The role of numerical competence in a specialized predatory strategy of an araneophagic spider

Although a wide range of vertebrates have been considered in research on numerical competence, little is known about the role of number-related decisions in the predatory strategies of invertebrates. Here, we investigate how numerical competence is expressed in a highly specialized predatory strategy adopted by the small juveniles of Portia africana when practicing communal predation, with the prey being another spider, Oecobius amboseli. Two or more P. africana juveniles sometimes settle by the same oecobiid nest and then share the meal after one individual captures the oecobiid. Experiments were designed to clarify how these predators use number-related cues in conjunction with non-numerical cues when deciding whether to settle at a nest. We used lures (dead spiders positioned in lifelike posture) arranged in a series of 24 different scenes defined by the type, configuration and especially number of lures. On the whole, our findings suggest that P. africana juveniles base settling decisions on the specific number of already settled conspecific juveniles at the nest and express a preference for settling when the number is one instead of zero, two or three. By varying the size of the already settled juveniles and their positions around the nest, we show that factors related to continuous variables and stimulus configuration are unlikely explanations for our findings.     

Prey behaviour across antipredator adaptation types: how does growth trajectory influence learning of predators?

Despite the fact that the ability of animals to avoid being consumed by predators is influenced by their behaviour, morphology and life history, very few studies have attempted to integrate prey responses across these adaptation types. Here, our goal was to address the link between life-history traits (size and growth trajectory) of tadpoles and behavioural responses to predators. Specifically, we wanted to determine whether information learned about predators was influenced by prey growth trajectory before and after learning. We manipulated the size/growth trajectory of tadpoles by raising them under different temperatures. Tadpoles raised on a slow-growth trajectory (under cold conditions) and taught to recognize a salamander subsequently showed stronger responses after 2 weeks than tadpoles that were raised on a fast-growth trajectory (under warm conditions). When we account for the effect of size (r ² = 0.22) on the responses of prey to predator cues, we find that the growth trajectory pre-learning but not post-learning influences the learned responses of the tadpoles. The differences in responses to predators may reflect differential memory associated with the predator. To our knowledge, this is the first study that has attempted to link life-history traits (size and growth rate) with learning of predators. In order to gain a comprehensive understanding of antipredator responses of prey animals, we call for additional integrative studies that examine prey anti-predator responses across adaptation types.     

Friend or foe? The role of latent inhibition in predator and non-predator labelling by coral reef fishes

In communities of high biodiversity, the ability to distinguish predators from non-predators is crucial for prey success. Learning often plays a vital role in the ability to distinguish species that are threatening from those that are not. Many prey animals learn to recognise predators based on a single conditioning event whereby they are exposed to the unknown predator at the same time as alarm cues released from injured conspecifics. The remarkable efficiency of such learning means that recognition mistakes may occur if prey inadvertently learn that a species is a predator when it is not. Latent inhibition is a means by which prey that are pre-exposed to an unknown species in the absence of negative reinforcement can learn that the unknown animal is likely not a threat. Learning through latent inhibition should be conservative because mistakenly identifying predators as non-predators can have fatal consequences. In this study, we demonstrated that a common coral reef fish, lemon damselfish, Pomacentrus moluccensis can learn to recognise a predator as non-threatening through latent inhibition. Furthermore, we showed that we could override the latent inhibition effect by conditioning the prey to recognise the predator numerous times. Our results highlight the ability of prey fish to continually update the information regarding the threat posed by other fishes in their vicinity.     

Learning, memorizing and apparent forgetting of chemical cues from new predators by Iberian green frog tadpoles

Many antipredator adaptations are induced by the prey’s ability to recognize chemical cues from predators. However, predator recognition often requires learning by prey individuals. Iberian green frog tadpoles (Pelophylax perezi) have the ability to learn new potential predators. Here, we tested the memory capabilities of Iberian green frog tadpoles. We conditioned tadpoles with chemicals cues from a non-predatory fish in conjunction with conspecific alarm cues, and examined whether tadpoles retained their conditioned response (reduction of activity level). We found that conditioned tadpoles reduced their activity levels in subsequent exposures to the non-predatory fish cues alone. Tadpoles were able to remember this association and reduced movement rate at least for 9 days after. The ability to learn and memorize potential predators may be especially important for the survivorship of prey species that are likely to find a high variety of predators. However, after those 9 days, there was a lack of response to the non-predatory fish cues alone in the absence of reinforcement. This could be explained if tadpoles behave according to the threat-sensitive predator avoidance hypothesis, and the perceived risk to the learning cue diminished over time, or it could be due to an apparent forgetting process to avoid non-adaptative responses to chemical cues of non-dangerous species that were randomly paired with alarm cues. Thus, this study demonstrates that green frog tadpoles in the absence of reinforcement remember the chemical cues of a learned predator only for a limited time that may be adaptative in a threat-sensitive context.     

