Cognition and the evolution of camouflage

Antipredator defences in motion: animals reduce predation risks by concealing or misleading motion signals

Motion is a crucial part of the natural world, yet our understanding of how animals avoid predation whilst moving remains rather limited. Although several theories have been proposed for how antipredator defence may be facilitated during motion, there is often a lack of supporting empirical evidence, or conflicting findings. Furthermore, many studies have shown that motion often 'breaks' camouflage, as sudden movement can be detected even before an individual is recognised. Whilst some static camouflage strategies may conceal moving animals to a certain extent, more emphasis should be given to other modes of camouflage and related defences in the context of motion (e.g. flicker fusion camouflage, active motion camouflage, motion dazzle, and protean motion). Furthermore, when motion is involved, defence strategies are not necessarily limited to concealment. An animal can also rely on motion to mislead predators with regards to its trajectory, location, size, colour pattern, or even identity. In this review, we discuss the various underlying antipredator strategies and the mechanisms through which they may be linked to motion, conceptualising existing empirical and theoretical studies from two perspectives - concealing and misleading effects. We also highlight gaps in our understanding of these antipredator strategies, and suggest possible methodologies for experimental designs/test subjects (i.e. prey and/or predators) and future research directions.

Adapting genetic algorithms for artificial evolution of visual patterns under selection from wild predators

Camouflage is a widespread and well-studied anti-predator strategy, yet identifying which patterns provide optimal protection in any given scenario remains challenging. Besides the virtually limitless combinations of colours and patterns available to prey, selection for camouflage strategies will depend on complex interactions between prey appearance, background properties and predator traits, across repeated encounters between co-evolving predators and prey. Experiments in artificial evolution, pairing psychophysics detection tasks with genetic algorithms, offer a promising way to tackle this complexity, but sophisticated genetic algorithms have so far been restricted to screen-based experiments. Here, we present methods to test the evolution of colour patterns on physical prey items, under selection from wild predators in the field. Our techniques expand on a recently-developed open-access pattern generation and genetic algorithm framework, modified to operate alongside artificial predation experiments. In this system, predators freely interact with prey, and the order of attack determines the survival and reproduction of prey patterns into future generations. We demonstrate the feasibility of these methods with a case study, in which free-flying birds feed on artificial prey deployed in semi-natural conditions, against backgrounds differing in three-dimensional complexity. Wild predators reliably participated in this experiment, foraging for 11 to 16 generations of artificial prey and encountering a total of 1,296 evolved prey items. Changes in prey pattern across generations indicated improvements in several metrics of similarity to the background, and greater edge disruption, although effect sizes were relatively small. Computer-based replicates of these trials, with human volunteers, highlighted the importance of starting population parameters for subsequent evolution, a key consideration when applying these methods. Ultimately, these methods provide pathways for integrating complex genetic algorithms into more naturalistic predation trials. Customisable open-access tools should facilitate application of these tools to investigate a wide range of visual pattern types in more ecologically-relevant contexts.

The evolution and ecology of multiple antipredator defences

Prey seldom rely on a single type of antipredator defence, often using multiple defences to avoid predation. In many cases, selection in different contexts may favour the evolution of multiple defences in a prey. However, a prey may use multiple defences to protect itself during a single predator encounter. Such "defence portfolios" that defend prey against a single instance of predation are distributed across and within successive stages of the predation sequence (encounter, detection, identification, approach (attack), subjugation and consumption). We contend that at present, our understanding of defence portfolio evolution is incomplete, and seen from the fragmentary perspective of specific sensory systems (e.g., visual) or specific types of defences (especially aposematism). In this review, we aim to build a comprehensive framework for conceptualizing the evolution of multiple prey defences, beginning with hypotheses for the evolution of multiple defences in general, and defence portfolios in particular. We then examine idealized models of resource trade-offs and functional interactions between traits, along with evidence supporting them. We find that defence portfolios are constrained by resource allocation to other aspects of life history, as well as functional incompatibilities between different defences. We also find that selection is likely to favour combinations of defences that have synergistic effects on predator behaviour and prey survival. Next, we examine specific aspects of prey ecology, genetics and development, and predator cognition that modify the predictions of current hypotheses or introduce competing hypotheses. We outline schema for gathering data on the distribution of prey defences across species and geography, determining how multiple defences are produced, and testing the proximate mechanisms by which multiple prey defences impact predator behaviour. Adopting these approaches will strengthen our understanding of multiple defensive strategies.

