The Effects of Density on the Learned Recognition of Heterospecific Alarm Cues

Numerous species, both aquatic and terrestrial, use alarm cues to mediate predation risk. These cues may be either intentionally or inadvertently released, and may be received by either conspecifics or heterospecifics. In aquatic systems, alarm cues are often chemical in nature and are released when an organism is disturbed or damaged by a predator. In some cases the recognition of alarm cues from conspecifics, or closely related heterospecifics, is innate, while the recognition of alarm cues from distantly related species must be learned. Many studies have documented the use of heterospecific alarm cues, but few have explored the manner in which these cues come to be recognized as an indication of predation. In the current study, we examined the fathead minnow (Pimephales promelas)/brook stickleback (Culaea inconstans) alarm system. We tested the effect of density on the ability of minnows to learn to recognize stickleback alarm cues as a threat. We hypothesized that the ability of minnows to learn to recognize stickleback alarm cues should increase with increasing stickleback density because there would be more opportunity for minnows to associate the heterospecific alarm cue with the threat. To test this hypothesis we stocked minnows into large outdoor pools with no stickleback, low numbers of stickleback, or high numbers of stickleback. All pools contained a predator (pike, Esox lucius) known to the minnows. Following a 14 d conditioning period, minnows were tested for a response to skin extract from stickleback, minnow, and an unknown heterospecific (swordtail, Xiphophorus helleri). Minnows from pools with large numbers of stickleback learned to respond to stickleback alarm cues while minnows from pools with low numbers of stickleback, or no stickleback, did not.     

Fathead Minnows, Pimephales promelas, Learn to Recognize Chemical Alarm Cues of Introduced Brook Stickleback, Culaea inconstans

In four experiments conducted over a 6-year period, we investigated whether fathead minnows, Pimephales promelas, could acquire the ability to recognize chemical alarm cues of introduced brook stickleback, Culaea inconstans. A laboratory experiment documented that stickleback-naïve minnows did not exhibit an anti-predator response when exposed to the chemical alarm cues of stickleback. In a laboratory experiment conducted 5 years after the introduction of stickleback to the pond, minnows exhibited an antipredator response to stickleback cues. Moreover, in a field experiment the minnows exhibited avoidance of areas labelled with stickleback alarm cues. Minnows raised from eggs taken from the test pond did not exhibit an anti-predator response to stickleback cues while minnows from the test pond that had experience with stickleback cues did respond to stickleback cues. Our results provide clear evidence that cross-species responses to chemical alarm cues of fishes can be learned. Learned recognition of alarm cues has important implications for predator/prey interactions.     

Underwater Video Reveals Strong Avoidance of Chemical Alarm Cues by Prey Fishes

A diversity of fishes release chemical cues upon being attacked by a predator. These cues, commonly termed alarm cues, act as sources of public information warning conspecifics of predation risk. Species which are members of the same prey guild (i.e. syntopic and share predators) often respond to one another's alarm cues. The purpose of this study was to discriminate avoidance responses of fishes to conspecific alarm cues and cues of other prey guild members from responses to unknown damaged fish odours and novel odours. We used underwater video to measure avoidance responses of freshwater littoral species, namely fathead minnows (Pimephales promelas), finescale dace (Chrosomus neogaeus), and brook stickleback (Culaea inconstans), to both injured fish cues and novel non‐fish odours. The cyprinids (minnows and dace) showed significant avoidance of minnow cues over swordtail cues, morpholine, and the control of distilled water and tended to avoid fathead cues over cues of known prey guild members (stickleback). Cyprinids also significantly avoided cues of stickleback over unknown heterospecific cues (swordtail) and tended to avoid stickleback cues over morpholine and the distilled water control. Stickleback significantly avoided fathead minnow extract over the distilled water and tended to avoid stickleback and swordtail over distilled water. We conclude that fishes in their natural environment can show dramatic changes in behaviour upon exposure to alarm cues from conspecifics and prey guild members. These responses do not represent avoidance of cues of any injured fish or any novel odour.     

