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In this study we conditioned fathead minnows (Pimephales promelas) to recognize the odor of a perch (Perca flavescens) by exposing them to perch odor coupled with minnow alarm cue. We then staged encounters between the predator and prey in order to assess whether the predator odor training had any effect on survival of the prey. We tested for a survival effect in the presence and absence of shelter. Our results indicate that fish trained with alarm signals to recognize predators gained a survival benefit during staged encounters with a predator and that habitat characteristics influenced the survival of conditioned fish.

A wide diversity of aquatic organisms release chemical alarm cues when captured by a predator. For most animals, it is not known whether the specific chemicals that comprise the alarm cue are conserved as prey animals age. In this study, we tested whether brook char (Salvelinus fontinalis) can differentiate alarm cues produced by individuals of different ages/sizes. In separate laboratory experiments we exposed small brook char and large brook char to chemical alarm cues from small brook char, large brook char, and a control of swordtails (Xiphophorus helleri). Both small and large brook char responded with antipredator behavior to chemical alarm cues from both small and large char, but not to those from swordtails. Small char responded with a greater response intensity to cues of small char than to cues of large char. In contrast, large char responded with a greater response intensity to cues of large char than to cues of small char. These results suggest that chemical(s) that act as the alarm cue for fish of different age/size classes may be: (1) identical and that there may be other chemical(s) that allow the test fish to distinguish between cues from fish of different ages/sizes, or (2) the cues are not identical, but similar enough to be recognized.

Larval red-legged frogs (Rana aurora) are known to exhibit antipredator behavior in response to both chemical alarm cues released from injured conspecifics and chemical cues of predators. In some cases, the response to predators is dependent on the predator's diet. In this experiment, we tested whether long-term exposure to predator chemical cues and alarm cues resulted in alteration of life history characteristics of red-legged frogs. We raised groups of tadpoles in the presence of chemical cues of predators that were either fed conspecifics or heterospecific caddis-fly larvae, chemical cues of injured conspecifics, or a no-cue control. Tadpoles raised in the presence of either a predator fed conspecifics or cues of injured conspecifics metamorphosed earlier and at a smaller size than those exposed to predators fed heterospecifics or the no-cue control. The result suggests that red-legged frogs exhibit a life history shift in response to predatory cues and that this response is dependent on the diet of predators.

A wide diversity of fishes possess chemical alarm signalling systems. However, it is not known whether the specific chemicals that act as alarm signals are conserved within most taxonomic groups. In this study we tested whether cross-species responses to chemical alarm signals occurred within salmonid fishes. In separate laboratory experiments, we exposed brook charr (Salvelinus fontinalis), brown trout (Salmo trutta), and rainbow trout (Oncorhynchus mykiss) to chemical alarm signals from each of the three salmonid species and from swordtails (Xiphophorus helleri). In each case, the test species responded with appropriate antipredator behavior to all three salmonids alarm cues, but did not react to swordtail cues. These data suggest that chemical alarm cues are partially conserved within the Family Salmonidae. For each species tested, the intensity of the response was stronger to conspecific alarm cues, than to heterospecific alarm cues, indicating that salmonids could distinguish between chemical cues of conspecifics versus heterospecifics. These results suggest that the chemical(s) that act as the alarm cues may be: 1) identical and that there may be other chemical(s) that allow the test fish to distinguish between conspecifics and heterospecifics, or 2) that the cues that act as signals are not identical, but are similar enough to be recognized.

Bullfrogs (Rana catesbeiana), native to eastern North America, were introduced into Oregon in the 1930's. Bullfrogs are highly efficient predators that are known to eat a variety of prey including other amphibians. In laboratory experiments, we investigated whether juvenile Pacific treefrogs (Hyla regilla) recognize adult bullfrogs as a predatory threat. The ability of prey animals to acquire recognition of an introduced predator has important implications for survival of the prey. We found that treefrogs from a population that co-occurred with bullfrogs showed a strong avoidance of chemical cues of bullfrogs. In contrast, treefrogs from a population that did not co-occur with bullfrogs, did not respond to the bullfrog cues. Additional experiments showed that both populations of treefrogs use chemical cues to mediate predation risk. Treefrogs from both populations avoided chemical alarm cues from injured conspecifics.

