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.     

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.     

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.     

Learned Recognition of Heterospecific Alarm Signals: The Importance of a Mixed Predator Diet

A wide diversity of aquatic organisms release alarm signals upon being attacked by a predator. Alarm signals may 'warn' nearby individuals of danger. Moreover, the signals may be important in facilitating learned recognition of unknown stimuli. It is common for different prey species to respond to each other's chemical alarm signals. In many cases, the responses are learned but no learning mechanisms have been identified to date. In this study we tested whether prey fish can learn the identity of an unknown alarm signal when they detect it in association with conspecific alarm cues in the diet of a predator. Chemical alarm cues are known to be conserved in the diet of predators. We conditioned fathead minnows ( Pimephales promelas ) with chemical stimuli from predatory yellow perch ( Perca flavescens ) fed a mixed diet of minnows and brook stickleback ( Culaea inconstans ), perch fed a mixed diet of swordtails ( Xiphophorus helleri ) and stickleback or distilled water. Minnows were subsequently exposed to chemical alarm cues of injured stickleback alone. Those minnows previously conditioned with perch fed a mixed diet of minnows and stickleback increased their use of shelter and 'froze' significantly more than minnows previously conditioned with perch fed a diet of swordtails and stickleback or those exposed to distilled water. These data demonstrate a mechanism by which minnows can learn the identity of a heterospecific alarm signal.     

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.     

Free—living fathead minnows rapidly learn to recognize pike as predators

Individuals from a natural population of approximately 20 000 fathead minnows from a pike–free pond did not respond with appropriate anti–predator behaviour upon encountering pike odour in laboratory tests. However, 14 days after 10 pike were stocked into the pond, minnows had acquired recognition of pike odour. Laboratory studies have indicated several possible mechanisms for acquiring predator recognition in fathead minnows. This study indicates that these, or similar processes, can produce major changes in predator recognition in the wild.     

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.     

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.     

Acquired Recognition of Predator Odour in the European Minnow (Phoxinus phoxinus)

Naive European minnows (Phoxinus phoxinus) do not show a fright reaction when they first encounter the odour of a natural predator (the pike: Esox lucius) or the odour of a non-piscivorous exotic (tilapia: Tilapia mariae). A conditioned fright response to both these odours will however develop if minnows experience them in a potentially dangerous situation, for example, in conjunction with Schreckstoff, the ostariophysian alarm pheromone. Although minnows respond to both odours the reaction to the tilapia odour is reduced. This suggests that a constraint on learning is involved. Olfactory recognition is particularly valuable for detecting predators that hunt in conditions where visibility is poor.     

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.     

Chemical alarm signals increase the survival time of fathead minnows (Pimephales promelas) during encounters with northern pike (Esox Lucius)

We tested the hypothesis that exposure to a conspecific alarmpheromone improves survival of fathead minnows (Pimephales promelas)during staged encounters with an unfamiliar predator (northernpike: Esox luaus). Minnows exposed to the alarm pheromone survived39. 5% longer than controls. This difference in survival timeappeared to result not from direct inhibition of the pike butrather from some aspect of the minnows' antipredator behavior.Minnows exhibited significant increases in both shoaling andshelter use after exposure to the alarm pheromone. For controlminnows, the degree of shoaling was positively correlated withsurvival time, suggesting that increased shoaling is an effectiveantipredator response. This study provides the first directexperimental evidence that chemical alarm signals in fishesimprove survival of receivers.     

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.     

Population Differences in Responses of Fathead Minnows (Pimephales promelas) to Visual and Chemical Stimuli from Predators

Fathead minnows (Cyprinidae: Pimephales promelas) from a population that is sympatric with predatory northern pike (Esocidae: Esox lucius) exhibited a fright reaction to the visual stimulus of a live northern pike significantly more often than minnows from a population that is allopatric with pike. The fright response included increased use of shelter, dashing and freezing. Minnows from the pike-sympatric population also exhibited a significantly greater fright response, measured as a reduction in activity, following exposure to chemical stimuli from pike (i.e. water from a tank that had contained a pike) than did minnows from the pike-allopatric population. There was no significant change in activity by minnows from either population following exposure to chemical stimuli from nonpiscivorous peacock gudgeons (Eleotridae: Tateurndina ocellicauda), suggesting that the difference between the two populations is specific to stimuli from pike rather than a general difference in response to chemical stimuli from heterospecific fishes. Fathead minnows apparently utilize at least a two-tiered predator recognition system that incorporates both visual and chemical cues.     