Spatial memory predicts home range size and predation risk in pheasants

Most animals confine their activities to a discrete home range, long assumed to reflect the fitness benefits of obtaining spatial knowledge about the landscape. However, few empirical studies have linked spatial memory to home range development or determined how selection operates on spatial memory via the latter's role in mediating space use. We assayed the cognitive ability of juvenile pheasants (Phasianus colchicus) reared under identical conditions before releasing them into the wild. Then, we used high-throughput tracking to record their movements as they developed their home ranges, and determined the location, timing and cause of mortality events. Individuals with greater spatial reference memory developed larger home ranges. Mortality risk from predators was highest at the periphery of an individual's home range in areas where they had less experience and opportunity to obtain spatial information. Predation risk was lower in individuals with greater spatial memory and larger core home ranges, suggesting selection may operate on spatial memory by increasing the ability to learn about predation risk across the landscape. Our results reveal that spatial memory, determined from abstract cognitive assays, shapes home range development and variation, and suggests predation risk selects for spatial memory via experience-dependent spatial variation in mortality.

Evidence of Seasonal Variation in Body Color in Adults of the Parasitoid Cirrospilus pictus (Hymenoptera: Eulophidae) in Sicily, Italy

As part of the studies on the morphological color variation of insects, a case study on the seasonal body color variation of Cirrospilus pictus (Nees) (Hymenoptera: Eulophidae: Eulophinae) parasitoid of leafminers is reported. Observations were made from January 2000 to December 2003 in north-western Sicily (Italy), in relation to sex, body regions of adults and seasonal periods. Wasps parasitizing Phyllocnistis citrella Stainton (Lepidoptera: Gracillariidae) were collected from organic citrus orchards (Citrus limon L., var. "Femminello zagara bianca" and "Femminello comune"). Adults were grouped in classes: yellow males, black males, yellow females, yellow-black females and black females. The results highlighted a phenotypic pigmentation variation in the head, thorax, gaster and legs of individuals influenced by the season of sampling. Adults were yellow-green in summer months, whereas individuals with dark pigmentation were found in autumn and winter months. A correlation between color patterns and seasonal temperatures was found for both females and males. This work provides a contribution to the description of the intraspecific variability of this species, improving its identification.

Predator responses to prey camouflage strategies: a meta-analysis

Although numerous studies about camouflage have been conducted in the last few decades, there is still a significant gap in our knowledge about the magnitude of protective value of different camouflage strategies in prey detection and survival. Furthermore, the functional significance of several camouflage strategies remains controversial. Here we carried out a comprehensive meta-analysis including comparisons of different camouflage strategies as well as predator and prey types, considering two response variables: mean predator search time (ST) (63 studies) and predator attack rate (AR) of camouflaged prey (28 studies). Overall, camouflage increased the predator ST by 62.56% and decreased the AR of prey by 27.34%. Masquerade was the camouflage strategy that most increased predator ST (295.43%). Background matching and disruptive coloration did not differ from each other. Motion camouflage did not increase ST but decreases AR on prey. We found no evidence that eyespot increases ST and decreases AR by predators. The different types of predators did not differ from each other, but caterpillars were the type of prey that most influenced the magnitude of camouflage's effect. We highlight the potential evolutionary mechanisms that led camouflage to be a highly effective anti-predatory adaptation, as well as potential discrepancies or redundancies among strategies, predator and prey types.