We examined the effects of predator diet on the antipredator responses of larval woodfrogs (Rana sylvatica). We found that tadpoles showed stronger responses to fish (Perca flavescens) that were fed tadpoles than those fed invertebrates. Similarly, we found that tadpoles responded more strongly to larval dragonflies (Anax spp.) fed tadpoles than to dragonflies fed invertebrates. The overall intensity of response of tadpoles to fish was much stronger than that to dragonflies. Predator diet effects are not ubiquitous in predator–prey systems. We discuss possible reasons why predator diet effects are seen in some, but not all, predator–prey systems.

Slimy sculpins (Cottus cognatus) are small benthic fish that commonly co-occur with predatory fishes throughout most of their range in North America. In two laboratory experiments we examined the nature and extent of responses of slimy sculpins to chemosensory cues from predatory brook trout (Salvelinus fontinalis) and chemical alarm cues released by conspecific sculpins. Sculpins responded to three different classes of chemical stimuli: (1) cues of predatory brook trout, (2) damage-released alarm cues from conspecific sculpins, and (3) disturbance cues from conspecific sculpins. Sculpins did not distinguish between trout fed different diets; however, the presence of damage-released alarm cues did enhance the intensity of response to the predator chemicals. A histological analysis of the skin of sculpins revealed the presence of large sacciform cells that may act as the source of chemical alarm signals.

Brook charr (Salvelinus fontinalis) lay their eggs in gravel nests called redds. The nests are not defended for extended periods and the eggs and young may be subject to predation from predators that travel through the substrate into the redd. In this study we tested whether long-term exposure of brook charr eggs to chemical cues from predatory sculpins (Cottus cognatus) resulted in an adaptive shift in the timing of emergence of charr alevins from artificial redds. We reared brook charr eggs in the presence of chemical cues from sculpins fed brook charr eggs, sculpins fed brine shrimp, and a well water control. Significantly more alevins emerged during the first week of the emergence period when exposed to chemical cues from sculpins fed eggs than from cues from sculpins fed brine shrimp or from well water. Alevins that emerged sooner were smaller and possessed larger yolk sacs than alevins that emerged later in the emergence period. Our results suggest that alevins that emerge sooner may escape predation in the redd, but may pay a cost in being under-developed upon emergence into the open water of the stream or lake.

Larvae of the mayfly Siphlonisca are predators of the detritivorous mayfly Siphlonurus in floodplain wetlands in Maine (USA). Both mayflies are natural prey of brook trout (Salvelinus fontinalis). We exposed larvae of Siphlonurus and Siphlonisca to chemicals from injured conspecifics and their predators. Significant decreases in movement activity by Siphlonurus were elicited by chemicals released from Siphlonisca, chemicals released from brook trout fed conspecifics, and by chemicals released from injured conspecifics. A significant decrease in movement activity by Siphlonisca was elicited by chemicals released from brook trout fed either conspecifics or Siphlonurus. Movement activity by either Siphlonurus or Siphlonisca was not significantly affected by chemicals released from trout feeding on brine shrimp (Artemia). Both Siphlonurus and Siphlonisca were able to detect chemicals that provided information about past feeding behaviour by brook trout. However, their response to the chemicals used in this study was context-specific. A reduction in movement activity, a behavior that presumably reduces the probability of being consumed by visual predators, occurred only when mayflies were exposed to chemicals released by brook trout feeding on conspecific (Siphlonurus) or confamilial (Siphlonisca) prey.

Larval western toads (Bufo boreas) are known to exhibit antipredator behavior in response to both chemical alarm cues released from injured conspecifics and chemical cues of predatory invertebrates. In this study, we tested whether long-term exposure to predator and alarm cues resulted in an adaptive shift in life history characteristics of the toads. We raised groups of tadpoles in the presence of: (1) predatory backswimmers (Notonecta spp.) that were fed toad tadpoles, (2) nonpredatory water boatman (Corixidae), and (3) chemical alarm cues of injured conspecifics. Tadpoles raised in the presence of both chemical alarm cues and cues of predators fed tadpoles metamorphosed in significantly shorter time than those raised in the presence of the nonpredator control. Reducing time taken to reach metamorphosis would reduce exposure to aquatic predators. There was no difference among treatments in the size at metamorphosis. Our results suggest that this shift in metamorphic characteristics may represent a facultative alteration in life history.

