J. H., and Rohr, J.R., 2002, A complex, cross-taxon, chemical teleaser of anti-predator behavior in amphibians, J. Chem. Ecol. 28 2271-2282. 

Sullivan, A. M., Maerz, J. C., and Madison D. M., 2002, Anti-predator response of red-backed sakunanders (Plethodon cinereus) to chemical cues fiom garter snakes (Thamnophis sirtalis) laboratory and field experiments. Behav. Ecol. Sociobiol. 51 227-233. 

Many organisms rely on anti-predator defenses after contact with a predator (Brodie, Formanowicz Brodie, 1991). Because energetic costs and mortality risks are increased during contact, some species avoid these interactions whenever possible. A number of animals chemically detect and avoid predators, including invertebrates (Parker Shulman, 1986 Alexander Covich, 1991 Turner, 1996), fish (Keefe, 1992 Smith, 1992 Mathis Smith, 1993), reptiles (Thoen, Bauwens Verheyen, 1986 Dial, 1989 Cooper, 1990), and mammals (Weldon, 1990). In anuran amphibians, tadpoles commonly avoid the waterborne odors of predators (Petranka, Kats Sih, 1987 Flowers Graves, 1997 Kie-secker, Chi vers Blaustein, 1997), and among caudate amphibians, both larval and adult... 

In summary, we believe our experiments indicate that red-backed salamanders identify and avoid chemical substances deposited by spotted salamanders and garter snakes, and since the latter two species are either known or probable predators of red-backed salamanders, we believe the avoidance response is an anti-predator mechanism that decreases predation risk. 

A recent example demonstrates that corals rely on induced biosynthesis of terpenes as a dynamic defense strategy as well. The induction of terpenoid secondary metabolites was observed in the sea whip Pseudopterogorgia elisabethae [162]. Levels of pseudopterosins 89-92, a group of diterpene glycosides with anti-inflammatory and analgesic properties (Scheme 23) [163-165], are increased in response predation by the mollusk Cyphoma gibbosum. First bioassays indicate that these natural products are involved in the chemical defense. 

Polyphenols are considered secondary metabolites of plants involved in the chemical defense of plants against predators and in plant-plant interactions. Polyphenols are found in virtually all families of plants, and comprise up to 50% of the dry weight of leaves. The main activity related to phenolic compounds is antioxidant activity. In addition to their strong antioxidant activities, plant polyphenols are known to possess other activities including antibacterial, chemopreventive, UV-protective, anticancer, and anti-inflammatory effects, act as detoxifying agents against heavy metals, and have myriad other bioactivities that could potentially be exploited for application in functional foods. ... 

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