Distinct type II opsins in the eye decode light properties for background adaptation and behavioural background preference

Crypsis increases survival by reducing predator detection. Xenopus laevis tadpoles decode light properties from the substrate to induce two responses: a cryptic coloration response where dorsal skin pigmentation is adjusted to the colour of the substrate (background adaptation) and a behavioural crypsis where organisms move to align with a specific colour surface (background preference). Both processes require organisms to detect reflected light from the substrate. We explored the relationship between background adaptation and preference and the light properties able to trigger both responses. We also analysed which retinal photosensor (type II opsin) is involved. Our results showed that these two processes are segregated mechanistically, as there is no correlation between the preference for a specific background with the level of skin pigmentation, and different dorsal retina-localized type II opsins appear to underlie the two crypsis modes. Indeed, inhibition of melanopsin affects background adaptation but not background preference. Instead, we propose pinopsin is the photosensor involved in background preference. pinopsin mRNA is co-expressed with mRNA for the sws1 cone photopigment in dorsally located photoreceptors. Importantly, the developmental onset of pinopsin expression aligns with the emergence of the preference for a white background, but after the background adaptation phenotype appears. Furthermore, white background preference of tadpoles is associated with increased pinopsin expression, a feature that is lost in premetamorphic froglets along with a preference for a white background. Thus, our data show a mechanistic dissociation between background adaptation and background preference, and we suggest melanopsin and pinopsin, respectively, initiate the two responses.

Mimicry: just wing it. Wing shape comparison between a mimicking swallowtail and its toxic model

Female eastern tiger swallowtails (Papilio glaucus) are well-known wing coloration mimics of the toxic pipevine swallowtail (Battus philenor). Given that forewing shape is an important component of butterfly flight behaviour found in unpalatable species, we hypothesized that the mimicking females also mimic the forewing shape of their poisonous model. Thus, we predicted that mimicking eastern tiger swallowtails have a more similar wing shape to their model compared with their non-mimicking conspecific morphs. In order to test this, we compared the forewing of the model with mimicking and non-mimicking eastern tiger swallowtail morphs using a standard geometric morphometrics approach. Contrary to our hypothesis, we found significant differences of forewing shape between the two species, with no overlap, regardless of the morph. However, mimicking and non-mimicking female eastern tiger swallowtails were significantly different from each other in wing shape. This indicates that either pleiotropic effects, possibly owing to wing coloration mimicry, or selection for different flight patterns in mimics informed the evolution of forewings in this species. Additionally, we found sexual dimorphism in forewing shape within each species, which supports research indicating that both sexual selection and sex-specific natural selection are important drivers in wing shape evolution.

Variable crab camouflage patterns defeat search image formation

Understanding what maintains the broad spectrum of variation in animal phenotypes and how this influences survival is a key question in biology. Frequency dependent selection - where predators temporarily focus on one morph at the expense of others by forming a "search image" - can help explain this phenomenon. However, past work has never tested real prey colour patterns, and rarely considered the role of different types of camouflage. Using a novel citizen science computer experiment that presented crab "prey" to humans against natural backgrounds in specific sequences, we were able to test a range of key hypotheses concerning the interactions between predator learning, camouflage and morph. As predicted, switching between morphs did hinder detection, and this effect was most pronounced when crabs had "disruptive" markings that were more effective at destroying the body outline. To our knowledge, this is the first evidence for variability in natural colour patterns hindering search image formation in predators, and as such presents a mechanism that facilitates phenotypic diversity in nature.