Acquired Recognition of Chemical Stimuli from Pike,Esox lucius,by Brook Sticklebacks,Culaea inconstans (Osteichthyes,Gasterosteidae)

In this study we test whether brook sticklebacks (Culaea inconstans) can acquire predator recognition through releaser-induced recognition learning, i.e. simultaneous exposure to aversive ('releasing') stimuli and neutral stimuli causing learned aversion to the neutral stimuli. We exposed wild-caught pike-naive brook sticklebacks (collected from a creek containing fathead minnows, Pimephales promelas, but not pike, Esox lucius) to chemical stimuli from pike that were mixed with brook stickleback skin extract, fathead minnow skin extract, or a control of distilled water. In subsequent tests 2 d later, when only pike stimuli were presented, sticklebacks conditioned with stickleback skin extract and fathead minnow skin extract exhibited antipredator behaviour (i.e. increased schooling and movement toward the substrate), while those conditioned with distilled water did not. Sticklebacks conditioned with stickleback skin extract responded to pike with a more intense response, in terms of movement toward the substrate, than those conditioned with fathead minnow skin extract, suggesting that conspecific skin extract may be a stronger stimulus than heterospecific skin extract for learning recognition of predators. To our knowledge this is the first study to demonstrate that an acanthopterygian fish can acquire predator recognition through the pairing of conspecific alarm pheromone with the cue of a predator. Furthermore, our results are the first to demonstrate that fish can acquire predator recognition through the pairing of a heterospecific alarm pheromone with the cue of a predator. These results suggest that brook sticklebacks will benefit by being in close proximity to fathead minnows. Acquired predator recognition has long-term consequences in mediating predator-prey interactions.     

Chemically mediated predator inspection behaviour in the absence of predator visual cues by a characin fish

Animals commonly approach (i.e. 'inspect') potential predators. Glowlight tetras, Hemigrammus erythrozonus, have previously been shown to inspect the combined chemical and visual cues originating from novel predators and to modify their inspection (approach) behaviour depending upon the predator's diet. We conducted two experiments to determine whether tetras would inspect the chemical cues of injured prey or the dietary cues of a novel predator in the absence of any visual cues. Shoals of glowlight tetras were exposed to either distilled water (control) or the skin extract of swordtail (lacking ostariophysan alarm pheromones) or the skin extract of tetra (with alarm pheromones). There was no significant difference in the frequency of predator inspection behaviour towards swordtail or tetra skin extract compared to the distilled water controls. In the second experiment, we exposed shoals of tetras to either distilled water or the odour of Jack Dempsey cichlids, Cichlasoma octofasciatum, which had been food deprived, or fed a diet of swordtails or tetras. There was no significant difference in the frequency of predator inspection behaviour towards the odour of the starved cichlids and the odour of the fed cichlids in either of the two diet treatments. However, when tetras were exposed to the odour of cichlids fed tetras, they took significantly longer to initiate an inspection visit, remained further from the source of the chemical cues and inspected in smaller groups, compared with the odour of a starved cichlid or a cichlid fed swordtails. These data strongly suggest that tetras will inspect chemical cues alone, but only if the cue contains information about the predator. Copyright 2000 The Association for the Study of Animal Behaviour.     

Assessment of Predation Risk by Juvenile Yellow Perch, Perca flavescens: Responses to Alarm Cues from Conspecifics and Prey Guild Members

In two laboratory experiments we tested juvenile yellow perch, Perca flavescens, for behavioural responses to alarm cues of injured conspecifics and several prey guild members: adult perch, Iowa darters, Etheostoma exile and spottail shiners, Notropis hudsonius. Spottail shiners are phylogenetically distant to yellow perch whereas Iowa darters and perch are both members of the Family Percidae. Groups of juvenile yellow perch increased shoal cohesion and movement towards the substrate after detecting conspecific alarm cues when compared to cues of injured swordtails, Xiphophorus helleri, a species phylogenetically distant from perch. Individual juvenile perch increased shelter use and froze more when exposed to chemical alarm cues from both juvenile and adult perch, shiners and darters compared to exposure to injured swordtail cues or distilled water. The response to cues of darters may indicate that alarm cues are evolutionarily conserved within percid fishes or that perch had learned to recognize darter cues. The response to spot tail shiners likely represents learned recognition of the cues of a prey guild member.     