We exposed the freshwater amphipod Gammarus lacustris, to chemical stimuli from injured conspecifics and to chemical stimuli from two types of natural predators: dragonfly larvae (Aeshna eremita) and northern pike (Esox lucius). Exposure to all three stimuli caused G. lacustris to reduce significantly its level of activity relative to activity recorded in response to a distilled water control. The similarity in responses to chemicals associated with predators and to injured conspecifics suggests the presence of an alarm pheromone within the body tissues of G. lacustris. In response to chemical stimuli from pike, G. lacustris tended to reduce its time in the water column and spend more time near the bottom of the test aquaria. However, no such trend was apparent in response to chemical stimuli from dragonfly larvae. The differences in response to chemical stimuli from pike and larval dragonflies suggest that G. lacustris does not have a rigid behavioral response to predation risk; instead, antipredator behavior may be modified to maximize avoidance of predators that are active in different microhabitats.

We studied two populations of damselfly larvae (Enallagma boreale): one population cooccurred with a predatory fish (northern pike, Esox lucius); the other did not. Damselflies that cooccurred with pike adopted antipredator behavior (reduced activity) in response to chemical stimuli from injured conspecifics, and to chemical stimuli from pike, relative to a distilled water control. Damselflies from an area where pike do not occur responded only to chemical stimuli from injured conspecifics. In a second set of experiments, we conditioned pike-naive damselflies to recognize and respond to chemical stimuli from pike with antipredator behavior. Damselfly larvae that were previously unresponsive to pike stimuli learned to recognize pike stimuli after a single exposure to stimuli from pike and injured damselflies or pike and injured fathead minnows (Pimephales promelas). The response to injured fathead minnows was not a general response to injured fish because damselfly larvae did not respond to chemical stimuli from injured swordtails (Xiphophorus helleri), an allopatric fish. Taken together, these data suggest a flexible learning program that allows damselfly larvae to rapidly acquire the ability to recognize local predation risk based on chemical stimuli from predators, conspecifics, and heterospecific members of their prey guild.

Fathead minnows (Pimephales promelas) are able to detect conspecific alarm pheromone in the feces of northern pike (Esox lucius) and have been shown to avoid areas labeled with the feces of pike that were fed minnows. The minnows did not avoid areas labeled with the feces of pike that were fed swordtails (Xiphophorous helleri), which lack ostariophysan alarm pheromone. In laboratory experiments, pike fed a diet of minnows localized their defecation away from their foraging area. It has been suggested that in doing so, pike may remove chemical cues that label their foraging area as dangerous to prey species. As yet there has been no conclusive evidence to support this hypothesis. In this experiment, we test the effects of different predator diets on localized defecation by pike. Pike were fed minnows, swordtails, or mice (Mus musculus). Swordtails and mice lack ostariophysan alarm pheromones. Area use and location of feces were recorded. Pike fed minnows spent significantly more time in the home area (i.e., area of the test tank where they were fed) and defecated significantly more often in the opposite end of the tank. Pike fed swordtails also exhibited a significant preference for the home area in area use, while those fed mice showed no such preference. When fed either swordtails or mice, there was no significant difference between the proportion of time spent and proportion of feces in each area of the test tank. These data suggest that pike localize their defecation only when consuming prey items containing alarm pheromone. The current findings support the hypothesis that pike localize their defecation to remove chemical cues from the foraging area of the home range in order to avoid chemically labeling their foraging area as dangerous to prey.

The probability of prey avoiding a predator's attack should increase if the predator's presence is detected at an early stage in the predation sequence. In this study, we tested whether threatened Iowa darters (Etheostoma exile) release disturbance pheromones that warn conspecifics of the presence of predation threat. Pairs of aquaria were visually isolated from one another, but connected chemically by water circulating between them. Darters in one aquarium were observed before and after darters in the other aquarium were chased with a model predator. In control tests, the model was moved in the same manner but there were no darters in the upstream tank. Darters receiving water from threatened fish increased vigilance behavior and decreased movement. Vigilant fish raised their head above the substratum, propping themselves up on their pectoral fins and/or arching their neck dorsally, pointing the snout upward. Exposure to water from disturbed darters suppressed exploratory behavior and resulted in movement by short rapid hops that ended abruptly in a rigid, alert posture. This study suggests that Iowa darters release a disturbance pheromone that can provide conspecifics with an early warning of predation risk.

