Data from: Body size and evolution of motion dazzle coloration in lizards
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Camouflage
Summary Understanding the ecological function of an animal's pigmentation pattern is an intriguing research challenge. We used quantitative information on lizard foraging behaviour to search for movement correlates of patterns across taxa. We hypothesized that noticeable longitudinal stripes that enhance escape by motion dazzle are advantageous for mobile foragers that are highly detectable against the stationary background. Cryptic pigmentation patterns are beneficial for less‐mobile foragers that rely on camouflage to reduce predation. Using an extensive literature survey and phylogenetically controlled analyses, we found that striped lizards were substantially more mobile than lizards with cryptic patterns. The percentage of time spent moving was the major behavioural index responsible for this difference. We provide empirical support for the hypothesized association between lizard dorsal pigmentation patterns and foraging behaviour. Our simple yet comprehensive explanation may be relevant to many other taxa that present variation in body pigmentation patterns.
Camouflage
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Iguanidae
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Animals rely on different signaling patterns to communicate both within and between different species. Anolis is a diverse genus of small arboreal lizards that utilize a colorful expandable throat‐fan (or dewlap) for visual communication, in order to attract females and repel males. The environment the lizard lives in has influenced the coloring of these dewlaps in different species. Species that occupy shaded habitats tend to have yellow dewlaps while those that inhabit brighter, less shaded, habitats, tend to have red or orange dewlaps. Natural backgrounds are formed by green vegetation. Modelling these dewlap colors in a perceptual color space predicts that red is more visible against a green background than yellow, yet studies have shown that the majority of anoles have yellow dewlaps. However, quantal fluctuations under low lighting may result in a higher degree of receptor noise for some colors which can affect the discrimination of one color from another by changing the distance between them in perceptual color space. Modelling that takes receptor noise into account predicts that yellow colors, which reflect more photons, will be more visible than red in low light conditions, while red should be more visible in bright light where receptor noise is less. In this experiment, we used a color perception assay to test whether a red or yellow stimulus was more visible to the lizard under different light intensities against a green background, mimicking a dewlap appearing in a forested or open habitat. We flashed red, yellow, and green (control) stimuli against a green background. If the lizard detected a change, indicated by a swift head or eye movement towards the stimulus, a positive response was noted. We found that there was a significantly greater response to red stimuli in high light compared to low light. The visibility of yellow, however, did not change significantly with light intensity. In high light there was a greater response to red than to yellow, while in low light there was a greater response to yellow than to red. Our experiment confirmed the results predicted by the perceptual color space model when accounting for receptor noise. Since light intensity has a greater effect on the discriminability of red against green than yellow against green, this may account for the prevalence of yellow dewlaps in shaded habitats.
Anolis
Arboreal locomotion
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In polychromatic species, differences in conspicuousness among alternative color morphs may affect the costs and benefits relating to signal detectability by primary receivers and unintended observers. Using visual modeling, we studied the conspicuousness of the body coloration in a ventrally polychromatic population of common wall lizards (Podarcis muralis). This species shows a complex color pattern that combines brown dorsal coloration, long-wavelength–biased ventral coloration, and ventrolateral ultraviolet (UV)-blue patches that are used to signal male quality. Considering simultaneously the visual system of P. muralis and lizard predators, we quantified the chromatic and achromatic (intensity) contrasts of each body region viewed against natural backgrounds. We also quantified the internal contrast generated by pairs of adjacent color patches on the lizards' body surface. We found that, in some cases, color patches used for signaling are better tuned to conspecifics than to predators, and are more conspicuous in males than in females. The UV-blue patches viewed against the long-wavelength–biased ventral coloration provide the most conspicuous color combination, suggesting that ventral colors may act as an amplifier and highlighting the relevance of color pattern complexity. In contrast, the dorsal coloration is the most cryptic coloration. The color morphs differ in conspicuousness, probably resulting in differences in signal efficacy as well as in costs caused by predator detection. The orange morph is the most chromatically conspicuous to conspecifics and predators, whereas the white morph shows the least chromatic conspicuousness, suggesting that the trade-off between detection by primary receivers and predators may be morph-dependent.