Chemical Predator Inspection in a Characin Fish (Hemigrammus erythrozonus, Characidae, Ostariophysi): The Effects of Mixed Predator Diets

Many prey organisms will approach (inspect) potential predators, primarily to assess local risk of predation. It has been demonstrated that Ostariphysan prey fishes can detect conspecific alarm pheromones in the diet of potential predators and use this chemical information to reduce their risk of predation while still gaining significant benefits associated with predator inspection. We conducted the current study to examine the possible effects of mixed diets on the use of these chemical predator diet cues during inspection visits. Shoals of four glowlight tetras ( Hemigrammus erythrozonus ) were exposed to Jack Dempsey cichlids ( Cichlasoma octofaciatum ) which had been fed diets consisting of: 100% tetras (with alarm pheromone); 75% tetra, 25% swordtail ( Xiphophorus helleri , which lack a recognizable alarm pheromone); 25% tetra, 75% swordtail; or 100% swordtails. Tetras significantly increased their anti-predator behaviour in response to predators fed 100% tetra or the two mixed predator diets, but not when exposed to predators fed a 100% swordtail diet. Likewise, we observed significant differences in inspection behaviour. Tetras took longer to initiate an inspection, inspected in smaller groups and directed a greater proportion of inspection visits towards the tail region of the predator when it had been fed 100% tetra or either of the two mixed prey diets. We found no significant differences in either anti-predator or inspection behaviour among the three diet treatments containing tetras. These data strongly suggest that glowlight tetras are capable of detecting relatively small amounts of conspecific alarm pheromone in the diet of potential predators and that they modify their behaviour based on the presence or absence of these cues.     

Influence of Body Size on the Responses of Fathead Minnows, Pimephales promelas, to Damselfly Alarm Cues

A wide diversity of aquatic organisms release chemical alarm cues upon encountering or being attacked by a predator. These alarm cues can be used by nearby individuals to assess local predation risk. Receivers warned by chemical alarm cues gain a survival benefit when encountering predators. Animals that are in the same prey guild (i.e. that co‐occur and share the same predators) may learn to recognize each others’ chemical alarm cues. This ability may confer an adaptive advantage if the prey animals are vulnerable to the same predators. However, if the prey grow to different sizes and as a consequence are no longer vulnerable to the same suite of predators, then there should no longer be an advantage for the prey to respond to each others’ alarm cues. In this study, we exposed small and large fathead minnows (Pimephales promelas) to cues from syntopic injured damselfly larvae (Enallagma boreale), cues from injured mealworm larvae (Tenebrio molitor) and to distilled water. Small minnows exhibited antipredatory behaviour and increased shelter use in response to injured damselfly cues but not to the controls of injured mealworm or distilled water. On the contrary, large minnows exhibited no significant change in shelter use in response to any of the injured cues. These data demonstrate that fathead minnows exhibit an antipredator response to damselfly alarm cues, but only when minnows are small and members of the same prey guild as damselfly larvae. These results demonstrate the considerable flexibility in the responses to heterospecific alarm cues.     

Chemical Recognition of Risky Habitats is Culturally Transmitted among Fathead Minnows,Pimephales promelas (Osteichthyes,Cyprinidae)

Fathead minnows (Pimephales promelas) have an alarm substance (AS), or 'Schreckstoff', in epidermal club cells. Mechanical damage to the skin, as caused by a predator attack, releases the AS. The area in which conspecifics detect AS may be considered dangerous or risky because of the high probability of a subsequent predator attack. We exposed fathead minnows to water from one of two habitats (an open-water site and a vegetated-cover site) that we mixed with either AS or a distilled water control. Upon subsequent exposure to water from these habitats alone, minnows showed an antipredator response to the water they experienced in conjunction with AS, but not to water they received in conjunction with the distilled water control. These results confirmed that minnows can be conditioned with AS to recognize chemical cues from high-risk habitats. Naive minnows present during the fright response of conditioned minnows also exhibited antipredator behaviour, and subsequently responded when tested alone. Our results demonstrate that learned recognition of high-risk habitats can be transmitted culturally, which may allow minnows to lower their risk of predation.     

Foraging Trade-offs in Fathead Minnows (Pimephales promelas,Osteichthyes, Cyprinidae): Acquired Predator Recognition in the Absence of an Alarm Response

Pike-naive fathead minnows (Pimephales promelas) were fed ad libitum or deprived of food for 12, 24, or 48 h and then exposed to either conspecific alarm pheromone or distilled water and the odour of a predatory northern pike (Esox lucius). Minnows fed ad libitum or deprived for 12 h showed a stereotypic alarm response to the alarm pheromone (increased time under cover objects and increased occurrence of dashing and freezing behaviour); those deprived of food for 24 h showed a significantly reduced alarm response, while those deprived of food for 48 h did not differ significantly from the minnows exposed to a distilled water control. Upon subsequent testing in an Opto-Varimex activity meter, all groups initially exposed to alarm pheromone and pike odour exhibited an alarm response when exposed to pike odour alone. Those initially conditioned with distilled water and pike odour did nor show an alarm response to pike odour alone. These results demonstrate that there exists a significant trade-off between hunger level and predator-avoidance behaviour in fathead minnows and that minnows can learn the chemical cues of a predatory northern pike through association with alarm pheromone even in the absence of an observable alarm response.     

