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.     

Smell, learn and live: The role of chemical alarm cues in predator learning during early life history in a marine fish

The speed with which individuals can learn to identify and react appropriately to predation threats when transitioning to new life history stages and habitats will influence their survival. This study investigated the role of chemical alarm cues in both anti-predator responses and predator identification during a transitional period in a newly settled coral reef damselfish, Pomacentrus amboinensis. Individuals were tested for changes in seven behavioural traits in response to conspecific and heterospecific skin extracts. Additionally, we tested whether fish could learn to associate a previously novel chemical cue (i.e. simulated predator scent) with danger, after previously being exposed to a paired cue combining the conspecific skin extract with the novel scent. Fish exposed to conspecific skin extracts were found to significantly decreased their feeding rate whilst those exposed to heterospecific and control cues showed no change. Individuals were also able to associate a previously novel scent with danger after only a single previous exposure to the paired conspecific skin extract/novel scent cue. Our results indicate that chemical alarm cues play a large role in both threat detection and learned predator recognition during the early post-settlement period in coral reef fishes.     

Who dares, learns: chemical inspection behaviour and acquired predator recognition in a characin fish

Individuals that dare approach predators (predator inspection behaviour) may benefit by acquiring information regarding the potential threat of predation. Although information acquisition based on visual cues has been demonstrated for fish, it is unknown whether fish will inspect predators on the basis of chemical cues or whether such inspection behaviour results in information acquisition. Here, we first ascertained whether predator inspection behaviour can be mediated by chemical cues from predators by exposing groups of predator-naive glowlight tetras (Hemigrammus erythrozonus) to the chemical cues of a potential fish predator (convict cichlid Cichlasoma nigrofasciatum) that had been fed either tetras (which possess an alarm pheromone) or swordtails (Xiphophorus helleri, which lack Ostariophysan alarm pheromones). Tetras showed a significant increase in antipredator behaviour when exposed to the tetra-diet cue, but not when exposed to the swordtail-diet cue. Chemically mediated predator inspection behaviour was also affected. Both the latency to inspect and the minimum approach distance to the predator significantly increased, and the mean number of inspectors per predator inspection visit significantly decreased when tetras were exposed to the tetra-diet versus the swordtail-diet chemical cues. We then examined a potential benefit associated with chemically mediated predator inspection behaviour. Only tetras that were initially exposed to the tetra-diet cue and that had inspected the predator acquired the visual recognition of a convict cichlid as a predation threat. Our results thus demonstrate that (1) predator inspection behaviour in the glowlight tetra can be initiated by chemical cues, (2) chemically mediated inspection behaviour is affected by the presence of alarm pheromone, and (3) inspectors benefit by acquiring the recognition of novel predators. Copyright 1999 The Association for the Study of Animal Behaviour.     

Responses of tadpoles to hybrid predator odours: strong maternal signatures and the potential risk/response mismatch

Previous studies have established that when a prey animal knows the identity of a particular predator, it can use this knowledge to make an ‘educated guess'' about similar novel predators. Such generalization of predator recognition may be particularly beneficial when prey are exposed to introduced and invasive species of predators or hybrids. Here, we examined generalization of predator recognition for woodfrog tadpoles exposed to novel trout predators. Tadpoles conditioned to recognize tiger trout, a hybrid derived from brown trout and brook trout, showed generalization of recognition of several unknown trout odours. Interestingly, the tadpoles showed stronger responses to odours of brown trout than brook trout. In a second experiment, we found that tadpoles trained to recognize brown trout showed stronger responses to tiger trout than those tadpoles trained to recognize brook trout. Given that tiger trout always have a brown trout mother and a brook trout father, these results suggest a strong maternal signature in trout odours. Tadpoles that were trained to recognize both brown trout and brook trout showed stronger response to novel tiger trout than those trained to recognize only brown trout or only brook trout. This is consistent with a peak shift in recognition, whereby cues that are intermediate between two known cues evoke stronger responses than either known cue. Given that our woodfrog tadpoles have no evolutionary or individual experience with trout, they have no way of knowing whether or not brook trout, brown trout or tiger trout are more dangerous. The differential intensity of responses that we observed to hybrid trout cues and each of the parental species indicates that there is a likely mismatch between risk and anti-predator response intensity. Future work needs to address the critical role of prey naivety on responses to invasive and introduced hybrid predators.     

