Safety signals from avoidance learning but not from yoked classical conditioning training pass both summation and retardation tests for inhibition

In one experiment half of the animals were trained to avoid a signaled footshock by jumping (30 or 160 trials), whereas the rest of the animals received the same events as yoked. For all of them the termination of the warning signal and of the shock was followed by a safety signal. Several tests were conducted to assess the ability of the stimuli to suppress licking by measuring the latency in completing 25 consecutive licks in the presence of the stimuli. Fear of the warning signal and inhibitory properties of the safety signal (summation and retardation tests) were measured. The results showed that there were no differences in fear to the warning signal, and that the safety signal behaves as a conditioned inhibitor only for animals trained with a long avoidance procedure, but not in the yoked (classical conditioning) procedure. These results highlight the role played by the avoidance response and its consequences in avoidance learning.     

Acquisition, extinction and temporal discrimination in human conditioned avoidance

Two experiments were conducted with the aim of designing a videogame for the study of human conditioned avoidance. Participants had to destroy enemy spaceships with the goal of increasing the score in a counter. Coloured signals might announce the launching of a bomb that could hit participant's spaceship producing a 30 points decrease in participant's score. Three groups of participants were trained in discriminating between a warning signal (W) and a safety signal (S) in Experiment 1. Instrumental group could avoid the loss of points by hiding the spaceship before the offset of W. Participants in the Yoked group received the same treatment received by their instrumental partners, regardless of their behaviour. In the Pavlovian group, W was always followed by the loss of points, regardless of participant's behaviour. Discrimination between W and S was better in the Instrumental groups than in the Yoked and Pavlovian control groups. Experiment 2 found extinction of avoidance when the warning signal was not followed by the bomb. Temporal discrimination was found within the participants that received the instrumental contingency in both experiments, with higher avoidance response towards the end of the warning signal. Temporal discrimination disappeared after extinction in Experiment 2.     

Characterization of radiation-induced performance decrement using a two-lever shock-avoidance task

Rats were trained to perform a task involving responses on two levers. Responding on an avoidance lever delayed the onset of electrical footshock for 20 sec and responding on a warning lever turned on a light for 60 sec. When the light was on, the task on the avoidance lever was changed from unsignaled shock avoidance to signaled shock avoidance by preceding the shocks with 5-sec warning tones. The animals preferred the signaled avoidance condition. After 100 Gy of 60Co irradiation, the animals were less able to avoid shock, an effect from which the animals recovered somewhat over 90 min. The response rate on the avoidance lever remained at or above control rates, while the response rate on the warning lever showed an initial increase, followed by a decrease below baseline. The increase in responding on the avoidance lever occurred in bursts just after presentation of the shocks. The data suggest that under these experimental conditions a subject will not respond appropriately to avoid shock or acquire cues that can facilitate the avoidance of shock. The effects, however, do not reflect an inability to perform the required movements but instead appear to reflect some characteristic of the task associated with a particular lever.     

Warning signals, receiver psychology and predator memory

This review identifies four receiver psychology perspectives that are likely to be important in the design and evolution of warning signals. Three of these perspectives (phobia, learning and prey recognition) have been studied in detail, and I include a brief review of recent work. The fourth, a memory perspective, has received little attention and is developed here. A memory perspective asks, 'how might warning signals function to reduce forgetting of avoidances between encounters?'. To answer this question I review data from psychology literature that describe important features of animal long-term memory. These data suggest that components of warning signals may function to reduce forgetting (and therefore increase memorability) by (1) preventing forgetting of learnt prey discriminations; (2) jogging the memories of forgetful predators; and (3) biasing forgetting in favour of prey avoidance when the warning signal of a defended aposematic species is copied by an edible Batesian mimic. A combination of a learning and a memory perspective suggests that the features of aposematic prey that accelerate avoidance learning may also be the features that decelerate forgetting processes. If correct, this would have important implications for the comprehension of signal design. Finally, I suggest that the cryptic appearance of an edible prey may decelerate predator learning and accelerate predator forgetting, to the benefit of the prey. In terms of learning and memory, crypsis may be an antisignal. Copyright 2000 The Association for the Study of Animal Behaviour.     

Inhibition of a conditioned reflex evoked emotional response as an "instrument" of avoidance

A method has been elaborated of training the human subjects to avoid electric shocks by overcoming the "fear" caused by a warning signal. A previously elaborated differentiated conditioned skin-galvanic response (SGR) to a sound stimulus served as a criterion of the emotional reaction. The SGR was projected on an oscilloscope screen. The electric shock was automatically delivered at the moment when the amplitude of the conditioned SGR exceeded the level marked on the screen. The subject was instructed, by overcoming the "fear", to retain the SGR amplitude below the level. If the subject succeeded in overcoming the conditioned SGR to the signal, the shock was not delivered. Since, the suppression of the conditioned SGR served as a "instrument" of avoidance and became consolidated as a habit based on a positive reinforcement. The subjects developed a stable attraction to repetition of training sessions in which they learned to suppress the "anxiety" caused by a signal of "threat".     

