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AbstractIntraspecific variation in camouflage is common in animals. Sexual dimorphism in camouflage is less common and, where observed, attributed to trade-offs between natural selection for predator avoidance and sexual selection for conspicuous mating signals. Here we report on variation in putatively cryptic ventral hindwing patterns in the American snout butterfly, Libytheana carinenta. We use field surveys and crowdsourced data to characterize three morphs. One is found in both sexes, one is male specific, and one is female specific. The sex-specific morphs constitute a sexually dimorphic set whose frequencies change together in time. Field surveys indicate that butterflies in southern Arizona transition from midsummer dominance of the sexually monomorphic pattern to early-fall dominance of the sexually dimorphic set. Crowdsourced data indicate that the sexually dimorphic set dominates in early spring, transitioning later into a mixture of morphs dominated by the monomorphic pattern, with the dimorphic set rising in frequency again in late fall. We discuss this unique pattern of camouflage variation with respect to contemporary theory on animal coloration.
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Mariposas Diurnas , Pigmentación , Estaciones del Año , Alas de Animales , Animales , Mariposas Diurnas/anatomía & histología , Mariposas Diurnas/fisiología , Alas de Animales/anatomía & histología , Masculino , Femenino , Arizona , Caracteres Sexuales , Mimetismo BiológicoRESUMEN
The selective factors that shape phenotypic diversity in prey communities with aposematic animals are diverse and coincide with similar diversity in the strength of underlying secondary defences. However, quantitative assessments of colour pattern variation and the strength of chemical defences in assemblages of aposematic species are lacking. We quantified colour pattern diversity using quantitative colour pattern analysis (QCPA) in 13 dorid nudibranch species (Infraorder: Doridoidei) that varied in the strength of their chemical defences. We accounted for the physiological properties of a potential predator's visual system (a triggerfish, Rhinecanthus aculeatus) and modelled the appearance of nudibranchs from multiple viewing distances (2 and 10 cm). We identified distinct colour pattern properties associated with the presence and strength of chemical defences. Specifically, increases in chemical defences indicated increases in colour pattern boldness (i.e. visual contrast elicited via either or potentially coinciding chromatic, achromatic and/or spatial contrast). Colour patterns were also less variable among species with chemical defences when compared to undefended species. Our results indicate correlations between secondary defences and diverse, bold colouration while showing that chemical defences coincide with decreased colour pattern variability among species. Our study suggests that complex spatiochromatic properties of colour patterns perceived by potential predators can be used to make inferences on the presence and strength of chemical defences.
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Color , Gastrópodos , Conducta Predatoria , Animales , Gastrópodos/fisiología , Pigmentación , Mimetismo BiológicoRESUMEN
Conspicuous colours have fascinated biologists for centuries, leading to research on the evolution and functional significance of colour traits. In many cases, research suggests that conspicuous colours are adaptive and serve a function in sexual or aposematic signalling. In other cases, a lack of evidence for the adaptive value of conspicuous colours garners interest from biologists, such as when organisms that live underground and are rarely exposed to the surface are nevertheless colourful. Here, we use phylogenetic comparative methods to investigate colour evolution throughout freshwater crayfishes that vary in burrowing ability. Within the taxa we analysed, conspicuous colours have evolved independently over 50 times, and these colours are more common in semi-terrestrial crayfishes that construct extensive burrows. The intuitive but not evolutionarily justified assumption when presented with these results is to assume that these colours are adaptive. But contrary to this intuition, we discuss the hypothesis that colouration in crayfish is neutral. Supporting these ideas, the small population sizes and reduced gene flow within semi-terrestrial burrowing crayfishes may lead to the fixation of colour-phenotype mutations. Overall, our work brings into question the traditional view of animal colouration as a perfectly adapted phenotype.