Predator Inspection Behaviour in a Characin Fish: an Interaction between Chemical and Visual Information?

Recent evidence suggests that predator inspection behaviour by Ostariophysan prey fishes is regulated by both the chemical and visual cues of potential predators. In laboratory trials, we assessed the relative importance of chemical and visual information during inspection visits by varying both ambient light (visual cues) and predator odour (chemical cues) in a 2 × 2 experimental design. Shoals of glowlight tetras (Hemigrammus erythrozonus) were exposed to a live convict cichlid (Archocentrus nigrofasciatus) predator under low (3 lux) or high (50 lux) light levels and in the presence of the odour of a cichild fed tetras (with an alarm cue) or swordtails (Xiphophorus helleri, with an alarm cue not recognized by tetras). Tetras exhibited threat‐sensitive inspection behaviour (increased latency to inspect, reduced frequency of inspection, smaller inspecting group sizes and increased minimum approach distance) towards a predator paired with a tetra‐fed diet cue, regardless of light levels. Similar threat‐sensitive inspection patterns were observed towards cichlids paired with a swordtail‐fed diet cue only under high light conditions. Our data suggest that chemical cues in the form of prey alarm cues in the diet of the predator, are the primary source of information regarding local predation risk during inspection behaviour, and that visual cues are used when chemical information is unavailable or ambiguous.     

Fathead minnows avoid conspedfic and heterospedfic alarm pheromones in the faeces of northern pike

Groups of fathead minnows Pimephales promelas were tested to determine if they avoided areas of a test tank labelled with the faeces of a predator (northern pike, Esox lucius ) which had recently been fed minnows, brook sticklebacks Culaea inconstans , or swordtails Xiphophorus helleri. Minnows exhibited a fright reaction upon presentation of sponges labelled with faeces, when the pike had consumed minnows or sticklebacks, but not swordtails (which lack alarm pheromones). The fright reaction was characterized by increased shoal cohesiveness and increased dashing and freezing behaviour. Minnows avoided the area of the tank containing the faeces from pike on diets of minnows or sticklebacks, but not from pike fed a diet of swordtails. These data demonstrate that: (1) minnows actively avoid the faeces of pike fed minnows or brook sticklebacks, and (2) minnows exhibit a fright reaction to the faeces of a pike fed brook sticklebacks.     

Learned Recognition of Intraspecific Predators in Larval Long-Toed Salamanders Ambystoma macrodactylum

The ability of prey to detect predators and respond accordingly is critical to their survival. The use of chemical cues by animals in predator detection has been widely documented. In many cases, predator recognition is facilitated by the release of alarm cues from conspecific victims. Alarm cues elicit anti‐predator behavior in many species, which can reduce their risk of being attacked. It has been previously demonstrated that adult long‐toed salamanders, Ambystoma macrodactylum, exhibit an alarm response to chemical cues from injured conspecifics. However, whether this response exists in the larval stage of this species and whether it is an innate or a learned condition is unknown. In the current study, we examined the alarm response of naïve (i.e. lab‐reared) larval long‐toed salamanders. We conducted a series of behavioral trials during which we quantified the level of activity and spatial avoidance of hungry and satiated focal larvae to water conditioned by an injured conspecific, a cannibal that had recently been fed a conspecific or a non‐cannibal that was recently fed a diet of Tubifex worms. Focal larvae neither reduced their activity nor spatially avoided the area of the stimulus in either treatment when satiated, and exhibited increased activity towards the cannibal stimulus when hungry. We regard this latter behavior as a feeding response. Together these results suggest that an anti‐predator response to injured conspecifics and to cannibalistic conspecifics is absent in naïve larvae. Previous studies have shown that experienced wild captured salamanders do show a response to cannibalistic conspecifics. Therefore, we conducted an additional experiment examining whether larvae can learn to exhibit anti‐predator behavior in response to cues from cannibalized conspecifics. We exposed larvae to visual, chemical and tactile cues of stimulus animals that were actively foraging on conspecifics (experienced) or a diet of Tubifex (naïve treatment). In subsequent behavioral treatments, experienced larvae significantly reduced their activity compared to naive larvae in response to chemical cues of cannibals that had recently consumed conspecifics. We suggest that this behavior is a response to alarm cues released by consumed conspecifics that may have labeled the cannibal. Furthermore, over time, interactions with cannibals may cause potential prey larvae to learn to avoid cannibals regardless of their recent diet.     