Specialised use of working memory by Portia africana,a spider-eating salticid

Using expectancy–violation methods, we investigated the role of working memory in the predatory strategy of Portia africana, a salticid spider from Kenya that preys by preference on other spiders. One of this predator’s tactics is to launch opportunistic leaping attacks on to other spiders in their webs. Focussing on this particular tactic, our experiments began with a test spider on a ramp facing a lure (dead prey spider mounted on a cork disc) that could be reached by leaping. After the test spider faced the lure for 30 s, we blocked the test spider’s view of the lure by lowering an opaque shutter before the spider leapt. When the shutter was raised 90 s later, either the same lure came into view again (control) or a different lure came into view (experimental: different prey type in same orientation or same prey type in different orientation). We recorded attack frequency (number of test spiders that leapt at the lure) and attack latency (time elapsing between shutter being raised and spiders initiating a leap). Attack latencies in control trials were not significantly different from attack latencies in experimental trials, regardless of whether it was prey type or prey orientation that changed in the experimental trials. However, compared with test spiders in the no-change control trials, significantly fewer test spiders leapt when prey type changed. There was no significant effect on attack frequency when prey orientation changed. These findings suggest that this predator represents prey type independently of prey orientation.     

Anuran tadpoles learn to recognize injury cues from members of the same prey guild

Recognition of predation risk from cues released from injured heterospecific could be beneficial when prey belongs to the same prey guild. Here, we performed three experiments. Experiment 1 showed that P. thaul tadpoles reduced their activity levels when exposed to conspecific injury cues, but not when exposed to amphipod injury cues. Experiment 2 tested whether P. thaul tadpoles can learn to recognize predation risk from chemical cues released from injured heterospecifics from the same prey guild (amphipod, Hyalella patagonica). A group of tadpoles were conditioned by exposing them to a specific concentration of amphipod injury cues paired with conspecific injury cues. Two days later, we evaluated changes in the activity of tadpoles when they were exposed to amphipod cues. As a control of learning, we used an unpaired group. Additionally, we used more control groups to fully investigate the learning mechanism. Our results showed that tadpoles can learn to recognize predation risk from injured amphipods and that the mechanism underlying the observed learned response could be associative. Experiment 3 replicated Experiment 2 and also showed that a low concentration of amphipod cues did not sustain that learning.     

ERP correlates of attentional processing in spider fear: evidence of threat-specific hypervigilance

Attentional bias towards threat can be demonstrated by enhanced processing of threat-related targets and/or greater interference when threat-related distractors are present. These effects are argued to reflect processing within the orienting and executive control networks of the brain respectively. This study investigated behavioural (RT) and electrophysiological correlates of early selective attention and top-down attentional control among females with high (n?=?16) or low (n?=?16) spider fear (Mean age?=?22 years). Participants completed a novel flanker go/nogo task in which a central schematic flower or spider stimulus was flanked by either congruent or incongruent distractors. Participants responded to green stimuli (go trials) and withheld response to yellow stimuli (nogo trials). High fear participants demonstrated significantly shorter reaction times and greater P1 amplitude to spider targets, suggesting specific hypervigilance towards threat-relevant stimuli. In contrast to predictions, there was little evidence for behavioural interference effects or differences in N2 amplitude when distractor stimuli were threat-relevant.     

One-encounter search-image formation by araneophagic spiders

An experimental study of search-image use by araneophagic jumping spiders (i.e., salticid spiders that prey routinely on other spiders) supports five conclusions. First, araneophagic salticids have an innate predisposition to form search images for specific prey from their preferred prey category (spiders) rather than for prey from a non-preferred category (insects). Second, single encounters are sufficient for forming search images. Third, search images are based on selective attention specifically to optical cues. Fourth, there are trade-offs in attention during search-image use (i.e., forming a search image for one type of spider diminishes the araneophagic salticids attention to other spiders). Fifth, the araneophagic salticids adoption of search images is costly to the prey (i.e., when the araneophagic salticid adopts a search, the preys prospects for surviving encounters with the araneophagic salticid are diminished). Cognitive and ecological implications of search-image use are discussed.     