The smell of danger: chemical recognition of fish predators by the invasive crayfish Procambarus clarkii

1. Since avoiding predation can compromise animal fitness, prey are expected to respond to different predator species with an intensity appropriate to the level of risk. In fresh waters, the threat of predation is typically assessed by chemical cues, in particular by odours released by either injured/disturbed conspecifics (conspecific alarm odour) or predators (predator odours). Here, we used the most widely distributed crayfish in the world, the invasive North American Procambarus clarkii, to investigate the relative effectiveness of odours emitted by fish predators compared with conspecific alarm odour. We also tested whether P. clarkii is able to discriminate between fish predators of which it has ‘experience’ (either recent, via introduction to the same water body, or old, by sharing a native range), as well as between fish predators that pose low or high risk. 2. The study was carried out on introduced populations of P. clarkii from two sites, characterised by different fish assemblages: the Malewa River (a tributary of Lake Naivasha, Kenya) and Lake Trasimeno (Italy). Laboratory experiments consisted of three sequential phases (‘water’, ‘food’ and ‘smell’ phases) and five treatments. Treatments differed in the odour presented during the smell phase, i.e. no odour (plain water) and odours from either injured conspecifics or three fish species per site. Crayfish from the Malewa River population were confronted with the odours of largemouth bass (Micropterus salmoides), common carp (Cyprinus carpio) and tilapia (Tilapia zillii) (all introduced to Lake Naivasha but absent from the Malewa River), and those from the Lake Trasimeno population with the odours of the introduced largemouth bass and carp and the native chub (Squalius cephalus). Largemouth bass is the only predator that imposes a high risk to crayfish, and it also shares its native range with P. clarkii. We analysed the time spent by crayfish feeding, in locomotion and in adopting a raised or lowered posture. A reduction in the time spent feeding and in locomotion, and an increase in the time spent in the lowered posture were considered to indicate alarm. 3. Crayfish from both populations responded with a more pronounced reduction in feeding to conspecific alarm odour rather than to predator odours. Crayfish from the Malewa River reacted with the same intensity to the odours of the three fish species tested, whereas, in Lake Trasimeno, the odour of largemouth bass was significantly more threatening than the odours of the other two species. 4. Procambarus clarkii seems to perceive a general fish odour that alerts it to possible predation risk without the need of either a direct recent experience or via sharing a common native range. However, where they coexist with fish, crayfish become able to distinguish among species, adapting the intensity of their response to the effective risk. Our results confirm the relatively high learning capacity of P. clarkii reported in previous studies and suggest the existence of mechanisms that make predator recognition particularly efficient in this extraordinarily successful invader.     

Alarm cue induces an antipredator morphological defense in juvenile Nicaragua cichlids Hypsophrys nicaraguensis

Olfactory cues that indicate predation risk elicit a number of defensive behaviors in fishes, but whether they are sufficient to also induce morphological defenses has receivedlittle attention. Cichlids are characterized by a high level of morphological plasticity during development, and the few species that have been tested do exhibit defensive behaviors when exposed to alarm cues released from the damaged skin of conspecifics. We utilized young juvenile Nicaragua cichlids Hypsophrys nicaraguensis to test if the perception of predation risk from alarm cue (conspecific skin extract) alone induces an increased relative body depth which is a defense against gape-limited predators. After two weeks of exposure, siblings that were exposed to conspecific alarm cue increased their relative body depth nearly double the amount of those exposed to distilled water (control) and zebrafish Danio rerio alarm cue. We repeated our measurements over the last two weeks (12 and 14) of cue exposure when the fish were late-stage juveniles to test if the rate of increase was sustained; there were no differences in final dimensions between the three treatments. Our results show that 1) the Nicaragua cichlid has an innate response to conspecific alarm cue which is not a generalized response to an injured fish, and 2) this innate recognition ultimately results in developing a deeper body at a stage of the life history where predation risk is high [Current Zoology 56 (1): 36-42, 2010].     