Crypsis
Aposematism
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Aposematism
Gryllus bimaculatus
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Prey animals often protect themselves from visual hunting predators via their body coloration, which encompasses various visual effects. When a prey animal displays a certain color pattern on its body surface, its protective function and effect are largely dependent on how a predator would encounter and perceive the prey animal.Asian coral snakes of the genus Sinomicrurus,which are venomous, display black bands and stripes on their orange body coloration. The banded pattern has been characterized as an aposematic signal in the New World coral snakes, but the stripes generally occur in cryptic snakes. We investigated the function of this complex color pattern, which might be interpreted as aposematic and cryptic, in Sinomicrurus japonicusboettgeri.First, plasticine replica experiments were conducted to assess whether natural avian predators avoid the colorpattern of S.japonicus boettgeri;the results showed that they attacked the coral snake replicas and the control replicas with coloration similar to another prey snake, suggesting that the body coloration of S. japonicus boettgeri did not function aposematically in the wild. Second, we evaluated the chromatic contrast of the snake coloration with backgrounds from their natural habitats based on the avian predator visual systems. The body coloration of S. japonicus boettgeri showed the same, or lower, contrast levels with natural backgrounds than those of sympatric cryptic snakes, suggesting that the coloration was ineffective as an aposematic signal.These results imply that the body coloration of S. japonicus boettgeri would work as crypsis through background matching or disruptive camouflage rather than aposematism.
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Crypsis
Camouflage
Plasticine
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Conspicuous coloration is often used in combination with chemical defenses to deter predators from attacking. Experimental studies have shown that the avoidance inducing effect of conspicuous prey coloration increases with increasing size of pattern elements and with increasing body size. Here we use a comparative approach to test the prediction from these findings, namely that conspicuous coloration will evolve in tandem with body size. In our analysis, we use a previously published mitochondrial DNA‐based phylogeny and comparative analysis of independent contrasts to examine if evolutionary shifts in color pattern have been associated with evolutionary changes in body size in aposematic poison frogs (Anura: Dendrobatidae). Information on body size (snout to vent length) and coloration were obtained from the literature. Two different measures of conspicuousness were used, one based on rankings by human observers and the other based on computer analysis of digitized photographs. The results from comparative analyses using either measure of coloration indicated that avoidance inducing coloration and body size have evolved in concert in poison frogs. Results from reconstruction of character change further indicate that the correlated evolution of size and coloration has involved changes in both directions within each of the different clades of the phylogenetic tree. This finding is consistent with the hypothesis that selection imposed by visually guided predators has promoted the evolution of larger body size in species with conspicuous coloration, or enhanced evolution of conspicuous coloration in larger species.
Aposematism
Phylogenetic comparative methods
Camouflage
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Understanding the functions of animal coloration has been a long-standing question in evolutionary biology. For example, the widespread occurrence of striking longitudinal stripes and colourful tails in lizards begs for an explanation. Experiments have suggested that colourful tails can deflect attacks towards the tail (the 'deflection' hypothesis), which is sacrificable in most lizards, thereby increasing the chance of escape. Studies also suggest that in moving lizards, longitudinal body stripes can redirect predators' strikes towards the tail through the 'motion dazzle' effect. Despite these experimental studies, the ecological factors associated with the evolution of such striking colorations remain unexplored. Here, we investigated whether predictions from motion dazzle and attack deflection could explain the widespread occurrence of these striking marks using comparative methods and information on eco-physiological variables (caudal autotomy, diel activity, microhabitat and body temperature) potentially linked to their functioning. We found both longitudinal stripes and colourful tails are associated with diurnal activity and with the ability to lose the tail. Compared to stripeless species, striped species are more likely to be ground-dwelling and have higher body temperature, emphasizing the connection of stripes to mobility and rapid escape strategy. Colourful tails and stripes have evolved multiple times in a correlated fashion, suggesting that their functions may be linked. Overall, our results together with previous experimental studies support the notion that stripes and colourful tails in lizards may have protective functions based on deflective and motion dazzle effects.
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"Motion dazzle" patterns are a form of defensive coloration suggested to prevent successful capture during motion by causing predators to misjudge the direction or speed of prey movement. Several studies have found results supporting this idea but little is known about the factors that favor the evolution of these antipredator colorations. A recent experimental study has suggested that the longitudinal striped patterns on the body of lizards can redirect attacks to the tail via the motion dazzle effect. Using a virtual predation experiment with humans and a phylogenetic comparative analysis, we show that evolution of longitudinal striped coloration is associated with prey size. Experiments showed that longitudinal stripes located at the anterior reduced lethal attacks (i.e., attacks directed to the anterior and centre) but this benefit was greater for shorter prey. Our comparative analysis revealed a negative association between stripe occurrence and body length but no association between stripes and body width. Overall, our results suggest that the dazzle effect produced by stripes is more advantageous in shorter lizards than in longer ones and that the error induced by stripes might be distributed along the axis parallel to the prey trajectory. We discuss reasons why dazzle coloration could be associated with evolution of smaller body size in animals.
Phylogenetic comparative methods
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Hummingbird
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