Memory of captured prey in three web spiders (Araneae: Araneidae, Linyphiidae, Tetragnathidae)

We gave three web spiders, Argiope argentata (Araneidae), Nephila clavipes (Tetragnathidae) and Neriene peltata (Linyphiidae), large and small prey which we then removed from the spiders’ webs. Following prey removal the spiders searched by walking around the web and pulling on its threads for several minutes, stopping when allowed to find the prey. Spiders that captured larger prey searched for longer. Searching behaviour was different from the spiders’ responses to disturbance and did not appear to be elicited by proximal cues. Instead, the spiders formed memories of captured prey that included details about prey size and freshness. Received: 3 March 2000 / Accepted after revision: 24 July 2000     

Deliberate real-time mood regulation in adulthood: The importance of age,fixation and attentional functioning

While previous research has linked executive attention to emotion regulation, the current study investigated the role of attentional alerting (i.e., efficient use of external warning cues) on younger (N=39) and older (N=44) adults’ use of gaze to regulate their mood in real time. Participants viewed highly arousing unpleasant images while reporting their mood and were instructed to deliberately manage how they felt and to minimise the effect of those stimuli on their mood. Fixations toward the most negative areas of the images were recorded with eye tracking. We examined whether looking less at the most negative regions, compared to each individual's own tendency, was a beneficial mood regulatory strategy and how it interacted with age and alerting ability. High alerting older adults, who rely more on external cues to guide their attention, experienced a smaller decline in mood over time by activating a less-negative-looking approach (compared to their own average tendency), effectively looking away from the most negative areas of the images. More negative gaze patterns predicted better mood for younger adults, though this effect decreased over time. Alerting did not moderate gaze–mood links in younger adults. Successful mood regulation may thus depend on particular combinations of age, fixation, and attention.     

Learning about non-predators and safe places: the forgotten elements of risk assessment

A fundamental prerequisite for prey to avoid being captured is the ability to distinguish dangerous stimuli such as predators and risky habitats from non-dangerous stimuli such as non-predators and safe locations. Most research to date has focused on mechanisms allowing prey to learn to recognize risky stimuli. The paradox of learned predator recognition is that its remarkable efficiency leaves room for potentially costly mistakes if prey inadvertently learn to recognize non-predatory species as dangerous. Here, we pre-exposed embryonic woodfrogs, Rana sylvatica, to the odour of a tiger salamander, Ambystoma tigrinum, without risk reinforcement, and later try to teach the tadpoles to recognize the salamander, a red-bellied newt Cynops pyrrhogaster—a closely related amphibian, or a goldfish, Carassius auratus, as a predator. Tadpoles were then tested for their responses to salamander, newt or fish odour. Pre-exposure to salamander did not affect the ability of tadpoles to learn to recognize goldfish as a predator. However, the embryonic pre-exposure to salamanders inhibited the subsequent learning of salamanders as a potential predator, through a mechanism known as latent inhibition. The embryonic pre-exposure also prevented the learned recognition of novel newts, indicating complete generalization of non-predator recognition. This pattern does not match that of generalization of predator recognition, whereby species learning to recognize a novel predator do respond, but not as strongly, to novel species closely related to the known predator. The current paper discusses the costs of making recognition mistakes within the context of generalization of predators and dangerous habitats versus generalization of non-predators and safe habitats and highlights the asymmetry in which amphibians incorporate information related to safe versus risky cues in their decision-making. Mechanisms such as latent inhibition allow a variety of prey species to collect information about non-threatening stimuli, as early as during their embryonic development, and to use this information later in life to infer the danger level associated with the stimuli.     

Different chemical cues originating from a shared predator induce common defense responses in two prey species

In freshwater ecosystems, inducible defenses that involve behavioral or morphological changes in response to chemical cue detection are key phenomena in prey–predator interactions. Many species with different phylogenetic and ecological traits (e.g., general activity patterns and microhabitats) use chemical cues to avoid predators. We hypothesized that prey species with a shared predator, but having different ecological traits, would be adapted to detect different chemical cues from the predator. However, the proximate mechanisms by which prey use chemical cues to avoid predation remain little known. Here, we tested our hypothesis by using fractionated chemical components from predatory dragonfly nymphs (Lesser Emperor, Anax parthenope julius) to trigger anti-predator behavioral responses in two anuran tadpoles, the wrinkled frog Glandirana (Rana) rugosa and the Japanese tree frog Hyla japonica. Glandirana rugosa detected chemical cues that had either high or low hydrophobic properties, but H. japonica responded only to chemical cues with hydrophilic properties. During the normal behaviors of these tadpole species, G. rugosa remains immobile in benthic habitats, whereas H. japonica exhibits active swimming at the surface or in the middle of the water column. As we had hypothesized, these tadpole species, which have different general activity levels and microhabitats, detected different chemical cues that were exuded by their shared predator and responded by changing their activities to avoid predation. The specific chemical cues detected by each tadpole species are likely to have characteristics that optimize effective predator detection and encounter avoidance of the shared dragonfly predator.     