Antipredator Behavior of American Bullfrogs (Lithobates catesbeianus) in a Novel Environment

Invasive species capable of recognizing potential predators may have increased establishment rates in novel environments. Individuals may retain historical predator recognition and invoke innate responses in the presence of taxonomically or ecologically similar predators, generalize antipredator responses, or learn to avoid risky species in novel environments. Invasive amphibians in aquatic environments often use chemical cues to assess predation risk and learn to avoid novel predators via direct experience and/or associated chemical cues. Ontogeny may also influence recognition; experience with predators may need to occur at certain developmental stages for individuals to respond correctly. We tested predator recognition in invasive American bullfrog ( Lithobates catesbeianus) tadpoles that varied in experience with fish predators at the population and individual scale. We found that bullfrog tadpoles responded to a historical predator, largemouth bass ( Micropterus salmoides), only if the population was locally sympatric with largemouth bass. Individuals from a population that did not co‐occur with largemouth bass did not increase refuge use in response to either largemouth bass chemical cues alone or chemical cues with diet cues (largemouth bass fed bullfrog tadpoles). To test whether this behavioral response was generalized across fish predators, we exposed tadpoles to rainbow trout ( Oncorhynchus mykiss) and found that tadpoles could not recognize this novel predator regardless of co‐occurrence with other fish species. These results suggest that environment may be more important for predator recognition than evolutionary history for this invasive species, and individuals do not retain predator recognition or generalize across fish predators.     

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.     

Olfactory assessment of predation risk in the aquatic environment

The aquatic environment is well suited for the transmission of chemical information. Aquatic animals have evolved highly sensitive receptors for detecting these cues. Here, I review behavioural evidence for the use of chemical cues by aquatic animals for the assessment of predation risk. Chemical cues are released during detection, attack, capture and ingestion of prey. The nature of the cue released depends on the stage of the predation sequence in which cues are released. Predator odours, disturbance pheromones, injury-released chemical cues and dietary cues all convey chemical information to prey Prey use these cues to minimize their probability of being taken on to the next stage of the sequence. The evolution of specialized epidermal alarm substance cells in fishes in the superorder Ostariophysi represent an amplification of this general phenomenon. These cells carry a significant metabolic cost. The cost is offset by the fitness benefit of the chemical attraction of predators. Attempts of piracy by secondary predators interrupt predation events allowing prey an opportunity for escape. In conclusion, chemical cues are widely used by aquatic prey for risk assessment and this has resulted in the evolution of specialized structures among some taxa.     

Habitat degradation disrupts neophobia in juvenile coral reef fish

Habitat degradation not only disrupts habitat‐forming species, but alters the sensory landscape within which most species must balance behavioural activities against predation risk. Rapidly developing a cautious behavioural phenotype, a condition known as neophobia, is advantageous when entering a novel risky habitat. Many aquatic organisms rely on damage‐released conspecific cues (i.e. alarm cues) as an indicator of impending danger and use them to assess general risk and develop neophobia. This study tested whether settlement‐stage damselfish associated with degraded coral reef habitats were able to use alarm cues as an indicator of risk and, in turn, develop a neophobic response at the end of their larval phase. Our results indicate that fish in live coral habitats that were exposed to alarm cues developed neophobia, and, in situ, were found to be more cautious, more closely associated with their coral shelters and survived four‐times better than non‐neophobic control fish. In contrast, fish that settled onto degraded coral habitats did not exhibit neophobia and consequently suffered much greater mortality on the reef, regardless of their history of exposure to alarm cues. Our results show that habitat degradation alters the efficacy of alarm cues with phenotypic and survival consequences for newly settled recruits.     

Responses of larval dragonflies to conspecific and heterospecific predator cues

Abstract.  1. In cannibalistic populations, smaller individuals are subject to predation by larger conspecifics, and small individuals commonly alter their behaviour in response to cannibals. Little is known, however, about the underlying cues that trigger such responses and how the behavioural responses to conspecific cannibals differ from heterospecific predators.
2. This study tests which cues are used for the detection of conspecific predators in the larva of the dragonfly Plathemis lydia and how the behavioural response to cannibals differed from the response to heterospecific predators.
3. Individuals were exposed to chemical cues, visual cues, and a combination of both cues from conspecifics as well as no predator and heterospecific predator controls during which their activity and feeding rates were observed.
4. Individuals increased their activity, spatial movement and feeding behaviour in response to either visual or chemical cues from conspecific predators, which was opposite to responses displayed with cues from heterospecific predators. Interestingly, the responses to visual and chemical cues from conspecifics combined were weaker than to either cue in isolation and similar to the no cue control.
5. The results clearly indicate that individuals are able to use chemical and visual cues to detect even very subtle differences in phenotype of conspecific predators.
6. The opposite response in behaviour when exposed to conspecific cannibals vs. heterospecific predators suggests that the presence of cannibals will increase the mortality risk of small individuals due to heterospecific predation. This risk-enhancement is likely to have important consequences for the dynamics of predator–prey interactions.     