Generalization of learned predator recognition: an experimental test and framework for future studies

While some prey species possess an innate recognition of their predators, others require learning to recognize their predators. The specific characteristics of the predators that prey learn and whether prey can generalize this learning to similar predatory threats have been virtually ignored. Here, we investigated whether fathead minnows that learned to chemically recognize a specific predator species as a threat has the ability to generalize their recognition to closely related predators. We found that minnows trained to recognize the odour of a lake trout as a threat (the reference predator) generalized their responses to brook trout (same genus as lake trout) and rainbow trout (same family), but did not generalize to a distantly related predatory pike or non-predatory suckers. We also found that the intensity of antipredator responses to the other species was correlated with the phylogenetic distance to the reference predator; minnows responded with a higher intensity response to brook trout than rainbow trout. This is the first study showing that prey have the ability to exhibit generalization of predator odour recognition. We discuss these results and provide a theoretical framework for future studies of generalization of predator recognition.     

Learned Recognition of Novel Predator Odour by Zebra Danios, Danio Rerio, Following Time-shifted Presentation of Alarm Cue And Predator Odour

Fishes in the superorder ostariophysi possess specialized epidermal cells that contain an alarm cue. Fish associate novel odours, such as the odour of a predator, with predation risk after a single, simultaneous exposure to the novel odour and alarm cue. Thereafter, the novel cue is recognized as an indicator of risk and its presence induces antipredator behaviour. Two common antipredator behaviours are reduction in activity and movement to the bottom. This phenomenon has been demonstrated many times in the laboratory setting for a variety of aquatic taxa. In nature however, the detection of novel predator odour may be time-shifted with respect to the detection of alarm cues. Is there a critical period immediately upon the detection of alarm cue in which associative learning can occur? We presented zebra danios, Danio rerio, with the odour of northern pike, Esox lucius, 5?min after presenting them with either alarm cue or water (control). During a predation event, 5?min is a long time. When later retested with pike odour alone, zebra fish conditioned with alarm cue significantly increased antipredator behaviour in terms of decreased activity and movement towards the bottom. Control fish did not recognize pike odour as dangerous when retested. These data show that learned recognition of predation risk is sufficiently robust to accommodate ecologically realistic temporal shifts in stimulus presentation.     

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.     

Population differences in the reaction of minnows to alarm substance*

Experiments showed that minnows, Phoxinus phoxinus, sympatric with pike, Esox lucius, responded more vigorously to alarm substance than minnows from a population with no experience of pike predation in the wild. Minnows from the pike-sympatric (Dorset) population were more likely to hide and less likely to risk feeding than their pike-allopatric (Gwynedd) counterparts. The reaction to alarm substance in the pike-sympatric population was further increased when it was presented along with the visual stimulus of a ‘stalking’ model pike. When the Dorset minnows experienced both alarm substance and the pike model together they reduced their inspection behaviour to a level below that of the Gwynedd minnows. Minnows from the Gwynedd (pike-allopatric) population displayed increased levels of shoaling in the treatments in which alarm substance was used.     

Effect of cycles of feed deprivation on growth and food consumption of immature three-spined sticklebacks and European minnows

Individual juvenile three-spined sticklebacks Gasterosteus aculeatus and European minnow Phoxinus phoxinus , from sympatric populations, were subjected to four cycles of 1 week of food deprivation and 2 weeks of ad libitum feeding. Mean specific growth rate during the weeks of deprivation was negative and did not differ between species. The three-spined stickleback showed sufficient growth compensation to recover to the growth trajectory shown by control fish daily fed ad libitum . The compensation was generated by hyperphagia during the re-feeding periods, and in the last two periods of re-feeding, the gross growth efficiencies of deprived three-spined sticklebacks were greater than in control fish. The expression of the compensatory changes in growth and food consumption became clearer over the successive periods of re-feeding. The European minnow developed only a weak compensatory growth response and the mass trajectory of the deprived fish deviated more and more from the control trajectory. During re-feeding periods, there were no significant differences in food consumption or gross growth efficiency between control and deprived European minnows. The differences between the two species are discussed in terms of the possible costs of compensatory growth, the control of growth and differences in feeding biology.     

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.     

Social Context Influences the Antipredator Behaviour of Fathead Minnows to Chemical Alarm Cues

Prey fishes, like many organisms under fluctuating predation threat, rely on multiple sources of information to accurately gauge current risk. This includes the use of chemical cues such as alarm cues from damaged conspecifics or familiar heterospecifics, as well as the odour of known predators. While each fish is well equipped with its own array of sensory abilities, they should also be alert to the behaviours of nearby neighbours who may have information they lack. In the present study, we tested the ability of fathead minnows to use social cues in combination with the odour of damaged conspecifics and heterospecifics to mediate the assessment of predation risk. Specifically, we tested whether the presence of a shoal of conspecifics or familiar heterospecifics would significantly change a minnow's antipredator behaviour when exposed to the odour of a damage‐release cue from a conspecific or ecologically similar heterospecific. The results of our study showed a significant interaction between the damage‐release cues to which the minnows were exposed and the presence/absence of shoalmates. These findings have important implications for the design of future investigations of antipredator responses because most studies of group‐living prey have been conducted on solitary subjects.