Predator personality and prey detection: inter-individual variation in responses to cryptic and conspicuous prey

Abstract

Limited attention constrains predators from engaging in cognitively demanding tasks such as searching for cryptic prey at the same time as remaining vigilant towards threats. Since finite attention can result in negative correlations between foraging and vigilance, the tendency of individual predators to focus attention on searching for cryptic prey may be correlated with other behavioural traits which reflect risk-reward trade-offs, such as consistent inter-individual variation in boldness (a personality trait describing risk-taking, defined in this study as the time taken to leave a refuge). We investigated the importance of personality in prey detection by comparing inter-individual variation in the response of three-spined sticklebacks (Gasterosteus aculeatus) to conspicuous and cryptic prey. Fish were slower to attack cryptic prey than conspicuous prey, consistent with cryptic prey being harder to detect. Despite the greater challenge involved in detecting cryptic prey, inter-individual variation in the time taken to detect prey was similar in the cryptic and conspicuous prey treatments, and was uncorrelated with boldness, which was repeatable between individuals. We also observed a positive association between the rate of attack on conspicuous prey and whether individual fish attacked cryptic prey in other trials. Our findings suggest that boldness is not related to prey detection or attention in this context. Instead, consistent differences in motivation once exploration has begun between individual predators may explain inter-individual variation in the time taken to attack both prey cryptic and conspicuous prey.

Significance statement

Using an experimental approach to manipulate the conspicuousness of prey, we show that individual fish consistently differ in their rates of attacking prey. This demonstrates that fish show “personality variation” in predatory behaviour, but these inter-individual differences were not related to the boldness of each fish (their tendency to engage in risky behaviours).

Finding a signal hidden among noise: how can predators overcome camouflage strategies?

Substantial progress has been made in the past 15 years regarding how prey use a variety of visual camouflage types to exploit both predator visual processing and cognition, including background matching, disruptive coloration, countershading and masquerade. By contrast, much less attention has been paid to how predators might overcome these defences. Such strategies include the evolution of more acute senses, the co-opting of other senses not targeted by camouflage, changes in cognition such as forming search images, and using behaviours that change the relationship between the cryptic individual and the environment or disturb prey and cause movement. Here, we evaluate the methods through which visual camouflage prevents detection and recognition, and discuss if and how predators might evolve, develop or learn counter-adaptations to overcome these.

This article is part of the theme issue ‘Signal detection theory in recognition systems: from evolving models to experimental tests'.

Von Uexküll Revisited: Addressing Human Biases in the Study of Animal Perception

More than 100 years ago, the biologist Jakob von Uexküll suggested that, because sensory systems are diverse, animals likely inhabit different sensory worlds (umwelten) than we do. Since von Uexküll, work across sensory modalities has confirmed that animals sometimes perceive sensory information that humans cannot, and it is now well-established that one must account for this fact when studying an animal's behavior. We are less adept, however, at recognizing cases in which non-human animals may not detect or perceive stimuli the same way we do, which is our focus here. In particular, we discuss three ways in which our own perception can result in misinformed hypotheses about the function of various stimuli. In particular, we may (1) make untested assumptions about how sensory information is perceived, based on how we perceive or measure it, (2) attribute undue significance to stimuli that we perceive as complex or striking, and (3) assume that animals divide the sensory world in the same way that we as scientists do. We discuss each of these biases and provide examples of cases where animals cannot perceive or are not attending to stimuli in the same way that we do, and how this may lead us to mistaken assumptions. Because what an animal perceives affects its behavior, we argue that these biases are especially important for researchers in sensory ecology, cognition, and animal behavior and communication to consider. We suggest that studying animal umwelten requires integrative approaches that combine knowledge of sensory physiology with behavioral assays.