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Astacoidea , Evolución Biológica , Pigmentación , Animales , Astacoidea/fisiología , Astacoidea/genética , Color , Filogenia , FenotipoRESUMEN
The persistence of non-neutral trait polymorphism is enigmatic because stabilizing selection is expected to deplete variation. In cryptically coloured prey, negative frequency-dependent selection due to search image formation by predators has been proposed to favour rare variants, promoting polymorphism. However, in a heterogeneous environment, locally varying disruptive selection favours patch type-specific optima, resulting in spatial segregation of colour variants. Here, we address whether negative frequency-dependent selection can overcome selection posed by habitat heterogeneity to promote local polymorphism using an individual-based model. In addition, we compare how prey and predator mobility may modify the outcome. Our model revealed that frequency-dependent predation could strongly promote local prey polymorphism, but only when differences between morphs in patch-specific fitness were small. The effect of frequency-dependent predation depended on the predator adjustment of search image and was hampered by the prey population structure. Gene flow due to prey movement counteracted local selection, promoted local polymorphism to some extent, and relaxed the conditions for polymorphism due to frequency-dependent predation. Importantly, abrupt spatial changes in morph frequencies decreased the probability that mobile frequency-dependent predators could maintain local prey polymorphism. Overall, our study suggests that in a spatially heterogeneous environment, negative frequency-dependent selection may help maintain local polymorphism but only under a limited range of conditions.
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Flujo Génico , Polimorfismo Genético , Animales , Color , Fenotipo , Conducta PredatoriaRESUMEN
AbstractAnimal coloration serves many biological functions and must therefore balance potentially competing selective pressures. For example, many animals have camouflage in which coloration matches the visual background that predators scan for prey. However, different colors reflect different amounts of solar radiation and may therefore have thermoregulatory implications as well. In this study, we examined geographic variation in dorsal patterning, coloration, and solar reflectance among horned larks (Eremophila alpestris) of the western United States. We found that plumage brightness was positively associated with soil granularity, aridity, and temperature. Plumage redness-both in terms of saturation (i.e., chroma) and hue-was positively associated with soil redness and temperature, while plumage patterning was positively associated with soil granularity. Together, these plumage-environment associations support both background matching and Gloger's rule, a widespread ecogeographic pattern in animal coloration. We also constructed thermoregulatory models that estimated cooling benefits provided by solar reflectance profiles of the dorsal plumage of each specimen based on the collection site. We found increased cooling benefits in hotter, more arid environments. Finally, cooling benefits were positively associated with residual brightness, such that individuals that were brighter than expected based on environmental conditions also had higher cooling benefits, suggesting a trade-off between camouflage and thermoregulation. Together, these data suggest that natural selection has balanced camouflage and thermoregulation in horned larks, and they illustrate how multiple competing evolutionary pressures may interact to shape geographic variation in adaptive phenotypes.
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Passeriformes , Pájaros Cantores , Animales , Regulación de la Temperatura Corporal , Evolución Biológica , Suelo , PigmentaciónRESUMEN
Prey animals typically try to avoid being detected and/or advertise to would-be predators that they should be avoided. Both anti-predator strategies primarily rely on colour to succeed, but the specific patterning used is also important. While the role of patterning in camouflage is relatively clear, the design features of aposematic patterns are less well understood. Here, we use a comparative approach to investigate how pattern use varies across a phylogeny of 268 species of cryptic and aposematic butterfly larvae, which also vary in social behaviour. We find that longitudinal stripes are used more frequently by cryptic larvae, and that patterns putatively linked to crypsis are more likely to be used by solitary larvae. By contrast, aposematic larvae are more likely to use horizontal bands and spots, but we find no differences in the use of individual pattern elements between solitary and gregarious aposematic species. However, solitary aposematic larvae are more likely to display multiple pattern elements, whereas those with no pattern are more likely to be gregarious. Our study advances our understanding of how pattern variation, coloration and social behaviour covary across lepidopteran larvae, and highlights new questions about how patterning affects larval detectability and predator responses to aposematic prey.
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Mariposas Diurnas , Animales , Larva/fisiología , Filogenia , Conducta Social , Conducta Predatoria/fisiologíaRESUMEN
Aposematic signals visually advertise underlying anti-predatory defences in many species. They should be detectable (e.g. contrasting against the background) and bold (e.g. using internal pattern contrast) to enhance predator recognition, learning and memorization. However, the signalling function of aposematic colour patterns may be distance-dependent: signals may be undetectable from a distance to reduce increased attacks from naïve predators but bold when viewed up close. Using quantitative colour pattern analysis, we quantified the chromatic and achromatic detectability and boldness of colour patterns in 13 nudibranch species with variable strength of chemical defences in terms of unpalatability and toxicity, approximating the visual perception of a triggerfish (Rhinecanthus aculeatus) across a predation sequence (detection to subjugation). When viewed from an ecologically relevant distance of 30 cm, there were no differences in detectability and boldness between well-defended and undefended species. However, when viewed at closer distances (less than 30 cm), well-defended species were more detectable and bolder than undefended species. As distance increased, detectability decreased more significantly than boldness for defended species. For undefended species, boldness and detectability remained comparatively consistent, regardless of viewing distance. We provide evidence for distance-dependent signalling in aposematic nudibranchs and highlight the importance of distinguishing signal detectability from boldness in studies of aposematism.