Trade-off between warning signal efficacy and mating success in the wood tiger moth

The coloration of species can have multiple functions, such as predator avoidance and sexual signalling, that directly affect fitness. As selection should favour traits that positively affect fitness, the genes underlying the trait should reach fixation, thereby preventing the evolution of polymorphisms. This is particularly true for aposematic species that rely on coloration as a warning signal to advertise their unprofitability to predators. Nonetheless, there are numerous examples of aposematic species showing remarkable colour polymorphisms. We examined whether colour polymorphism in the wood tiger moth is maintained by trade-offs between different functions of coloration. In Finland, males of this species have two distinct colour morphs: white and yellow. The efficacy of the warning signal of these morphs was tested by offering them to blue tits in the laboratory. Birds hesitated significantly longer to attack yellow than white males. In a field experiment, the survival of the yellow males was also higher than white males. However, mating experiments in the laboratory revealed that yellow males had lower mating success than white males. Our results offer an explanation for the maintenance of polymorphism via trade-off between survival selection and mating success.     

Do Glow‐Worm Larvae (Coleoptera: Lampyridae) Use Warning Coloration?

It is generally believed that the glowing behaviour of lampyrid larvae may be an aposematic display. Moreover, larvae of the common glow-worm ( Lampyris noctiluca ) show at least two other features, which can be used in aposematic strategies. The first is their suggestive colour pattern of yellow-pinkish lateral dots on a jet-black background and the second a possible warning odour. We performed experiments with starlings ( Sturnus vulgaris ) to test, in particular, for the significance of the colour pattern as a warning signal. Learning experiments showed that glow-worm larvae were distasteful and that starlings showed increasing avoidance of the distasteful prey through a learning process. Experiments with mimics and glow-worm larvae with obscured colours showed that starlings recognized glow-worm larvae by their colour pattern. However, there was an important effect of experience as one group of starlings that had previous contact with edible glow-worm mimics, showed delayed avoidance learning and was able to discriminate mimics from glow-worms thereafter.     

Warning Signal Efficacy: Assessing the Effects of Color,Iridescence, and Time of Day in the Field

Warning coloration deters predators from attacking distasteful or toxic prey. Signal features that influence warning color effectiveness are not well understood, and in particular, we know very little about how effective short‐wavelength and iridescent colors are as warning color elements in nature and how warning signal effectiveness changes throughout the day. We tested the effect of these factors on predation risk in nature using specimens of the distasteful pipevine swallowtail butterfly, Battus philenor. B. philenor adults display both iridescent blue and diffusely reflecting orange components in their warning signal. We painted B. philenor wings to create five different model types: all‐black, only‐iridescent‐blue, only‐orange, iridescent‐blue‐and‐orange (intact signal), and matte‐blue‐and‐orange. We placed 25 models in each of 14 replicate field sites for 72 h and checked for attacks three times each day. Model type affected the likelihood of attack; only‐orange models were, the only model attacked significantly less than the all‐black model. Iridescence did not enhance or decrease warning signal effectiveness in our experiment because matte‐blue‐and‐orange models were attacked at the same rate as iridescent‐blue‐and‐orange models. Time of day did not differentially affect model type. Video recordings of attacks revealed that insectivorous birds were responsible. The results of this experiment, when taken with previous work, indicate that the response to blue warning coloration is likely dependent on predator experience and context, but that iridescence per se does not affect warning signals in a natural context.     

Function analysis of phototropin2 using fern mutants deficient in blue light-induced chloroplast avoidance movement

Gametophytes of the fern Adiantum capillus-veneris L. were mutagenized by heavy ion beam irradiation and screened for mutants lacking chloroplast avoidance movement under high intensity blue light. Mutants recovered include several with small deletions in the AcPHOT2 gene. The avoidance movement response in these mutants could be restored by transient expression of non-mutant AcPHOT2 cDNA, indicating that the chloroplast avoidance movement in this fern is mediated by the Acphot2 protein. Further functional analyses of the Acphot2 protein were performed using this transient assay for chloroplast avoidance movement. The results obtained suggest that the LOV2, but not the LOV1, domain of Acphot2 is essential for avoidance movement, and that several residues in the C-terminus of the kinase domain contribute to the avoidance response. The rate of dark reversion of the photo-activated LOV2 domain, which was calculated photometrically, was too fast to account for the lifetime of phot2 signal estimated from physiological responses. However, the rate of dark reversion of the combined domains of LOV1 and LOV2 did correspond to the lifetime of the signal, suggesting that LOV1 might have some function in this response, although it is not essential for playing a role as a photoreceptor.     