Multicomponent structures in camouflage and mimicry in butterfly wing patterns

Understanding how morphological structures are built is essential for appreciating the morphological complexity and divergence of organisms. One representative case of morphological structures is the camouflage and mimicry of butterfly wing patterns. Some previous studies have questioned whether camouflage and mimicry are truly structures, considering that they rely on coloration. Nevertheless, our recent study revealed that the leaf pattern of Kallima inachus butterfly wings evolved through the combination of changes in several pigment components in a block-wise manner; it remains unclear whether such block-wise structures are common in other cases of camouflage and mimicry in butterflies and how they come about. Previous studies focused solely on a set of homologous components, termed the nymphalid ground plan. In the present study, we extended the scope of the description of components by including not only the nymphalid ground plan but also other common components (i.e., ripple patterns, dependent patterns, and color fields). This extension allowed us to analyze the combinatorial building logic of structures and examine multicomponent structures of camouflage and mimicry in butterfly wing patterns. We investigated various patterns of camouflage and mimicry (e.g., masquerade, crypsis, Müllerian mimicry, Batesian mimicry) in nine species and decomposed them into an assembly of multiple components. These structural component analyses suggested that camouflage and mimicry in butterfly wing patterns are built up by combining multiple types of components. We also investigated associations between components and the kinds of camouflage and mimicry. Several components are statistically more often used to produce specific types of camouflage or mimicry. Thus, our work provides empirical evidence that camouflage and mimicry patterns of butterfly wings are mosaic structures, opening up a new avenue of studying camouflage, and mimicry from a structural perspective.

A unique camouflaged mimarachnid planthopper from mid-Cretaceous Burmese amber

Predation is a major driving force for the evolution of functional forms. Avoidance of visual predators has resulted in different kinds of anti-predator defences, such as: camouflage, crypsis, disruptive coloration, and masquerade or mimesis. Camouflage is one of the forms involving shape, colouration, structure and behaviour when the visual pattern and orientation of an animal can determine whether it lives or dies. Inferring the behaviour and function of an ancient organism from its fossilised remains is a difficult task, but in many cases it closely resembles that of its descendants on uniformitarian grounds. Here we report and discuss examples of morphological and behavioural traits involving camouflage named recently as a flatoidinisation syndrome, shown by the inclusion of a planthopper in mid-Cretaceous Burmese amber. We found a new genus and species of an extinct Cretaceous planthopper family Mimarachnidae showing peculiar complex morphological adaptations to camouflage it on tree bark. Due to convergence, it resembles an unrelated tropiduchid planthopper from Eocene Baltic amber and also a modern representatives of the planthopper family Flatidae. Flattening of the body, the horizontal position of the tegmina at repose, tegmina with an undulating margin and elevated, wavy longitudinal veins, together with colouration and more sedentary behavioral traits enable these different insects to avoid predators. Our discovery reveals flatoidinisation syndrome in mid-Cretaceous Burmese amber which may provide insights into the processes of natural selection and evolution in this ancient forest.

Processing bias: extending sensory drive to include efficacy and efficiency in information processing

Communication signals often comprise an array of colours, lines, spots, notes or odours that are arranged in complex patterns, melodies or blends. Receiver perception is assumed to influence preference and thus the evolution of signal design, but evolutionary biologists still struggle to understand how perception, preference and signal design are mechanistically linked. In parallel, the field of empirical aesthetics aims to understand why people like some designs more than others. The model of processing bias discussed here is rooted in empirical aesthetics, which posits that preferences are influenced by the emotional system as it monitors the dynamics of information processing and that attractive signals have effective designs that maximize information transmission, efficient designs that allow information processing at low metabolic cost, or both. We refer to the causal link between preference and the emotionally rewarding experience of effective and efficient information processing as the processing bias, and we apply it to the evolutionary model of sensory drive. A sensory drive model that incorporates processing bias hypothesizes a causal chain of relationships between the environment, perception, pleasure, preference and ultimately the evolution of signal design, both simple and complex.