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Evolución Biológica , Gastrópodos , Animales , Percepción Visual , Aprendizaje , Conducta PredatoriaRESUMEN
Countershading is a gradient of colouration in which the illuminated dorsal surfaces are darker than the unilluminated ventral surface. It is widespread in the animal kingdom and endows the body with a more uniform colour to decrease the chance of detection by predators. Although recent empirical studies support the theory of survival advantage conferred by countershading, this camouflage strategy has evolved only in some of the cryptic animals, and our understanding of the factors that affect the evolution of countershading is limited. This study examined the association between body size and countershading using lepidopteran larvae (caterpillars) as a model system. Specifically, we predicted that countershading may have selectively evolved in large-sized species among cryptic caterpillars if (1) large size constrains camouflage which facilitates the evolution of a trait reinforcing their crypsis and (2) the survival advantage of countershading is size-dependent. Phylogenetic analyses of four different lepidopteran families (Saturniidae, Sphingidae, Erebidae, and Geometridae) suggest equivocal results: countershading was more likely to be found in larger species in Saturniidae but not in the other families. The field predation experiment assuming avian predators did not support size-dependent predation in countershaded prey. Collectively, we found only weak evidence that body size is associated with countershading in caterpillars. Our results suggest that body size is not a universal factor that has shaped the interspecific variation in countershading observed in caterpillars.
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Pigmentación , Conducta Predatoria , Animales , Filogenia , Tamaño Corporal , LarvaRESUMEN
Disruptive markings are common in animal patterns and can provide camouflage benefits by concealing the body's true edges and/or by breaking the surface of the body into multiple depth planes. Disruptive patterns that are accentuated by high contrast borders are most likely to provide false depth cues to enhance camouflage, but studies to date have used visual detection models or humans as predators. We presented three-dimensional-printed moth-like targets to wild bird predators to determine whether: (1) three-dimensional prey with disrupted body surfaces have higher survival than three-dimensional prey with continuous surfaces, (2) two-dimensional prey with disruptive patterns or enhanced edge markings have higher survival than non-patterned two-dimensional prey. We found a survival benefit for three-dimensional prey with disrupted surfaces, and a significant effect of mean wing luminance. There was no evidence that false depth cues provided the same protective benefits as physical surface disruption in three-dimensional prey, perhaps because our treatments did not mimic the complexity of patterns found in natural animal markings. Our findings indicate that disruption of surface continuity is an important strategy for concealing a three-dimensional body shape.
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Mariposas Nocturnas , Pigmentación , Humanos , Animales , Conducta Predatoria , Aves , Señales (Psicología)RESUMEN
Coexistence with related species poses evolutionary challenges to which populations may react in diverse ways. When exposed to similar environments, sympatric populations of two species may adopt similar phenotypic trait values. However, selection may also favour trait divergence as a way to reduce competition for resources or mates. The characteristics of external body parts, such as coloration and external morphology, are involved to varying degrees in intraspecific signalling as well as in the adaptation to the environment and consequently may be diversely affected by interspecific interactions in sympatry. Here, we studied the effect of sympatry on various colour and morphological traits in males and females of two related newt species Lissotriton helveticus and L. vulgaris. Importantly, we did not only estimate how raw trait differences between species respond to sympatry, but also the marginal responses after controlling for environmental variation. We found that dorsal and caudal coloration converged in sympatry, likely reflecting their role in adaptation to local environments, especially concealment from predators. In contrast, aspects of male and female ventral coloration, which harbours sexual signals in both species, diverged in sympatry. This divergence may reduce opportunities for interspecific sexual interactions and the associated loss of energy, suggesting reproductive character displacement (RCD). Our study emphasizes the contrasting patterns of traits involved in different functions and calls for the need to consider this diversity in evolutionary studies.
