Familiarity and shoal cohesion in fathead minnows (Pimephales promelas): implications for antipredator behaviour

We exposed groups of four fathead minnows (Pimephales promelas) that were familiar to each other and had been taken from naturally occurring shoals, and groups of four fish unfamiliar to each other, taken from four separate shoals, to either chemical stimuli from pike or a model fish predator (northern pike, Esox lucius). In response to both chemical stimuli from pike and the pike model, minnows from familiar groups showed greater shoal cohesion than those from unfamiliar groups. Tighter shoal cohesion should result in a higher probability of surviving an encounter with a predator. Fish in familiar shoals also exhibited more dashing, a known antipredator response, than those in unfamiliar groups. In addition, groups of familiar fish showed less freezing behaviour than unfamiliar groups. In response to the model fish predator, familiar shoals exhibited a greater number of predator inspections, and the number of inspectors per inspection visit was greater, than those in unfamiliar groups. These results suggest that preferential shoaling with familiar conspecifics leads to an increase in cooperative antipredator behaviour and may thereby lower a minnow's risk of predation

The dynamics of predation risk assessment: responses of anuran larvae to chemical cues of predators

1.  While the antipredator behaviour of prey has been well studied, little is known about the rules governing the predation risk assessment of prey. In this study, I measured the activity levels of predator-naive green frog ( Rana clamitans ) tadpoles during and after exposures to the chemical cue of predatory larval dragonflies ( Anax spp.). I then used the lengths of the time lags from the end of the cue exposures until the tadpoles returned to a control level of activity as an index of the perceived risk of the tadpoles. 2.  While tadpoles always responded upon exposure to the Anax chemical cue by strongly reducing their activity level, their perceived risk increased asymptotically over time during the initial period of the cue exposure. Tadpoles of all size classes perceived increasing risk in proportion to chemical cue concentration, but the length of time that tadpoles responded during cue exposure and the length of their post-exposure time lags decreased with increasing body mass. 3.  The results suggest that the perceived risk of green frog tadpoles varies over time and does not correspond directly to their behavioural response (i.e. activity level). However, their perceived risk does appear to vary in accordance with the predation risk associated with the Anax chemical cue and the reliability of the information from the cue, and therefore may be predictable.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73939/1/j.1365-2656.2008.01386.x.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/73939/2/JANE_1386_sm_Figs1.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/73939/3/JANE_1386_sm_Figs2.pd

The Evolution of Chemical Alarm Signals: Attracting Predators Benefits Alarm Signal Senders

Abstract.-A wide variety of organisms possess damage-released alarm pheromones that evoke antipredator responses in conspecifics. Understanding the evolution of such involuntary alarm signals has been perplexing because it is difficult to see direct benefits to the sender, notwith- standing benefits derived from warning relatives. Recently, it has been proposed that the alarm pheromone, or Schreckstoff, of Ostariophysan fishes may function in a fashion analogous to distress calls of many birds and mammals. The alarm pheromone may attract secondary preda- tors to the proximity of the primary predation event, and, once there, the secondary predators may disrupt the predation event, thus allowing the prey greater opportunity to escape. Previous findings have established that the alarm pheromone of fathead minnows (Pimephales promelas) attracts predators, including northern pike (Esox lucius) to an area. In this study we demonstrate that the probability that fathead minnows will escape after being captured by a northern pike is significantly increased through interference by a second pike. Taken with the previous findings that alarm pheromone attracts predators, these results are the first to provide empirical evidence of benefits to senders of an involuntary alarm signa

Coral reef fish incorporate multiple sources of visual and chemical information to mediate predation risk

Behavioural ecology is rife with examples of the way in which prey animals make decisions to alter when, where and how they forage or reproduce in response to variation in predation risk. Given that animals cannot have perfectly accurate information regarding the relative costs and benefits of each decision made, the process of decision making is fraught with uncertainty, particularly given that different sources of information will have different levels of risk associated with them. The consequence of ignoring accurate predator information is potentially death; therefore animals should have evolved the ability to incorporate multiple sources of information, extract important components from each source and respond accordingly. In this study, the anemonefish, Amphiprion percula, responded with antipredator behaviour to damage-released chemical cues from conspecifics and congenerics. However, the visual cues provided by the presence or absence of conspecifics and congenerics dramatically influenced the way in which individuals responded to chemical indicators of risk. Our results suggest that anemonefish have a complex decision-making process that incorporates multiple sources of information each with different degrees of uncertainty

Fathead minnows learn to recognize predator odour when exposed to concentrations of artificial alarm pheromone below their behavioural-response threshold

Hypoxanthine-3-N-oxide (H3NO) has been identified as the putative alarm pheromone of ostariophysan fishes. Previously we demonstrated a population-specific minimum behavioural-response threshold in fathead minnows (Pimephales promelas) to a H3NO concentration of approximately 0.4 nM. Minnows may, however, perceive low concentrations of H3NO as a predation threat, even though they do not exhibit an overt behavioural response. We conducted a series of laboratory trials to test the hypothesis that minnows can detect the alarm pheromone at concentrations below the minimum behavioural-response threshold. We exposed predator-naïve fathead minnows to H3NO at concentrations ranging from 0.4 to 0.05 nM paired with the odour of a novel predator (yellow perch, Perca flavescens) or distilled water paired with perch odour. We observed significant increases in antipredator behaviour (increased shoal cohesion, movement towards the substrate, a reduction in feeding, and an increase in the occurrence of dashing and freezing behaviour) in shoals of minnows exposed to a combined cue of 0.4 nM H3NO and perch odour (compared with a distilled-water control), but not by shoals exposed to lower concentrations of H3NO paired with perch odour or those exposed to distilled water paired with perch odour. When exposed to perch odour alone 4 days later, minnows initially conditioned to H3NO at concentrations of 0.4–0.1 nM exhibited significant increases in antipredator behaviour. These data demonstrate that minnows attend to the alarm pheromone at concentrations below the minimum behavioural-response threshold and are able to acquire the ability to recognize a novel predator even though they do not exhibit an overt behavioural response

Social learning of predators by coral reef fish: does observer number influence acquisition of information?