Honest signaling and the uses of prey coloration

Abstract Although signal reliability is of fundamental importance to the understanding of animal communication, the extent of signal honesty in relation to antipredator warning signals has received relatively little attention. A recent theoretical model that assumed a physiological linkage between pigmentation and toxicity suggested that (aposematic) warning signals may often be reliable, in the sense that brightness and toxicity are positively correlated within prey populations. Two shortcomings of the model were (1) the requirement among predators for an innate aversion to brightly colored prey and (2) the assumption that prey can generate only bright coloration and not cryptic coloration. We evaluated the generality of predictions of reliable signaling when these shortcomings were removed. Without innate avoidance of bright prey, we found a positive brightness-toxin correlation when conspicuous prey coloration provided an additional fitness benefit unrelated to predation. Initially, this correlation could evolve for reasons unrelated to prey signaling; hence, aposematism might represent a striking example of exaptation. Given a choice between using pigmentation for bright or for cryptic coloration, crypsis was favored only in conditions of very low or very high resource levels. In the latter case, toxicity correlated positively with degree of cryptic coloration. Predictions of toxin-signal correlation appear robust, but we can identify interesting conditions in which signal reliability is not predicted.     

Temporal relationship between genetic and warning signal variation in the aposematic wood tiger moth (Parasemia plantaginis)

Many plants and animals advertise unpalatability through warning signals in the form of colour and shape. Variation in warning signals within local populations is not expected because they are subject to directional selection. However, mounting evidence of warning signal variation within local populations suggests that other selective forces may be acting. Moreover, different selective pressures may act on the individual components of a warning signal. At present, we have a limited understanding about how multiple selection processes operate simultaneously on warning signal components, and even less about their temporal and spatial dynamics. Here, we examined temporal variation of several wing warning signal components (colour, UV‐reflectance, signal size and pattern) of two co‐occurring colour morphs of the aposematic wood tiger moth (Parasemia plantaginis). Sampling was carried out in four geographical regions over three consecutive years. We also evaluated each morph's temporal genetic structure by analysing mitochondrial sequence data and nuclear microsatellite markers. Our results revealed temporal differences between the morphs for most signal components measured. Moreover, variation occurred differently in the fore‐ and hindwings. We found no differences in the genetic structure between the morphs within years and regions, suggesting single local populations. However, local genetic structure fluctuated temporally. Negative correlations were found between variation produced by neutrally evolving genetic markers and those of the different signal components, indicating a non‐neutral evolution for most warning signal components. Taken together, our results suggest that differential selection on warning signal components and fluctuating population structure can be one explanation for the maintenance of warning signal variation in this aposematic species.     

Fruit or aposematic insect? Context-dependent colour preferences in domestic chicks.

Colours are common stimuli in signalling systems. Requirements to function well as a signal sometimes conflict between different signallers, and the same colour stimulus is used to convey completely different messages to the same receiver. Fruits and aposematic insects both use red coloration as a signal, in the former case to signal profitability and in the latter case as a warning signal. In two experiments, we investigated whether the domestic chick, an omnivorous predator, differed in its unconditioned preference or avoidance of red and green stimuli depending on whether or not the stimulus was an insect. The experiments were designed as preference tests between red and green painted prey. The prey were live insects and artificial fruits (experiment 1), and, to investigate the effect of movement, live and dead insects (experiment 2). The chicks did not show any difference in pecking preference between red and green when fruit-like stimuli were used, but when the prey were insects, green prey were strongly preferred to red prey, and prey movement did not affect this bias. Thus, young chicks may recognize prey as insects and then discriminate between different prey colorations, or one type of food may elicit an unlearned colour preference-avoidance response that is absent with another type of food.     

Signal conflict in spider webs driven by predators and prey

Variation in the sensory physiologies of organisms can bias the receptions of signals, driving the direction of signal evolution. Sensory drive in the evolution of signals may be particularly important for organisms that confront trade-offs in signal design between the need for conspicuousness to allow effective transfer of information and the need for crypsis of the signal to unintended receivers. Several genera of orb-weaving spiders include conspicuous silk designs, stabilimenta, in the centre of their webs. Stabilimenta can be highly visible signals to predators, warning them of the presence of a noxious, sticky silk web. However, stabilimenta can also be used by prey as a signal in avoidance of webs, creating a trade-off in signal visibility. I argue that the derived spectral properties of stabilimentum silk have resulted in part from this conflict. The innate colour preferences of insects, their ability to learn colours, and the spectral properties of flowers all suggest that the reflectance spectra of stabilimenta renders them relatively cryptic to many insect prey, while maintaining their visibility to vertebrate predators.     