Can prey exhibit threat-sensitive generalization of predator recognition? Extending the Predator Recognition Continuum Hypothesis

Despite the importance of predator recognition in mediating predator-prey interactions, we know little about the specific characteristics that prey use to distinguish predators from non-predators. Recent experiments indicate that some prey who do not innately recognize specific predators as threats have the ability to display antipredator responses upon their first encounter with those predators if they are similar to predators that the prey has recently learned to recognize. The purpose of our present experiment is to test whether this generalization of predator recognition is dependent on the level of risk associated with the known predator. We conditioned fathead minnows to chemically recognize brown trout either as a high or low threat and then tested the minnows for their responses to brown trout, rainbow trout (closely related predator) or yellow perch (distantly related predator). When the brown trout represents a high-risk predator, minnows show an antipredator response to the odour of brown trout and rainbow trout but not to yellow perch. However, when the brown trout represents a low-risk predator, minnows display antipredator responses to brown trout, but not to the rainbow trout or yellow perch. We discuss these results in the context of the Predator Recognition Continuum Hypothesis.     

Chemical Alarm Signals Enhance Survival of Brook Charr (Salvelinus fontinalis) During Encounters with Predatory Chain Pickerel (Esox niger)

A diversity of aquatic organisms release chemical alarm signals when attacked or captured by a predator. These alarm signals are thought to warn other conspecifics of danger and, consequently, may benefit receivers by increasing their survival. Here we experimentally investigated the differences in behaviour and survival of hatchery-reared juvenile brook charr Salvelinus fontinalis that had been exposed to either brook charr skin extract (experimental treatment) or a control of swordtail skin extract (control treatment). Charr exposed to conspecific skin extract exhibited a significant reduction in movement and/or altered their foraging behaviour in the laboratory when compared with charr exposed to swordtail skin extract. We also exposed charr to either water conditioned by a single brook charr disturbed by a predatory bird model or water conditioned by a single undisturbed brook charr. Charr exposed to disturbance signals reduced activity significantly more than charr exposed to chemical stimuli from undisturbed charr. These results demonstrate the existence of both damage-released alarm signals and disturbance signals in brook charr. Wild brook charr also responded to damage-released alarm cues under natural conditions. Charr avoided areas of a stream with minnow traps labelled with conspecific alarm cues vs. control cues. During staged encounters with chain pickerel Esox niger in the laboratory, predator-naive charr fry were better able to evade the predator if they were previously warned by an alarm signal, thus suggesting a survival benefit to receivers. Collectively, these results demonstrate that the presence of alarm signals in brook charr has important implications for understanding predator–prey interactions.     

Sound the alarm: learned association of predation risk with novel auditory stimuli by fathead minnows ( Pimephales promelas ) and glowlight tetras ( Hemigrammus erythrozonus ) after single simultaneous pairings with conspecific chemical alarm cues

Fathead minnows, Pimephales promelas, and glowlight tetras, Hemigrammus erythrozonus, were tested for their ability to associate predation risk with novel auditory stimuli after auditory stimuli were presented simultaneously with chemical alarm cues. Minnows and tetras gave a fright response when exposed to skin extract (alarm cue) and an artificial auditory sound stimulus, but no response to water (control) and sound, indicating that they did not have a pre-existing aversion to the auditory stimulus. When retested with sound stimuli alone, minnows and glowlight tetras that had previously been conditioned with water and sound showed no response, but those that had been conditioned with alarm cues and sound exhibited antipredator behaviour (reduced activity) in response to the auditory cue. This is the first known demonstration of learned association of an auditory cue with predation risk, and raises questions about the role of sound in mediating predator-prey interactions in fishes.     

