A fish‐eye view of cuttlefish camouflage using in situ spectrometry

Cuttlefish are colour blind yet they appear to produce colour‐coordinated patterns for camouflage. Under natural in situ lighting conditions in southern Australia, we took point‐by‐point spectrometry measurements of camouflaged cuttlefish, Sepia apama, and various natural objects in the immediate visual surrounds to quantify the degree of chromatic resemblance between cuttlefish and backgrounds to potential fish predators. Luminance contrast was also calculated to determine the effectiveness of cuttlefish camouflage to this information channel both for animals with or without colour vision. Uniform body patterns on a homogeneous background of algae showed close resemblance in colour and luminance; a Uniform pattern on a partially heterogeneous background showed mixed levels of resemblance to certain background features. A Mottle pattern with some disruptive components on a heterogeneous background showed general background resemblance to some benthic objects nearest the cuttlefish. A noteworthy observation for a Disruptive body pattern on a heterogeneous background was the wide range in spectral contrasts compared to Uniform and Mottle patterns. This suggests a shift in camouflage tactic from background resemblance (which hinders detection by the predator) to more specific object resemblance and disruptive camouflage (which retards recognition). © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 109 , 535–551.     

Threshold determination for olfactory receptors of the spiny lobster

The shallow water caridean shrimps Heptacarpus pictus and H. paludicola are polymorphic in colour pattern. Populations of these species collected over colour‐variable substrates showed the greatest degree of coloration in terms of the proportion of individuals displaying a distinct colour pattern. The frequencies of H. Pictus colour morphs varied significantly between most sampling periods. Apostatic selection by fish predators is suggested as one hypothesis which could explain these changes in morph frequency.

Experiments with Heptacarpus pictus on rapid colour change showed that, although some pigment migration did occur in the chromatosomes studied, the macroscopic appearance of the colour patterns was not altered when shrimps were shifted from black to white backgrounds or vice versa. The results of background choice experiments with H. pictus suggest that these shrimp do not seek out colour backgrounds that would seem to be a matching background in a concealing coloration. This behaviour is consistent with the morphology of the colour patterns which appears to be a disruptive coloration rather than a concealing coloration that closely matches a particular substrate.     

Crypsis in a heterogeneous environment: relationships between changeable polymorphic colour patterns and behaviour in a galaxiid fish

1. The ability to achieve optimal camouflage varies between microhabitats in heterogeneous environments, potentially restricting individuals to a single habitat or imposing a compromise on crypsis to match several habitats. However, animals may exhibit morphological and behavioural attributes that enhance crypsis in different habitats. 2. We used an undescribed fish species, Galaxias‘nebula’, to investigate two objectives. First, we examined two potential methods of enhancing crypsis: change in colour pattern and selection of a suitable background. Second, we characterised the colour pattern of this unstudied fish and assessed its capacity for crypsis. 3. No background selection was apparent but the area of dark pigment expressed varied between backgrounds, which may negate the requirement to be choosy about habitats. The capacity to change colour and selection of a background that maximises crypsis are most likely separate, non‐mutually exclusive strategies. 4. Galaxias‘nebula’ exhibits polymorphic, non‐interchangeable colour patterns that have elements of both background pattern matching and disruptive colouration. This, coupled with habitat characteristics, suggests a combination of generalist and specialist strategies of habitat use. The fish’s camouflage strategy and air‐breathing ability may be key to survival under increasing pressure from habitat degradation and invasive predators.     

The roles of colour change and behaviour in the hygrothermal balance of a littoral isopod,Ligia oceanica

Summary Ligia oceanica can change its colour using melanophores, the animal's reflectance varying between about 2 and 10%. Darker individuals heat up more quickly, and to higher body temperatures, than do pale ones. Colour change shows an underlying circadian rhythm, though the pattern of this rhythm varies with temperature, humidity, background and time of year. In general the rhythm is such as to ensure maximum camouflage at the critical dusk period, but in some conditions hygrothermal needs are overriding and the animals are paler (to stay cool) or darker (to warm up). In addition, animals show short term colour modification; when transferred to differing backgrounds and temperatures their colours initially reflect background matching, but after 30–45 min are modified into thermally appropriate shades, dark at 5° C and pale at 20° C. Field-caught specimens showed body temperatures that varied with colouration, and modification of colour in relation to thermal needs, particularly by being paler than expected when forced into the open by daytime high tides, and darker than expected when active prior to dusk. Animals invariably selected dark backgrounds in choice chambers. However, choice of humidity depended on previous experience; saturated air was normally preferred, but warm animals chose drier air (to allow evaporative cooling) unless also water-stressed. They also tended to disperse to facilitate cooling, whereas aggregation increased with increasing RH and with decreasing temperature. The interactions of colour changes, behavioural choices, and activity patterns in controlling the hygrothermal belance of Ligia in the intertidal environment are discussed in the light of these results.     