Behavioural response of bullfrog tadpoles to chemical cues of predation risk are affected by cue age and water source

When confronted by signals of predators presence, many aquatic organisms modify their phenotype (e.g., behaviour or morphology) to reduce their risk of predation. A principal means by which organisms assess predation risk is through chemical cues produced by the predators and/or prey during predation events. Such responses to predation risk can directly affect prey fitness and indirectly affect the fitness of species with which the prey interacts. Accurate assessment of the cue will affect the adaptive nature, and hence evolution, of the phenotypic response. It is therefore, important to understand factors affecting the assessment of chemical cues. Here I examined the effect of the age of chemical cues arising from an invertebrate predator, a larval dragonfly (Anax junius), which was fed bullfrog tadpoles, on the behavioural response (activity level and position) of bullfrog tadpoles. The bullfrog response to chemical cues declined as a function of chemical cue age, indicating the degradation of the chemical cue was on the order of 2–4 days. Further, the decay occurred more rapidly when the chemical cue was placed in pond water rather than well water. These results indicate a limitation of the tadpoles to interpret factors that affect the magnitude of the chemical cue and hence accurately assess predation risk. These findings also have implications for experimental design and the adaptation of phenotypic responses to chemical cues of predation risk.     

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.     

Damage released prey alarm substances or predator odours? Risk assessment by an aquatic oligochaete

Although the abilities of prey to detect and respond to chemical substances associated with a predator have been widely reported, the factors promoting the evolution of responses to prey alarm cues vs. predator odours are still vague. In this article, we combined field research with laboratory experiments to explore which chemical substance associated with predator activity (predator odour, conspecific or heterospecific alarm substances) induces defence responses in the aquatic oligochaete Stylaria lacustris, which is vulnerable to common littoral predators. The field results indicated that predators injure the oligochaetes and a great proportion, up to 45% of individuals in the population, were found to be damaged. The results of the laboratory experiments revealed that chemical odours from damselfly larvae feeding on S. lacustris did not induce the defence response in the oligochaetes. On the contrary, oligochaetes detected and responded to alarm substances from damaged conspecifics alone and substances from damaged cladoceran Daphnia magna. We discussed conditions favouring the responses to damage released prey alarm cues instead of predator odours in Stylaria lacustris. Our data suggest that the selection of responses to alarm cues from damaged prey vs. predator odours may be dependent on three factors: (1) non-species-specific predation, (2) divergence of food niche of the different stages of the predator and (3) complex food web with multiple predators. Handling editor: S. Declerk     

The Sound of Danger: Threat Sensitivity to Predator Vocalizations,Alarm Calls,and Novelty in Gulls

The threat sensitivity hypothesis predicts that organisms will evaluate the relative danger of and respond differentially to varying degrees of predation threat. Doing so allows potential prey to balance the costs and benefits of anti-predator behaviors. Threat sensitivity has undergone limited testing in the auditory modality, and the relative threat level of auditory cues from different sources is difficult to infer across populations when variables such as background risk and experience are not properly controlled. We experimentally exposed a single population of two sympatric gull species to auditory stimuli representing a range of potential threats in order to compare the relative threat of heterospecific alarm calls, conspecific alarms calls, predator vocalizations, and novel auditory cues. Gulls were able to discriminate among a diverse set of threat indicators and respond in a graded manner commensurate with the level of threat. Vocalizations of two potential predators, the human voice and bald eagle call, differed in their threat level compared to each other and to alarm calls. Conspecific alarm calls were more threatening than heterospecfic alarm calls to the larger great black-backed gull, but the smaller herring gull weighed both equally. A novel cue elicited a response intermediate between known threats and a known non-threat in herring gulls, but not great black-backed gulls. Our results show that the relative threat level of auditory cues from different sources is highly species-dependent, and that caution should be exercised when comparing graded and threshold threat sensitive responses.     

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.     