We conducted a predator bite survey on a population of fathead minnows (Pimephales promelas) considered to be under substantial predation pressure by western plains garter snakes (Thamnophis radix). Scarring, due to failed predation attempts by garter snakes and crayfish (Orconectes virilis), was observed significantly more often in breeding males than in breeding females and nonbreeding minnows. Likely, territorial nest defense under the edges of rocks along the water's edge, a habitat occupied by crayfish and frequented by snakes, caused the breeding males to be differentially vulnerable to predation. Under controlled laboratory conditions, breeding males from this population exhibited an antipredator response to chemical stimuli from live snakes (T. sirtalis andT. radix) significantly more often than breeding female minnows from the same population and breeding minnows of both sexes from a population that was presumed to be under lower predation pressure from snakes.

Larval red-legged frogs (Rana aurora) are known to exhibit antipredator behavior in response to both chemical alarm cues released from injured conspecifics and chemical cues of predators. In some cases, the response to predators is dependent on the predator's diet. In this experiment, we tested whether long-term exposure to predator chemical cues and alarm cues resulted in alteration of life history characteristics of red-legged frogs. We raised groups of tadpoles in the presence of chemical cues of predators that were either fed conspecifics or heterospecific caddis-fly larvae, chemical cues of injured conspecifics, or a no-cue control. Tadpoles raised in the presence of either a predator fed conspecifics or cues of injured conspecifics metamorphosed earlier and at a smaller size than those exposed to predators fed heterospecifics or the no-cue control. The result suggests that red-legged frogs exhibit a life history shift in response to predatory cues and that this response is dependent on the diet of predators.

A wide diversity of aquatic organisms release chemical alarm cues when captured by a predator. For most animals, it is not known whether the specific chemicals that comprise the alarm cue are conserved as prey animals age. In this study, we tested whether brook char (Salvelinus fontinalis) can differentiate alarm cues produced by individuals of different ages/sizes. In separate laboratory experiments we exposed small brook char and large brook char to chemical alarm cues from small brook char, large brook char, and a control of swordtails (Xiphophorus helleri). Both small and large brook char responded with antipredator behavior to chemical alarm cues from both small and large char, but not to those from swordtails. Small char responded with a greater response intensity to cues of small char than to cues of large char. In contrast, large char responded with a greater response intensity to cues of large char than to cues of small char. These results suggest that chemical(s) that act as the alarm cue for fish of different age/size classes may be: (1) identical and that there may be other chemical(s) that allow the test fish to distinguish between cues from fish of different ages/sizes, or (2) the cues are not identical, but similar enough to be recognized.

In this study we conditioned fathead minnows (Pimephales promelas) to recognize the odor of a perch (Perca flavescens) by exposing them to perch odor coupled with minnow alarm cue. We then staged encounters between the predator and prey in order to assess whether the predator odor training had any effect on survival of the prey. We tested for a survival effect in the presence and absence of shelter. Our results indicate that fish trained with alarm signals to recognize predators gained a survival benefit during staged encounters with a predator and that habitat characteristics influenced the survival of conditioned fish.

Brook stickleback (Culaea inconstans) share habitat and predators with cyprinid species, and they exploit the alarm pheromone of fathead minnows (Pimephales promelas) to avoid areas of high predation risk. In this field experiment, we measured the retention and duration of area avoidance by brook stickleback from areas marked with alarm pheromone of fathead minnows. Area avoidance was greatest during the first 2 hr after the source of the alarm pheromone was removed (P

Solitary fathead minnows (Pimephales promelas) were rendered anosmic and exposed to chemical stimuli from a predatory northern pike (Esox lucius) to determine the role of olfaction in the minnow's ability to recognize predators on the basis of chemical stimuli. Anosmic fish did not respond to the pike stimuli with a typical fright reaction, while control fish, with intact olfactory receptors, did. These results demonstrate that the olfactory system is necessary for the ability of fathead minnows to recognize northern pike as a predator and that the gustatory and single-celled chemosensory systems are not sufficient for this recognition in the absence of olfactory input. Olfactory impairment was behaviorally confirmed by exposing minnows to alarm substance (Schreckstoff).