Colour plasticity and background matching in a threespine stickleback species pair

Examining differences in colour plasticity between closely‐related species in relation to the heterogeneity of background colours found in their respective habitats may offer important insight into how cryptic colour change evolves in natural populations. In the present study, we examined whether nonbreeding dorsal body coloration has diverged between sympatric species of stickleback along with changes in habitat‐specific background colours. The small, limnetic species primarily occupies the pelagic zone and the large, benthic species inhabits the littoral zone. We placed benthic and limnetic sticklebacks against extremes of habitat background colours and measured their degree of background matching and colour plasticity. Benthics matched the littoral background colour more closely than did the limnetics, although there was no difference between species in their resemblance to the pelagic background colour. Benthics were able to resemble both background colours by exhibiting greater directional colour plasticity in their dorsal body coloration than limnetics, which may be an adaptive response to the greater spectral heterogeneity of the littoral zone. The present study highlights how habitat‐specific spectral characteristics may shape cryptic coloration differences between stickleback species. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 102 , 902–914.     

Background matching ability and the maintenance of a colour polymorphism in the red devil cichlid

The evolution and maintenance of colour polymorphisms remains a topic of considerable research interest. One key mechanism thought to contribute to the coexistence of different colour morphs is a bias in how conspicuous they are to visual predators. Although individuals of many species camouflage themselves against their background to avoid predation, differently coloured individuals within a species may vary in their capacity to do so. However, to date, very few studies have explicitly investigated the ability of different colour morphs to plastically adjust their colouration to match their background. The red devil (Amphilophus labiatus) is a Neotropical cichlid fish with a stable colour polymorphism, with the gold morph being genetically dominant and having a myriad of documented advantages over the dark morph. However, gold individuals are much rarer, which may be related to their heightened conspicuousness to would‐be predators. Here, we tested the ability of differently coloured individuals to phenotypically adjust the shade of their body colour and patterns to match their background. In particular, we filmed dark, gold and mottled (a transitioning phase from dark to gold) individuals under an identical set‐up on light vs. dark‐coloured substrates. We found that, in contrast to individuals of the dark morph, gold and mottled individuals were less capable of matching their body colouration to their background. As a result, gold individuals appeared to be more conspicuous. These results suggest that a difference in background matching ability could play an important role in the maintenance of colour polymorphisms.     

Rockpool Gobies Change Colour for Camouflage

Camouflage is found in a wide range of species living in numerous habitat types, offering protection from visually guided predators. This includes many species from the intertidal zone, which must cope with background types diverse in appearance and with multiple predator groups foraging at high and low tide. Many animals are capable of either relatively slow (hours, days, weeks) or rapid (seconds and minutes) colour change in order to better resemble the background against which they are found, but most work has been restricted to a few species or taxa. It is often suggested that many small intertidal fish are capable of colour change for camouflage, yet little experimental work has addressed this. Here, we test rock gobies (Gobius paganellus) for colour change abilities, and whether they can tune their appearance to match the background. In two experiments, we place gobies on backgrounds of different brightness (black or white), and of different colours (red and blue) and use digital image analysis and modelling of predator (avian) vision to quantify colour and luminance (perceived lightness) changes and camouflage. We find that gobies are capable of rapid colour change (occurring within one minute), and that they can change their luminance on lighter or darker backgrounds. When presented on backgrounds of different colours, gobies also change their colour (hue and saturation) while keeping luminance the same. These changes lead to predicted improvements in camouflage match to the background. Our study shows that small rockpool fish are capable of rapid visual change for concealment, and that this may be an important mechanism in many species to avoid predation, especially in complex heterogeneous environments.     