Embryonic and larval defensive responses of agile frog (Rana dalmatina) to alien crayfish

Red swamp crayfish Procambarus clarkii, a widespread invasive alien crayfish, represents a serious threat for several freshwater species, including amphibians, which are declining at a global scale. As a shared coevolutionary history is the main factor determining the emergence of antipredator responses, Anuran tadpoles may not be able to cope effectively with this introduced predator. We performed two experiments to assess agile frog's (Rana dalmatina) defensive responses to both P. clarkii and native dragonfly larvae (Anax imperator). First, we conditioned embryos (collected from two ponds 30 km away from each other) with predators’ chemical cues to explore possible variation in hatching time caused by predation risk. In the second experiment, to evaluate how predators’ diet affects tadpole behavior, we conditioned tadpoles for a 5‐week period with cues from tadpole‐fed and gammarid‐fed predators and recorded behavioral and morphological responses. Embryos did not alter hatching time in the presence of any predator cue, while tadpoles from both populations strongly reduced activity and visibility when raised in the presence of tadpole‐fed dragonfly larvae. Morphological changes were less straightforward and were induced only in one population, for which broader tails and a slight increase in body size of tadpoles exposed to tadpole‐fed predators were observed. The lack of defensive responses in crayfish‐exposed tadpoles suggests that the spreading of this invasive species in agricultural lowlands of northern Italy may represent a further threat to their conservation.     

Antipredator responses to skin extract of redbelly dace, <Emphasis Type="Italic">Phoxinus eos, </Emphasis>by free-ranging populations of redbelly dace and fathead minnows,<Emphasis Type="Italic">Pimephales promelas</Emphasis>

Synopsis Fishes in the superorder Ostariophysi possess specialized epidermal cells that contain a chemical alarm cue. The alarm cue is released when the skin is damaged during a predatory attack. Therefore, the cue serves as a reliable indicator of predation risk to nearby conspecifics and ecologically similar heterospecifics with which it shares predators. Antipredator behavior in response to these alarm cues has been demonstrated in numerous studies in confined spaces (laboratory aquaria, field traps, fluvarium). When tested on a natural field population however, behavioral response has been inconsistent. Here, we expose free-ranging redbelly dace and fathead minnows to skin extract of redbelly dace and record their behavioral response with an underwater video camera. We observed avoidance of areas in which skin extract was introduced, but no avoidance of areas in which water (control) was introduced. These data confirm the ecological function of skin extract in mediating predator–prey interactions in aquatic habitats, and argue against the hypothesis that alarm reactions are an artifact of confined spaces.     

Experimental evidence for innate predator recognition in the Seychelles warbler.

Nest predation is a major determinant of fitness in birds and costly nest defence behaviours have evolved in order to reduce nest predation. Some avian studies have suggested that predator recognition is innate whereas others have stressed the importance of learning. However, none of these studies controlled for the genetic origin of the populations investigated and the effect of unfamiliarity with the predator. Here we determined whether experience with a nest predator is a prerequisite for nest defence by comparing predator recognition responses between two isolated but genetically similar Seychelles warbler (Acrocephalus sechellensis) populations, only one of which had experience of the egg predating Seychelles fody (Foudia sechellarum). Individuals in the predator-free population significantly reduced nest guarding compared to individuals in the population with the predator, which indicates that this behaviour was adjusted to the presence of nest predators. However, recognition responses (measured as both alarm call and attack rates) towards a mounted model of the fody were equally strong in both populations and significantly higher than the responses towards either a mounted familiar non-predator and a mounted, novel, non-predator bird species. Responses did not differ with a warbler's age and experience with the egg predator, indicating that predator recognition is innate.     

Asymmetrical generalisation between pheromonal and floral odours in appetitive olfactory conditioning of the honey bee (Apis mellifera L.)

The capacity to generalise between similar but not identical olfactory stimuli is crucial for honey bees, allowing them to find rewarding food sources with varying volatile emissions. We studied bees' generalisation behaviour with odours having different biological values: typical floral odours or alarm compounds. Bees' behavioural and peripheral electrophysiological responses were investigated using a combined proboscis extension response conditioning-electroantennogram assay. Bees were conditioned to pure linalool (floral) or to pure isoamyl acetate (alarm) and were tested with different concentrations of both compounds. Electrophysiological responses were not influenced by conditioning, suggesting that the learning of individual compounds does not rely on modulations of peripheral sensitivity. Behaviourally, generalisation responses of bees conditioned to the alarm compound were much higher than those of bees conditioned to the floral odour. We further demonstrated such asymmetrical generalisation between alarm and floral odours by using differential conditioning procedures. Conditioning to alarm compounds (isoamyl acetate or 2-heptanone) consistently induced more generalisation than conditioning to floral compounds (linalool or phenylacetaldehyde). Interestingly, generalisation between the two alarm compounds, which are otherwise chemically different, was extremely high. These results are discussed in relation to the neural representation of compounds with different biological significance for bees.