Plasticity for colour adaptation in vertebrates explained by the evolution of the genes pomc, pmch and pmchl

Different camouflages work best with some background matching colour. Our understanding of the evolution of skin colour is based mainly on the genetics of pigmentation ("background matching"), with little known about the evolution of the neuroendocrine systems that facilitate "background adaptation" through colour phenotypic plasticity. To address the latter, we studied the evolution in vertebrates of three genes, pomc, pmch and pmchl, that code for α-MSH and two melanin-concentrating hormones (MCH and MCHL). These hormones induce either dispersion/aggregation or the synthesis of pigments. We find that α-MSH is highly conserved during evolution, as is its role in dispersing/synthesizing pigments. Also conserved is the three-exon pmch gene that encodes MCH, which participates in feeding behaviours. In contrast, pmchl (known previously as pmch), is a teleost-specific intron-less gene. Our data indicate that in zebrafish, pmchl-expressing neurons extend axons to the pituitary, supportive of an MCHL hormonal role, whereas zebrafish and Xenopus pmch+ neurons send axons dorsally in the brain. The evolution of these genes and acquisition of hormonal status for MCHL explain different mechanisms used by vertebrates to background-adapt.

Widespread Occurrence of Black-Orange-Black Color Pattern in Hymenoptera

Certain color patterns in insects show convergent evolution reflecting potentially important biological functions, for example, aposematism and mimicry. This phenomenon has been most frequently documented in Lepidoptera and Coleoptera, but has been less well investigated in Hymenoptera. It has long been recognized that many hymenopterans, especially scelionids (Platygastridae), show a recurring pattern of black head, orange/red mesosoma, and black metasoma (BOB coloration). However, the taxonomic distribution of this striking color pattern has never been documented across the entire order. The main objective of our research was to provide a preliminary tabulation of this color pattern in Hymenoptera, through examination of museum specimens and relevant literature. We included 11 variations of the typical BOB color pattern but did not include all possible variations. These color patterns were found in species belonging to 23 families of Hymenoptera, and was most frequently observed in scelionids, evaniids, and mutillids, but was relatively infrequent in Cynipoids, Diaprioids, Chalcidoids, and Apoids. The widespread occurrence of this color pattern in Hymenoptera strongly suggests convergent evolution and a potentially important function. The BOB color pattern was found in species from all biogeographic regions and within a species it was usually present in both sexes (with a few notable exceptions). In better studied tropical regions, such as Costa Rica, this color pattern was more common in species occurring at lower elevations (below 2,000 m). The biology of the tabulated taxa encompasses both ecto- and endoparasitoids, idiobionts and koinobionts, from a diversity of hosts, as well as phytophagous sawflies.

Grow Smart and Die Young: Why Did Cephalopods Evolve Intelligence?

Intelligence in large-brained vertebrates might have evolved through independent, yet similar processes based on comparable socioecological pressures and slow life histories. This convergent evolutionary route, however, cannot explain why cephalopods developed large brains and flexible behavioural repertoires: cephalopods have fast life histories and live in simple social environments. Here, we suggest that the loss of the external shell in cephalopods (i) caused a dramatic increase in predatory pressure, which in turn prevented the emergence of slow life histories, and (ii) allowed the exploitation of novel challenging niches, thus favouring the emergence of intelligence. By highlighting convergent and divergent aspects between cephalopods and large-brained vertebrates we illustrate how the evolution of intelligence might not be constrained to a single evolutionary route.

Stereopsis in animals: evolution, function and mechanisms

Stereopsis is the computation of depth information from views acquired simultaneously from different points in space. For many years, stereopsis was thought to be confined to primates and other mammals with front-facing eyes. However, stereopsis has now been demonstrated in many other animals, including lateral-eyed prey mammals, birds, amphibians and invertebrates. The diversity of animals known to have stereo vision allows us to begin to investigate ideas about its evolution and the underlying selective pressures in different animals. It also further prompts the question of whether all animals have evolved essentially the same algorithms to implement stereopsis. If so, this must be the best way to do stereo vision, and should be implemented by engineers in machine stereopsis. Conversely, if animals have evolved a range of stereo algorithms in response to different pressures, that could inspire novel forms of machine stereopsis appropriate for distinct environments, tasks or constraints. As a first step towards addressing these ideas, we here review our current knowledge of stereo vision in animals, with a view towards outlining common principles about the evolution, function and mechanisms of stereo vision across the animal kingdom. We conclude by outlining avenues for future work, including research into possible new mechanisms of stereo vision, with implications for machine vision and the role of stereopsis in the evolution of camouflage.