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Evolución Biológica , Salamandridae , Animales , Femenino , Masculino , Salamandridae/genética , SimpatríaRESUMEN
To counterbalance demands of different selective pressures, many species possess morphological, physiological and behavioral specializations that increase survival in their environments. Predation is one such pressure that can elicit multiple adaptive responses, and the effectiveness of antipredator behaviors likely vary both by environment and individual across time. Chameleons use multiple antipredator strategies, many of which vary with body size and habitat type. Although their unique morphological and physiological traits produce relatively slow locomotion, which is poorly suited for fleeing, chameleons can also use crypsis or aggression to avoid predation. To examine the functional basis for variable antipredator behavioral responses, we subjected chameleons to a series of mock predation trials and determined how often individuals adopted each antipredator strategy, and then quantified the performance capacities underlying each strategy. In particular, we measured bite force as a determinant for aggression, sprint velocity for fleeing, and degree of color change for crypsis. We found that aggression was predicted by traits associated with higher absolute and relative bite force, as well as habitat type; fleeing was predicted by higher normalized sprint velocity and habitat type; and crypsis was predicted by habitat type, color change capacity in bird color space and the interaction between the two. These results illustrate the importance of considering both functional capacity and environmental context in antipredator behavior decision-making.
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Lagartos , Animales , Fuerza de la Mordida , Tamaño Corporal , Ecosistema , Humanos , Lagartos/fisiología , Conducta Predatoria/fisiologíaRESUMEN
Background matching is perhaps the most ubiquitous form of defensive camouflage in the animal kingdom, an adaptive strategy that relies on the visual resemblance between a prey organism and its background to promote concealment from predators. The importance of background matching has been acknowledged for over a century, yet despite its renown and apparent pervasiveness, few studies exist that have objectively quantified its occurrence and tested the functional significance of background matching in a specific animal study system. The North Island lichen moth Declana atronivea presents a fascinating system to investigate such anti-predator coloration. This species possesses high contrast black and white forewings that appear to resemble lichen. Here we assessed the contribution of background matching to the antipredator defence of D. atronivea using field predation experiments with realistic models. We found that D. atronivea coloration confers a significant survival advantage against native avian predators when on lichen backgrounds compared to bark backgrounds, with an intermediate level of predation occurring when models were near, but not on lichen. This suggests that D. atronivea wing patterns are an adaptation for background matching. We subsequently used calibrated digital photography, avian vision modelling and image analysis techniques to objectively quantify the degree of background matching exhibited by D. atronivea and assessed the contribution of different visual elements (colour, luminance and pattern) to camouflage in this species. Only the pattern elements of D. atronivea presented a close match to that of the lichen backgrounds, with both chromatic and achromatic cues found to be poor predictors of background matching in this species. This study is one of the first to integrate vision modelling, quantitative image analysis and field predation experiments using realistic models to objectively quantify the level and functional significance of background matching in a real species, and presents an ideal system for further investigating the interrelation between multiple mechanisms of camouflage.
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Líquenes , Mariposas Nocturnas , AnimalesRESUMEN
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.
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Opsinas , Opsinas de Bastones , Luz , Opsinas/genética , Células Fotorreceptoras , Retina , Opsinas de Bastones/genética , Pigmentación de la Piel/genéticaRESUMEN
Optimal camouflage can, in principle, be relatively easily achieved in simple, homogeneous, environments where backgrounds always have the same colour, brightness and patterning. Natural environments are, however, rarely homogenous, and species often find themselves viewed against varied backgrounds where the task of concealment is more challenging. One result of variable backgrounds is the evolution of intraspecific phenotypic variation which may either be generalized, with multiple similarly cryptic patterns, or specialized, with each discrete colour form maximizing concealment against a single component of the background. We investigated the role of phenotypic variation in a highly variable population of the Neotropical toad Rhinella margaritifera using visual modelling and a computer-based detection task. We found that phenotypic variation was not divided into discrete colour morphs, and all toads were well camouflaged against the forest floor. However, although the whole population may appear to consist of random samples from the background, the toads were a particularly close match to the leaf litter, suggesting that they masquerade as dead leaves, which are themselves variable. Furthermore, rather than each colour form being equally effective against a single background, each toad was specialized towards its own particular local surroundings, as suggested by a specialist strategy. Taken together, these data highlight the importance of background matching to a nominally masquerading species, as well as how habitat heterogeneity at multiple spatial scales may affect the evolution of camouflage and phenotypic variation.