Investigating the Constrained Action Hypothesis: A Movement Coordination and Coordination Variability Approach

The purpose of this study was to examine the effects of focus of attention cues on movement coordination and coordination variability in the lower extremity. Twenty participants performed the standing long jump under both internal and external focus of attention conditions. A modified vector coding technique was used to evaluate the influence of attentional focus cues on lower extremity coordination patterns and coordination variability during the jumps. Participants jumped significantly further under an external focus of attention condition compared with an internal focus of attention condition (p = .035, effect size = .29). Focus of attention also influenced coordination between the ankle and knee, F(6, 19) = 2.87, p = .012, effect size = .388, with participants primarily using their knees under the internal focus of attention, and using both their ankles and knees under the external focus of attention. Attentional focus cues did not influence ankle-knee, F(1, 19) = 0.02, p = .98, effect size = .02, or hip-knee, F(1, 19) = 5.00, p = .49, effect size = .16, coordination variability. Results suggest that while attentional focus may not directly influence movement coordination condition, there is still a change in movement strategy resulting in greater jump distances following an external focus of attention.     

The role of learning in risk-avoidance strategies during spider–ant interactions

Cognitive abilities used by arthropods, particularly predators, when interacting in a natural context have been poorly studied. Two neotropical sympatric predators, the golden silk spider Nephila clavipes and the ectatommine ant Ectatomma tuberculatum, were observed in field conditions where their interactions occurred regularly due to the exploitation of the same patches of vegetation. Repeated presentations of E. tuberculatum workers ensnared in their web triggered a progressive decrease in the capture response of N. clavipes. All the spiders that stopped trying to catch the ant on the second and/or third trial were individuals that had been bitten during a previous trial. Behavioural tests in natural field conditions showed that after a single confrontation with ant biting, spiders were able to discriminate this kind of prey more quickly from a defenceless prey (fruit flies) and to selectively and completely suppress their catching response. This one-trial aversive learning was still effective after 24 h. Likewise, E. tuberculatum workers entangled once on a N. clavipes web and having succeeded in escaping, learned to escape more quickly, breaking through the web by preferentially cutting spiral threads (sticky traps) rather than radial threads (stronger structural unsticky components) or pursuing the cutting of radials but doing it more quickly. Both strategies, based on a one-trial learning capability, obviously minimize the number of physical encounters between the two powerful opponents and may enhance their fitness by diminishing the risk of potential injuries resulting from predatory interactions.     

The role of experience in web-building spiders (Araneidae)

A typical feature of vertical orb-webs is the ‘top/bottom’ asymmetry, where the lower web region is larger than the upper web region. This asymmetry may improve prey capture success, because, sitting in the hub of the web, a spider can reach prey entangled below the hub faster than prey entangled in the area above the hub. While web asymmetry is known to vary intraspecifically, we tested if this variation also exists at the individual level and whether it is the result of experience, using two orb-web spider species, Argiope keyserlingi and Larinioides sclopetarius. The results reveal that experienced web-building spiders constructed more asymmetric webs than conspecifics deprived of any prior building experience over a period of several months. Experienced individuals invested more silk material into the web region below the hub, which covered a larger area. Moreover, web asymmetry was also influenced by previous prey capture experiences, as spiders increased the lower region of the web if it intercepted the most prey over a period of 6 days. Consequently, spiders may be able to use long-term web-building experience as well as short-term prey capture experience to build better traps. In contrast to previous views of spiders, experience can contribute to intraspecific as well as to individual variations in web design. Received: 1 March 1999 / Accepted after revision: 18 August 1999     

Attentional shifts to emotionally charged cues: Behavioural and erp data

Abstract

When information activated in memory involves emotional associations, the ability to shift attention away from an emotional cue is impaired compared to an emotionally neutral cue. The purpose of the present study was to investigate how emotional stimuli modulate attentional processes, and how this is reflected in localised brain electrical activity. Eight emotion and eight neutral words served as cues in a covert attention spatial orienting task. The cues were either valid or invalid indicators of which hemifield the target would be presented to. In the remaining trials, no cue was presented prior to the target. Twenty subjects were instructed to manually respond to the target as fast as possible. Event-related potentials (ERPs) showed an enhanced P3 component to the emotion words. The ERPs to the target showed enhanced P1 and P3 components on invalid trials, with emotional cues. There were faster reaction times (RTs) to validly cued targets, but only when the emotion words served as cues. The results demonstrated that the emotional cues elicited sustained focused attention, facilitating an engage mechanism of spatial orienting.     