Summary: Stereopsis has evolved independently in different animals. We review the various functions it serves and the variety of mechanisms that could underlie stereopsis in different species.

Camouflage strategies interfere differently with observer search images

Numerous animals rely on camouflage for defence. Substantial past work has identified the presence of multiple strategies for concealment, and tested the mechanisms underpinning how they work. These include background matching, D-RUP coloration to destroy target edges, and distractive markings that may divert attention from key target features. Despite considerable progress, work has focused on how camouflage types prevent initial detection by naive observers. However, predators will often encounter multiple targets over time, providing the opportunity to learn or focus attention through search images. At present, we know almost nothing about how camouflage types facilitate or hinder predator performance over repeated encounters. Here, we use experiments with human subjects searching for targets on touch screens with different camouflage strategies, and control the experience that subjects have with target types. We show that different camouflage strategies affect how subjects improve in detecting targets with repeated encounters, and how performance in detection of one camouflage type depends on experience of other strategies. In particular, disruptive coloration is effective at preventing improvements in camouflage breaking during search image formation, and experience with one camouflage type (distraction) can decrease the ability of subjects to switch to and from search images for new camouflage types (disruption). Our study is, to our knowledge, the first to show how the success of camouflage strategies depends on how they prevent initial and successive detection, and on predator experience of other strategies. This has implications for the evolution of prey phenotypes, how we assess the efficacy of defences, and predator-prey dynamics.

Testing the feasibility of the startle-first route to deimatism

Many prey species perform deimatic displays that are thought to scare or startle would-be predators, or elicit other reflexive responses that lead to attacks being delayed or abandoned. The form of these displays differs among species, but often includes prey revealing previously-hidden conspicuous visual components. The evolutionary route(s) to deimatism are poorly understood, but it has recently been suggested that the behavioural component of the displays evolves first followed by a conspicuous visual component. This is known as the “startle-first hypothesis”. Here we use an experimental system in which naïve domestic chicks forage for artificial deimatic prey to test the two key predictions of this hypothesis: (1) that movement can deter predators in the absence of conspicuously coloured display components; and, (2) that the combination of movement and conspicuously coloured display components is more effective than movement alone. We show that both these predictions hold, but only when the movement is fast. We thus provide evidence for the feasibility of ‘the startle-first hypothesis’ of the evolution of deimatism.

Chewing Holes for Camouflage

Camouflaged objects are harder to detect if the background itself is more heterogeneous, and search becomes increasingly inefficient when the scene contains multiple items resembling the target. Some adult leaf beetles (Coleoptera: Chrysomelidae) with highly specialized habits make holes on host plant leaves while feeding. We propose that leaf beetles camouflage themselves with their feeding holes. The presence of holes makes predators' visual search harder, thus giving beetles more time to escape from the leaf surface either by jumping (Galerucinae: Alticini) or rolling (rest of Chrysomelidae). Based on behavioral observations and analysis of 25 photographs of feeding leaf beetles (15 species), we demonstrate that adult leaf beetles camouflage themselves by creating holes of uniform size, approximately half of the beetle body size. Observation of the feeding behavior and anatomy of a typical hole-feeding beetle (Altica cirsicola) showed that the foregut volume and head-prothorax mobility of beetles are the two major factors that constrain the hole size. A computer-simulated visual search test showed that the greater the number of holes, and the more each hole approached beetle body size, the longer it took humans (as models) to locate a beetle on a leaf. This study reports a newly discovered kind of camouflage, hole-feeding camouflage, in leaf beetles, which makes visual detection or recognition more difficult by changing the environmental background. This type of camouflage may open up a range of new possibilities for studies in animal cognition analysis and evolution of anti-predation defenses.