Prey that are capable of continuously learning the identity of new predators whilst adjusting the intensity of their responses to match their level of risk, are often at a substantive advantage. Learning about predators can occur through direct experience or through social learning from experienced individuals. Social learning provides individuals with an effective means of acquiring information while reducing the costs associated with direct learning. Under a natural setting, social learning is likely to occur between more than two individuals. As such, investigating the effect that group size has on the ability of individuals to acquire information is vital to understanding social learning dynamics. Given the characteristics of coral reefs and the biology of coral reef fishes, these habitats are an ideal medium to test whether group size affects the transmission of information. Using newly settled damselfish (Pomacentrus amboinensis), we examined whether the number of observers present influences transmission of information. We showed that: (1) predator recognition is socially transmitted from predator-experienced to predator-naïve individuals regardless of group size, and that (2) the level of response displayed by the observer does not differ following learning in different sized groups. Our study highlights that information on predator identities is able to be passed onto group members quickly without a dilution of information content

Production of chemical alarm cues in convict cichlids: the effects of diet, body condition and ontogeny

While much is known regarding the role of chemical alarm cues in the mediation of predator–prey dynamics within aquatic ecosystems, little is known regarding the production of these critically important information sources. In a series of laboratory experiments, we tested the possible effects of diet, body condition and ontogeny on the production of chemical alarm cues in juvenile convict cichlids (Archocentrus nigrofasciatus, Cichlidae, Acanthopterygii). Juvenile cichlids were fed one of two diets, tubifex worms (Tubifex spp.) or brine shrimp (Artemia spp.). Shrimp fed cichlids grew longer and heavier and were in better condition than were tubifex fed cichlids. In Experiment 1, cichlids exhibited a stronger antipredator response to conspecific skin extracts from donors fed shrimp versus tubifex, regardless of test cichlid diet. In Experiment 2, juvenile cichlids were exposed to the skin extracts of high versus low condition donors fed either tubifex or shrimp diets. Cichlids exhibited a significantly stronger antipredator response to skin extracts of high condition donors, regardless of donor diet. Finally, in Experiment 3, juvenile cichlids were exposed to skin extracts of similar sized juvenile conspecifics, adult conspecifics, swordtail (Xiphophorus helleri) or a distilled water control. We found no evidence of an ontogenetic change in the production of alarm cues as cichlids exhibited similar intensity antipredator responses when exposed to juvenile and adult conspecific alarm cues. Taken together, these data suggest that individual diet may influence body condition with the consequence of influencing chemical alarm cue production in juvenile cichlids

Coral degradation alters predator odour signatures and influences prey learning and survival

Habitat degradation is a key factor leading to the global loss of biodiversity. This problem is particularly acute in coral reef ecosystems. We investigated whether recognition of predator odours by damselfish was influenced by coral degradation and whether these changes altered survival in the wild. We taught whitespot damselfish to recognize the odour of a predator in the presence of live/healthy coral or dead/degraded coral. Fish were tested for a response to predator odours in environments that matched their conditioning environment or in environments that were mismatched. Next, we taught blue damselfish to recognize the odour of three common reef predators in live and degraded coral environments and then stocked them onto live or degraded patch reefs, where we monitored their subsequent response to predator odour along with their survival. Damselfish learned to recognize predator odours in both coral environments, but the intensity of their antipredator response was much greater when the conditioning and test environments matched. Fish released on degraded coral had about 50% higher survival if they had been trained in the presence of degraded coral rather than live coral. Altering the intensity of antipredator responses could have rather profound consequences on population growth

The response of convict cichlids to chemical alarm cues: an integrated study of behaviour, growth, and reproduction

Predation is an important agent leading to the evolution of accurate risk assessment. In fishes, one of the best studied modes of threat assessment is the use of damage release cues from consumed or damaged individuals. These cues act as sources of public information alerting both conspecific and heterospecific individuals in the immediate area of a possible predation threat. Responses to damage release cues can be behavioural (e.g. avoidance of the cue or increased schooling), morphological (e.g. change in body shape), and potentially reproductive (e.g. altered patterns of breeding and reproductive investment). In the current study we documented the response of convict cichlids (Archocentrus nigrofaciatus) to damage release cues from conspecifics, unknown heterospecifics (swordtail, Xiphophorus helleri), and distilled water. In short term behavioural trials we found that cichlids exhibited an antipredator response to injured conspecifics, while they exhibited a foraging response to injured swordtails and no response to distilled water. In longer term trials (41 days) we found that cichlids exposed to conspecific cues grew significantly less than those in the other treatments. Finally, we found that reproductive patterns were influenced by the treatments. Cichlids bred faster in the presence of predation cues (conspecific skin extract) and food cues (swordtail skin extract) than the control treatment (distilled water)