Film Analysis of the Tactile Communication between Cryptocentrus steinitzi (Pisces,Gobiidae) and Alpheus purpurilenticularis (Crustacea,Alpheidae)

The tactile communication between the symbiotic goby Cryptocentrus steinitzi and its burrowing shrimp partner Alpheus purpurilenticularis was investigated by film analysis. Warning signals of the goby which elicit the retreat of the shrimp into its burrow consist mainly of rapid fin flicks transmitted to the shrimp through its long antennae. Five different parameters of the structure of the warning signal were analyzed. The effect of various variables on the response of the shrimp and its latency were examined with a stepwise multiple regression analysis. Feedback mechanisms involved in this communication system are described. The evolution of the tail flick warning signal and a model describing the relationship between the main elements involved in the generation of warning signals are discussed.     

Investigating Müllerian mimicry: predator learning and variation in prey defences

Inexperienced predators are assumed to select for similarity of warning signals in aposematic species (Müllerian mimicry) when learning to avoid them. Recent theoretical work predicts that if co-mimic species have unequal defences, predators attack them according to their average unpalatability and mimicry may not be beneficial for the better defended co-mimic. In this study, we tested in a laboratory environment whether a uniform warning signal is superior to a variable one in promoting predator learning, and simultaneously whether co-mimics are preyed upon according to their average unpalatability. There was an interaction of signal variation and unpalatability but inexperienced birds did not select for signal similarity in artificial prey; when the prey was moderately defended a variable signal was even learnt faster than a uniform one. Due to slow avoidance learning, moderately defended prey had higher mortality than highly defended prey (although this was not straightforward), but mixing high and moderate unpalatability did not increase predation compared with high unpalatability. This does not support the view that predators are sensitive to varying unpalatability. The results suggest that inexperienced predators may neither strongly select for accurate Müllerian mimicry nor affect the benefits of mimicry when the co-mimics are unequally defended.     

Effect of a tryptophan lead on the swine adrenal cortex reactivity and behavioral response to stress]

Behaviour and plasma corticosteroid levels were investigated in pigs preloaded with 50 to 200 mg/kg 1-tryptophan. The treatment did not influence reactions to frustation and had no effect on continuous avoidance responding. However the adrenal response to the stress of new environment concomitant with delivery of unavoidable shocks was decreased (fig. 1), as well as the behavioural response to a fear signal superimposed on a continuous avoidance paradigm (fig. 2). These results point out relatively specific psychotropic effects of a tryptophan load in pigs.     

Linking the evolution and form of warning coloration in nature

Many animals are toxic or unpalatable and signal this to predators with warning signals (aposematism). Aposematic appearance has long been a classical system to study predator–prey interactions, communication and signalling, and animal behaviour and learning. The area has received considerable empirical and theoretical investigation. However, most research has centred on understanding the initial evolution of aposematism, despite the fact that these studies often tell us little about the form and diversity of real warning signals in nature. In contrast, less attention has been given to the mechanistic basis of aposematic markings; that is, ‘what makes an effective warning signal?’, and the efficacy of warning signals has been neglected. Furthermore, unlike other areas of adaptive coloration research (such as camouflage and mate choice), studies of warning coloration have often been slow to address predator vision and psychology. Here, we review the current understanding of warning signal form, with an aim to comprehend the diversity of warning signals in nature. We present hypotheses and suggestions for future work regarding our current understanding of several inter-related questions covering the form of warning signals and their relationship with predator vision, learning, and links to broader issues in evolutionary ecology such as mate choice and speciation.     

Premotor-Motor Interhemispheric Inhibition Is Released during Movement Initiation in Older but Not Young Adults

Neural interactions between contralateral motor regions are thought to be instrumental in the successful preparation, and execution, of volitional movements. Here we investigated whether healthy ageing is associated with a change in functional connectivity, as indicated by the ability to modulate interhemispheric interactions during movement preparation in a manner that assists rapid movement responses. Thirteen young (mean age 22.2 years) and thirteen older (68.5 years) adults rapidly abducted their left index finger as soon as possible in response to a visual imperative signal, presented 500 ms after a visual warning signal.Interactions between left dorsal premotor cortex (LPMd) and right primary motor cortex (RM1) and between left primary motor cortex (LM1) and RM1 were investigated at six time points between the warning signal and the volitional response using paired-pulse transcranial magnetic stimulation. Relative to the inhibitory interactions measured at rest, both young and older adults released LM1-RM1 inhibition beginning 250 ms after the warning signal, with no significant differences between groups. LPMd-RM1 interactions became facilitatory (from the onset of the imperative signal onwards) in the older, but not the young, group. Regression analyses revealed that for the older adults, modulation of LPMd-RM1 interactions early in the preparation period was associated with faster responses, suggesting that specifically timed modulation of these pathways may be a compensatory mechanism to offset, at least in part, slowing of motor responses. The results suggest a greater reliance on premotor regions during the preparation of simple motor actions with advancing age.