Dynamic masquerade with morphing three-dimensional skin in cuttlefish

Masquerade is a defence tactic in which a prey resembles an inedible or inanimate object thus causing predators to misclassify it. Most masquerade colour patterns are static although some species adopt postures or behaviours to enhance the effect. Dynamic masquerade in which the colour pattern can be changed is rare. Here we report a two-step sensory process that enables an additional novel capability known only in cuttlefish and octopus: morphing three-dimensional physical skin texture that further enhances the optical illusions created by coloured skin patterns. Our experimental design incorporated sequential sensory processes: addition of a three-dimensional rock to the testing arena, which attracted the cuttlefish to settle next to it; then visual processing by the cuttlefish of physical textures on the rock to guide expression of the skin papillae, which can range from fully relaxed (smooth skin) to fully expressed (bumpy skin). When a uniformly white smooth rock was presented, cuttlefish moved to the rock and deployed a uniform body pattern with mostly smooth skin. When a rock with small-scale fragments of contrasting shells was presented, the cuttlefish deployed mottled body patterns with strong papillae expression. These robust and reversible responses indicate a sophisticated visual sensorimotor system for dynamic masquerade.

Visual Ecology and the Development of Visually Guided Behavior in the Cuttlefish

Cuttlefish are highly visual animals, a fact reflected in the large size of their eyes and visual-processing centers of their brain. Adults detect their prey visually, navigate using visual cues such as landmarks or the e-vector of polarized light and display intense visual patterns during mating and agonistic encounters. Although much is known about the visual system in adult cuttlefish, few studies have investigated its development and that of visually-guided behavior in juveniles. This review summarizes the results of studies of visual development in embryos and young juveniles. The visual system is the last to develop, as in vertebrates, and is functional before hatching. Indeed, embryonic exposure to prey, shelters or complex background alters postembryonic behavior. Visual acuity and lateralization, and polarization sensitivity improve throughout the first months after hatching. The production of body patterning in juveniles is not the simple stimulus-response process commonly presented in the literature. Rather, it likely requires the complex integration of visual information, and is subject to inter-individual differences. Though the focus of this review is vision in cuttlefish, it is important to note that other senses, particularly sensitivity to vibration and to waterborne chemical signals, also play a role in behavior. Considering the multimodal sensory dimensions of natural stimuli and their integration and processing by individuals offer new exciting avenues of future inquiry.

Size Matters: Observed and Modeled Camouflage Response of European Cuttlefish (Sepia officinalis) to Different Substrate Patch Sizes during Movement

Camouflage is common throughout the phylogenetic tree and is largely used to minimize detection by predator or prey. Cephalopods, and in particular Sepia officinalis cuttlefish, are common models for camouflage studies. Predator avoidance behavior is particularly important in this group of soft-bodied animals that lack significant physical defenses. While previous studies have suggested that immobile cephalopods selectively camouflage to objects in their immediate surroundings, the camouflage characteristics of cuttlefish during movement are largely unknown. In a heterogenic environment, the visual background and substrate feature changes quickly as the animal swim across it, wherein substrate patch is a distinctive and high contrast patch of substrate in the animal's trajectory. In the current study, we examine the effect of substrate patch size on cuttlefish camouflage, and specifically the minimal size of an object for eliciting intensity matching response while moving. Our results indicated that substrate patch size has a positive effect on animal's reflectance change, and that the threshold patch size resulting in camouflage response falls between 10 and 19 cm (width). These observations suggest that the animal's length (7.2–12.3 cm mantle length in our case) serves as a possible threshold filter below which objects are considered irrelevant for camouflage, reducing the frequency of reflectance changes—which may lead to detection. Accordingly, we have constructed a computational model capturing the main features of the observed camouflaging behavior, provided for cephalopod camouflage during movement.

Camouflage

Nokelainen and Stevens introduce strategies of concealment among animals and plants.