Sexually dimorphic melanin‐based colour polymorphism,feather melanin content,and wing feather structure in the barn owl (Tyto alba)

Feathers confer protection against biophysical agents and determine flying ability. The geometry and arrangement of the barbs, together with the keratin and pigments deposited in the feathers, determine the mechanical stability of the vane, and its stiffness and resistance to abrasive agents. In colour‐polymorphic species, individuals display alternative colour morphs, which can be associated with different foraging strategies. Each morph may therefore require specific flying abilities, and their feathers may be exposed to different abrasive agents. Feathers of differently coloured individuals may thus have a specific structure, and colour pigments may help resist abrasive agents and improve stiffness. We examined these predictions in the barn owl (Tyto alba), a species for which the ventral body side varies from white to dark reddish pheomelanic, and in the number and size of black spots located at the tip of the feathers. White and reddish birds show different foraging strategies, and the size of black feather spots is associated with several phenotypic attributes. We found that birds displaying a darker reddish coloration on the ventral body side deposit more melanin pigments in their remiges, which also have fewer barbs. This suggests that wear resistance increases with darkness, whereas feathers of lighter coloured birds may bend less easily. Accordingly, individuals displaying a lighter reddish coloration on the ventral body side, and those displaying larger black spots, displayed more black transverse bars on their remiges: as larger‐spotted individuals are heavier and longer‐winged birds also have more transverse bars, these bars may reduce feather bending when flying. We conclude that differently coloured individuals produce wing feathers of different strengths to adopt alternative behavioural and life history strategies. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 109 , 562–573.     

Coral reef flounders,Bothus lunatus,choose substrates on which they can achieve camouflage with their limited body pattern repertoire

Camouflage is a common tactic to avoid detection or recognition by predators and prey. Flounders have adaptive camouflage but a limited body pattern repertoire. We tested whether peacock flounders actively select or avoid certain substrates to more effectively use their limited camouflaging ability. We acquired and analyzed ten 30‐min videos of individual flounders on a coral reef in Bonaire, Dutch Caribbean. Using Manly's beta resource selection indices, we were able to confirm that peacock flounders at this location preferred to settle on neutral‐coloured substrates, such as sand and dead coral. Moreover, they avoided live coral, cyanobacteria, and sponges, which are often brightly coloured (e.g. yellow, orange, and purple). Quantitative analyses of photographs of settled flounders indicate that they use uniform and mottled camouflage patterns, and that the small‐to‐moderate spatial scale of their physiologically controlled light and dark skin components limits their camouflage capabilities to substrates with similar colour and spatial frequencies. These fishes changed their body pattern very fast. We did not observe disruptive body patterns, which are generally characterized by large‐scale skin components and higher contrast. The results suggest that flounders are using visual information to actively choose substrates on which they can achieve general background resemblance. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, 114 , 629–638.     

High fitness costs of climate change‐induced camouflage mismatch

Anthropogenic climate change has created myriad stressors that threaten to cause local extinctions if wild populations fail to adapt to novel conditions. We studied individual and population‐level fitness costs of a climate change‐induced stressor: camouflage mismatch in seasonally colour molting species confronting decreasing snow cover duration. Based on field measurements of radiocollared snowshoe hares, we found strong selection on coat colour molt phenology, such that animals mismatched with the colour of their background experienced weekly survival decreases up to 7%. In the absence of adaptive response, we show that these mortality costs would result in strong population‐level declines by the end of the century. However, natural selection acting on wide individual variation in molt phenology might enable evolutionary adaptation to camouflage mismatch. We conclude that evolutionary rescue will be critical for hares and other colour molting species to keep up with climate change.     