Attending to detail by communal spider-eating spiders

Communal predators may often need to make especially intricate foraging decisions, as a predator's success may depend on the actions of its neighbours. Here,we consider the decisions made by Portia africana, a jumping spider (Salticidae) that preys on other spiders, including Oecobius amboseli (Oecobiidae), a small prey spider that lives under small sheets of silk (nests) on the walls of buildings. P. africana juveniles settle near oecobiid nests and then ambush oecobiids as they leave or enter the nest. Two or more P. africana juveniles sometimes settle at the same nest and, when an oecobiid is captured, the P. africana juveniles may share the meal. We investigated the joining decisions made by na?ve P. africana juveniles. Experiments were based on using lures (dead spiders positioned in lifelike posture) arranged in a series of 17 different scenes defined by the presence/absence of a nest, the lure types present and the configuration of the lures and the nest. Our findings imply that P. africana juveniles make remarkably precise predatory decisions, with the variables that matter including whether a nest is present, the identity of spiders inside and outside a nest and how spiders are positioned relative to each other and the nest.     

When spiders appear suddenly: spider-phobic patients are distracted by task-irrelevant spiders

Fear is thought to facilitate the detection of threatening stimuli. Few studies have examined the effects of task-irrelevant phobic cues in search tasks that do not involve semantic categorization. In a combined reaction time and eye-tracking experiment we investigated whether peripheral visual cues capture initial attention and distract from the execution of goal-directed eye movements. Twenty-one spider-phobic patients and 21 control participants were instructed to search for a color singleton while ignoring task-irrelevant abrupt-onset distractors which contained either a small picture of a spider (phobic), a flower (non-phobic, but similar to spiders in shape), a mushroom (non-phobic, and not similar to spiders in shape), or no picture. As expected, patients' reaction times were longer on trials with spider distractors. However, eye movements revealed that this was not due to attentional capture by spider distractors; patients more often fixated on all distractors with pictures, but their reaction times were delayed by longer fixation durations on spider distractors. These data do not support automatic capture of attention by phobic cues but suggest that phobic patients fail to disengage attention from spiders.     

Committing to implementation intentions: Attention and memory effects for selected situational cues

Two studies tested whether forming implementation intentions (Gollwitzer, Am Psychol 54:493?C503 in 1999) results in a heightened activation of specified situational cues. Going beyond prior studies, participants of the present studies specified these opportunities on their own (i.e., the action cues were not assigned by the experimenter), and activation level was assessed by attraction of attention and recall performance rather than lexical decisions. In Study 1, situational cues associated with the where and when to act on an everyday life goal attracted more attention than non-specified cues when presented to the non-attended channel in a dichotic listening task. In Study 2, the recall of specified cues was better than that of non-specified cues both 15?min after forming implementation intentions and after a delay of 2?days. Importantly, goal commitment and implementation intention commitment moderated this effect.     

Prey positions as consumers' behavioural patterns: Exploratory evidence from an fMRI study

The present article reviews some of the tenets of the Consolidated Model of Financial Predation (CMFP). The CMFP is used to explain how investors behave as either predators or prey in the financial markets, for example, during the 2008 predatory‐mortgages crisis. The article tests one of its key assumptions: that is, that people adopt different levels of prey positions. In the last four years, a number of articles have been published on the CMFP, which states that people adopt either a predator or a prey position (PPP), or else a mixture of both. The model has emerged as a result of a five‐year study and has found various applications, in particular, in the field of behavioural finance. According to this model, consumers of financial products tend to position themselves as either predators or prey. In the latter case, this causes them to judge the relationship in negative terms and to experience it as less rewarding, if not punishing altogether. This has two effects: first, perceived predation tends to gain in power and second, purchasing decisions may not be optimal. Results from an exploratory functional magnetic resonance imaging (fMRI) study aimed at generating prey positions in minimal stress conditions are presented; they show that there is a significant difference between at least two prey positions, labelled “known predator–prey position” (KPPP) and “unknown predator–prey position” (UPPP). This means that consumers of financial products could potentially face two levels of apprehension (perceived predation): a high one under uncertainty and a lower one when conditions are volatile. Copyright © 2016 John Wiley & Sons, Ltd.