The role of experience and chemical alarm signalling in predator recognition by fathead minnows, Pimephales promelas

Young-of-the-year, predator-naive fathead minnows, Pimephales promelas , from a pikesympatric population did not respond to chemical stimuli from northern pike, Esox Indus , while wild-caught fish of the same age and size did. These results suggest that chemical predator recognition is a result of previous experience and not genetic factors, Wild young-of-the-year minnows responded to pike odour with a response intensity that was similar to that of older fish, demonstrating that the ability to recognize predators is learned within the first year. The intensity of response of wild minnows which had been maintained in a predator free environment for 1 year was similar to that of recently caught minnows of the same age, suggesting that reinforcement was not required for predator recognition to be retained. Naive minnows that were exposed simultaneously to chemical stimuli from pike (a neutral stimulus) and minnow alarm substance exhibited a fright response upon subsequent exposure to the pike stimulus alone. Predator-naive minnows exposed simultaneously to chemical stimuli from pike and glass-distilled water did not exhibit a fright response to the pike stimulus alone. These results demonstrate that fathead minnows can acquire predator recognition through releaserinduced recognition learning, thus confirming a known mechanism through which alarm substance may benefit the receivers of an alarm signal.     

Motion, not Shape, Facilitates Association of Predation Risk with Novel Objects by Fathead Minnows (Pimephales promelas)

Injury‐released chemical cues are reliable indicators of predation risk among many aquatic taxa. When a novel, neutral stimulus is presented in tandem with chemical cues from an injured conspecific, an association is formed between the novel stimulus and apparent risk. Learned recognition of predation risk is well documented for fathead minnows, Pimephales promelas. When minnows detect alarm cues in nature they are also potentially exposed to multiple environmental stimuli, few of which are likely to be relevant indicators of risk. How do minnows discern among candidate stimuli potentially associated with predation risk? Two possibilities are shape and motion. In this study, individual piscivore‐naïve minnows were presented simultaneously with conspecific chemical alarm cues and two stimulus objects. One object was a darkened tube with its long axis in the horizontal plane (fish‐like). The second object was a black disk. Following introduction of chemical alarm cues, one of the objects was raised and lowered repeatedly. After a single conditioning trial, minnows associated risk significantly more with the previously moving object than the previously stationary object, as indicated by reduced activity. Object shape had no significant effect on response intensity in test trials. Our data suggest that minnows have been selected to form aversive responses to moving objects at a site of recent predation because movement is a more predictable indicator of predator identity than shape.     

Exposure to a contextually neutral stressor potentiates fear conditioning in juvenile rainbow trout,Oncorhynchus mykiss

Organisms faced with stressors deploy a suite of adaptive responses in the form of behavioral, physiological and cognitive modifications to overcome the challenge. Interactive effects of these responses are known to influence learning and memory processes and facilitation is thought to be dependent, in part, upon contextual relevance of the stressor to the learning task. Predation is one such stressor for prey animals, and their ability to manage reliable information about predators is essential for adaptive antipredator strategies. Here, we investigated (i) the influence cortisol has on the ability of juvenile rainbow trout to learn and retain conditioned antipredator responses to predatory cues, and (ii) whether conditioned behavioral and physiological responses to predator cues are fixed or deployed in a threat-sensitive manner. Trout were fed cortisol-coated pellets minutes prior to a conditioning event where they were exposed to novel predator odor paired with chemical alarm cues (unconditioned stimulus). We tested for conditioned responses by exposing trout to predator cues after 2, 4 or 10 days and subsequently documented physiological and behavioral responses. Both control and cortisol-fed trout learned the predator odor and responded 2 and 4 days post conditioning. However, at 10 days only cortisol-fed trout maintained strong behavioral responses to predator cues. Interestingly, we failed to find conditioned physiological responses to predator odor despite the presence of threat-sensitive cortisol responses to the unconditioned stimulus. Our findings suggest cortisol exposure prior to predator-learning may enhance retention of conditioned responses, even without a contextual link between stressor source and learning task.     

Effects of exposure to predatory cues on territorial behaviour of male fathead minnows

We conducted a laboratory study to determine if male fathead minnows, Pimephales promelas, altered their territorial behaviour associated with reproduction in response to combinations of visual and chemical cues from northern pike, Esox lucius. We introduced the following stimuli to a territorial male: a brick (control), fathead minnow alarm pheromone, a pike fed brook stickleback, Culea inconstans, or a pike fed fathead minnow. The territorial behaviour of males did not change when the control was added. Male minnows experiencing threat from pike fed stickleback significantly reduced the frequency at which they performed three territorial behaviours, but, within 12 h, had returned to pre-exposure activity levels. Male minnows subjected to alarm pheromone alone and to pike fed fathead minnow significantly reduced their territorial behaviour, abandoned their nests, and did not return to pre-exposure levels of activity after 24 h. We suggest that because risk of predation triggers prolonged decreases in territorial defense, it may affect competition between nesting males and female mate choice. We conclude that fathead minnows can assess the severity of predatory threat and adjust their reproductive behaviour accordingly.