Adaptive body patterning,three‐dimensional skin morphology and camouflage measures of the slender filefish Monacanthus tuckeri on a Caribbean coral reef

The slender filefish is a master of adaptive camouflage and can change its appearance within 1–3 s. Videos and photographs of this animal's cryptic body patterning and behavior were collected in situ under natural light on a Caribbean coral reef. We present an ethogram of body patterning components that includes large‐ and small‐scale spots, stripes and bars that confer a variety of cryptic patterns amidst a range of complex backgrounds. Field images were analyzed to investigate two aspects of camouflage effectiveness: (1) the degree of colour resemblance between animals and their nearby visual stimuli; and (2) the visibility of each fish's actual body outline vs. its illusory outline. Most animals more closely matched the colour of nearby visual stimuli than that of the surrounding background. Three‐dimensional dermal flaps complement the melanophore skin patterns by enhancing the complexity of the fish's physical skin texture to disguise its actual body shape, and the morphology of these structures was studied. The results suggest that the body patterns, skin texture, postures and swimming orientations putatively hinder both the detection and recognition of the fish by potential visual predators. Overall, the rapid speed of change of multiple patterns, colour blending with nearby backgrounds, and the physically complicated edge produced by dermal flaps effectively camouflage this animal among soft corals and macroalgae in the Caribbean Sea.     

Bimodal colour pattern of individual Pinus halepensis Mill. seeds: a new type of crypsis

Variation in seed traits is a well‐known phenomenon affecting plant ecology and evolution. Here we describe, for the first time, a bimodal colour pattern of individual seeds, proposing an adaptive explanation, using Pinus halepensis as a model. Pinus halepensis disperses its seeds either by wind on hot dry days, from regular cones, or after fires, mainly from serotinous cones. Post‐dispersal seeds are exposed to strong predation by passerine birds, making crypsis important for seed survival. Individual seeds from non‐serotinous cones have a bimodal colour pattern: one side is light brown and the other black, exposing only one colour when lying on the ground. Serotinous cones from most trees have seeds with similar bimodal colour patterns, whereas seeds from serotinous cones of some trees are light brown on both sides. The dark side provides the seed with better crypsis on dark soils, whereas the light‐brown side is better adapted to light‐coloured soils, and mainly to light‐grey ash‐covered soil, which is the natural post‐fire regeneration niche of P. halepensis. The relative reflection curves of the black and brown seed colours differ, and their calculated relative chromatic distance is 5: meaning that seed‐predating passerine birds see them differently, and probably prefer seeds that present a higher contrast against the soil background. We propose that such a bimodal colour pattern of individual seeds is probably an overlooked general phenomenon mainly linked to seed dispersal in post‐fire and other heterogeneous environments. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 109 , 271–278.     

Cuttlefish camouflage: a quantitative study of patterning

To investigate camouflage design, we compared the responses of two species of cuttlefish ( Sepia officinalis and Sepia pharaonis ) with controlled but naturalistic backgrounds, consisting of mixtures of 1-mm and 9-mm diameter coloured pebbles. Quantitative analysis of image data using methods adapted from functional imaging research found differences in how the two species camouflage themselves. Whereas S. officinalis switches from background resemblance to a disruptive pattern as it moves from a fine to a coarsely patterned background particle, S. pharaonis blends the two types of pattern. We suggest that the differences may arise because S. pharaonis needs to produce camouflage that is effective when viewed over a relatively wide range of distances.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 92 , 335–345.     

Geographical and morphological variation within and between colour phases in Coris julis (L. 1758), a protogynous marine fish

The possible differences between sexes in patterns of morphological variation in geographical space have been explored only in gonochorist freshwater species. We explored patterns of body shape variation in geographical space in a marine sequential hermaphrodite species, Coris julis (L. 1758), analyzing variation both within and between colour phases, through the use of geometric morphometrics and spatially‐explicit statistical analyses. We also tested for the association of body shape with two environmental variables: temperature and chlorophyll a concentration, as obtained from time‐series of satellite‐derived data. Both colour phases showed a significant morphological variation in geographical space and patterns of variation divergent between phases. Although the morphological variation was qualitatively similar, individuals in the initial colour phase showed a more marked variation than individuals in the terminal phase. Body shape showed a weak but significant correlation with environmental variables, which was more pronounced in primary specimens. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 104 , 148–162.     

