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.     

Differential learning rates of chemical versus visual cues of a northern pike by fathead minnows in a natural habitat

We stocked 39 juvenile pike, Esox lucius, into a previously pike free pond which contained a population of approximately 78 000 fathead minnows, Pimephales promelas. Fathead minnows sampled prior to pike stocking did not show a stereotypic fright response to either visual or chemical cues from pike. After stocking pike, we sampled minnows every two days for a period of two weeks. Minnows sampled six days after stocking still did not show a fright response to the sight of a pike, but those sampled eight days after stocking did exhibit a significant fright response, indicating that acquired predator recognition based on vision occurred between six and eight days. Minnows sampled two days after stocking did not show a fright response to chemical cues of a pike. Those sampled four days after did, however, exhibit a significant fright response, indicating that acquired predator recognition based on chemical cues occurred between two and four days. These data indicate that acquired predator recognition occurs very rapidly and that the rate of learning of predator identity differs for chemical versus visual cues.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

Effects of northern pike on patterns of nest use and resproductive behavior of male fathead minnows in a boreal lake

We conducted a two-part study to assets predator avoidance byreproductive male fathead minnows (Pimephales promelos) subjectedto predation threat from northern pike (Esox lucius). First,we determined if patterns of nest use by egg-guarding male minnowsin a boreal lake were related to pike densities. We samplednorthern pike and identified four areas of "high pike-density"and three areas of "low pike-density." We censused natural nestsand placed nest boards in these areas. We found eggs on naturalnests more frequently in areas with low densities of pike thanin areas with high densities of pike. However, we could notfully explain the distribution of nests by predation risk. Second,we evaluated the behavioral response of egg-guarding males toa control stimulus (a piece of wood) or a live pike in a wirecage. We used time to return to the nest after a stimulus asa measure of risk taking. Males took different amounts of riskbased on predation threat; males in the predator treatment tooklonger to return to their nests than control males. Risk takingwas not related to the number or age of the eggs but to distanceto nearest egg-guarding neighbor; males with close neighborsreturned sooner than more isolated males. Males in the predatortreatment had lower total activity and egg rubbing than controlmales after they returned to their nests. We conclude that malefathead minnows altered their reproductive behavior in waysthat reduced predation risk, but the cost of predator avoidancemight include egg predation, lost mating opportunities, or usurpationof nests     

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.     

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.     

Predator attack motivation influences the inspection behaviour of European minnows

Predator inspection behaviour at different levels of attack motivation (attack status of the predator) was investigated in European minnows Phoxinus phoxinus from a population sympatric with pike Esox lucius , during controlled laboratory experiments. Shoals of minnows performed more predator inspections and formed larger inspection group sizes shortly after an attack by a pike. After inspection, minnows returned to the safety of the main shoal, regardless of predator motivation. Minnows which inspected last-before and first-after a strike by a pike modified their behaviour after inspection; they reduced feeding, increased shoaling, flicked their dorsal and pectoral fins and skittered. This behaviour signified alarm and appeared to reflect the severity of the threat posed by the predator at the time of inspection. Fish that had inspected when the pike displayed low attack motivation did not modify their behaviour after inspection to reflect alarm. Information concerning the attack motivation of the predator is probably transferred passively throughout the shoal by changed inspector behaviour and by inspection rate. These data demonstrate that: (1) minnows modified their behaviour after inspection to reflect a predator's attack motivation; and (2) minnows which inspected immediately before a strike appeared to anticipate the future attack and modified their behaviour accordingly.     

Behavior of fish predators and their prey: habitat choice between open water and dense vegetation

Synopsis Behavior of largemouth bass, Micropterus salmoides, and northern pike, Esox lucius, foraging on fathead minnows, Pimephales promelas, or bluegills, Lepomis macrochirus, was quantified in pools with 50% cover (half the pool had artificial stems at a density of 1000 stems m⁻²). Both predators spent most of their time in the vegetation. Largemouth bass searched for bluegills and ambushed minnows, whereas the relatively immobile northern pike ambushed all prey. Minnows were closer to predators and were captured more frequently than bluegills. Even when minnows dispersed, they moved continually and eventually wandered within striking distance of a predator. Bluegills dispersed in the cover with predators. Bass captured the few bluegills that strayed into the open and pike captured those that approached too closely in the cover. The ability of predators to capture prey while residing in habitats containing patches of dense cover may explain their residence in areas often considered to be poor ones for foraging. The unit is sponsored jointly by the United States Fish and Wildlife Service, Ohio Department of NaturalResources, The Ohio State University, and the Wildlife Management Institute     

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.     

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.     

Information Transfer across Fish Shoals under Predator Threat

The hypothesis that shoaling fish can obtain information about a predator's approach from changes in the behaviour of other shoal members was tested in an experiment in which receiver minnows (Phoxinus phoxinus) behind a one-way-mirror could observe the reaction of transmitter minnows threatened by the stalk of a pike (Esox lucius) model. Although the receiver minnows were out of visual contact with the pike model they decreased their foraging behaviour and started hiding when the pike model came towards the feeding patch of the transmitter fish. The presence of skittering behaviour and inspection behaviour in the transmitter but not in the receiver fish suggests that individual confirmation of the predator does play a role in determining the nature of the anti-predator response. Nevertheless there is clear evidence that receiver fish modify their own behaviour on the basis of information obtained from individuals which have seen a predator.     

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.