The ecology of multiple colour defences

Individuals of many species are considered to rely on a single type of external appearance to escape predation but there are many notable exceptions. To develop an ecological framework to explain why some individuals employ different colour patterns as part of their defensive repertoire, we collate examples of colour change that are associated with living in different environments and microhabitats, examples of age-related colour change, colour defences tailored to different predators, and startle displays, where hidden conspicuous colour patterns are suddenly revealed. The over-arching commonality to all these examples is that the use of more than one defense-related external appearance is associated with a spatial or temporal change in predation risk. For example, coarse scale temporal changes in an animal’s background frequently select for gradual colour changes, while fine-scale spatial heterogeneity selects for more rapid colour changes and we provide a graphical framework for this. Irrespective of the mechanisms underlying colour change, using more than one colour defence appears driven by variation in predation risk rather than by idiosyncratic abilities to alter external appearances as is commonly believed, although physiological and energetic factors will play some role.     

Body‐colour variation in an orb‐web spider and its effect on predation success

Animal body coloration serves several functions such as thermoregulation, camouflage, aposematism, and intraspecific communication. In some orb‐web spiders, bright and conspicuous body colours are used to attract prey. On the other hand, there are other species whose body colour does not attract prey. Using a spider species showing individual body‐colour variation, the present study aimed to determine whether or not the variation in body colour shows a correlation with predation rates. We studied the orb‐web spider (Cyclosa argenteoalba) using both field observations and T‐maze experiments, in which the prey were exposed to differently coloured spiders. Cyclosa argenteoalba has silver‐ and black‐coloured areas on its dorsal abdomen, with the ratio of these two colours varying continuously among individuals. The bright and conspicuous silver area reflects ultraviolet light. Results of both field observations and colour choice experiments using Drosophila flies as prey showed that darker spiders have a greater chance of capturing prey than silver spiders. This indicates that body‐colour variation affects predation success among individuals and that the bright silver colour does not function to attract prey in C. argenteoalba.     

Physiological colour change in the Moorish gecko,Tarentola mauritanica (Squamata: Gekkonidae): effects of background,light, and temperature

Colour has many different functions in animals, such as an involvement in thermoregulation, crypsis, and social interactions. Species capable of physiological colour change may alter their coloration in response to ecological conditions. The Moorish gecko, Tarentola mauritanica, is capable of actively changing its body coloration. In the present study, we investigated colour change in this gecko as a function of background, temperature, and light. Our results demonstrate that the Moorish gecko indeed changes its dorsal colour in response to changes in environmental conditions. By contrast to several other reptilian species, this rapid colour change does not appear to be associated with thermoregulation. Background matching, however, did appear to be a prominent function, although illumination appears to be an essential trigger. Future research should concentrate on individual variation and its effectiveness with respect to antipredatory mechanisms. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ?? , ??–??.     

Fear of the dark: substrate preference in Amazonian tadpoles

acta ethologica - Due to the importance of camouflage to avoid detection by predators, predation pressure can cause coupled evolution of skin colour and preference for substrate colour. Individuals...     

Nest covering in plovers: How modifying the visual environment influences egg camouflage

Camouflage is one of the most widespread antipredator defences, and its mechanistic basis has attracted considerable interest in recent years. The effectiveness of camouflage depends on the interaction between an animal's appearance and its background. Concealment can therefore be improved by changes to an animal's own appearance, by behaviorally selecting an optimal background, or by modifying the background to better match the animal's own appearance. Research to date has largely focussed on the first of these mechanisms, whereas there has been little work on the second and almost none on the third. Even though a number of animal species may potentially modify their environment to improve individual‐specific camouflage, this has rarely if ever been quantitatively investigated, or its adaptive value tested. Kittlitz's plovers (Charadrius pecuarius) use material (stones and vegetation) to cover their nests when predators approach, providing concealment that is independent of the inflexible appearance of the adult or eggs, and that can be adjusted to suit the local surrounding background. We used digital imaging and predator vision modeling to investigate the camouflage properties of covered nests, and whether their camouflage affected their survival. The plovers' nest‐covering materials were consistent with a trade‐off between selecting materials that matched the color of the eggs, while resulting in poorer nest pattern and contrast matching to the nest surroundings. Alternatively, the systematic use of materials with high‐contrast and small‐pattern grain sizes could reflect a deliberate disruptive coloration strategy, whereby high‐contrast material breaks up the telltale outline of the clutch. No camouflage variables predicted nest survival. Our study highlights the potential for camouflage to be enhanced by background modification. This provides a flexible system for modifying an animal's conspicuousness, to which the main limitation may be the available materials rather than the animal's appearance.