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Ecosistema , Pigmentación , Color , Ambiente , Hojas de la PlantaRESUMEN
Obligate brood parasitism is associated with huge reproduction costs, forcing hosts to evolve various anti-parasitic strategies against brood parasites, among which egg recognition and rejection is the most effective defense strategy. According to the crypsis hypothesis, non-mimetic yet cryptic eggs in a nest can also deceive their hosts and eventually be accepted. To validate this hypothesis, we conducted field experiments on Oriental reed warblers (Acrocephalus orientalis), a common host for common cuckoos (Cuculus canorus). We firstly tested the egg recognition and rejection abilities of Oriental reed warblers, using black and white model eggs in natural nests. Then we designed a comparison test where the cryptic effects of the two groups of experimental eggs were different. We manipulated the nest lining color and added relatively cryptic and bright model eggs to test warblers' rejection behaviors against cryptic and bright foreign eggs. The results showed that warblers have strong egg recognition and rejection abilities. There is a significant tendency for warblers to prefer to peck and reject relatively distinguishable foreign eggs, which supports the crypsis hypothesis. These findings indicate that even in the host-parasite system of open nests, parasitic eggs that are cryptic enough are prevented from being discovered and rejected by the host, and thus obtain the possibility of successful parasitism.
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Passeriformes , Pájaros Cantores , Animales , Comportamiento de Nidificación , Reconocimiento en Psicología , ReproducciónRESUMEN
Pathogenic microorganisms entail enormous problems for humans, livestock, and crop plants. A better understanding of the different infection strategies of the pathogens enables us to derive optimal treatments to mitigate infectious diseases or develop vaccinations preventing the occurrence of infections altogether. In this review, we highlight the current trends in mathematical modeling approaches and related methods used for understanding host-pathogen interactions. Since these interactions can be described on vastly different temporal and spatial scales as well as abstraction levels, a variety of computational and mathematical approaches are presented. Particular emphasis is placed on dynamic optimization, game theory, and spatial modeling, as they are attracting more and more interest in systems biology. Furthermore, these approaches are often combined to illuminate the complexities of the interactions between pathogens and their host. We also discuss the phenomena of molecular mimicry and crypsis as well as the interplay between defense and counter defense. As a conclusion, we provide an overview of method characteristics to assist non-experts in their decision for modeling approaches and interdisciplinary understanding.
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Interacciones Huésped-Patógeno/fisiología , Animales , Simulación por Computador , Humanos , Modelos Teóricos , Biología de Sistemas/métodosRESUMEN
BACKGROUND: Evolutionary transitions in temporal niche necessitates specialized morphology, physiology, and behaviors. Diurnal, heliothermic squamates (lizards and snakes) that bask require protection from ultraviolet radiation (UV) that can damage internal organs such as the brain, viscera, and gonads. Many smaller squamates have accomplished this protection by hyperpigmentation of the peritoneum and subcutaneous dorsum. Typically, nocturnal species do not require these protections from ultraviolet light. However, some nocturnal species that exhibit extreme crypsis may be exposed to sunlight and UV and require some means of mediating that damage. One such species is Gekko (Ptychozoon) kuhli, a nocturnal, arboreal gecko that uses extreme crypsis to blend in with tree bark. Hiding motionless on tree trunks leaves geckos exposed to sunlight during the day. Thus, we predict that G. kuhli will have independently evolved a hyperpigmented phenotype. To investigate this hypothesized association between temporal niche, behavior, and morphology, we characterized adult subcutaneous pigment for eight gecko species and embryonic pigment accumulation for a subset of four of these species, exhibiting diverse temporal niche and thermoregulatory behaviors. We predicted that nocturnal/potentially-heliothermic G. kuhli would exhibit hyperpigmentation of internal structures like that of diurnal/heliothermic geckos. We further predicted that embryonic pigment accumulation of G. kuhli would resemble that of diurnal/heliothermic as opposed to nocturnal/thigmothermic geckos. RESULTS: We found that temporal niche and thermoregulatory behavior predicted the degree of subcutaneous pigment in the eight gecko species examined. We demonstrate that G. kuhli accumulates pigment extremely early in embryonic development, unlike a diurnal/heliothermic gecko species, despite having a similar adult phenotype. CONCLUSIONS: The evolution of hyperpigmentation in G. kuhli is likely an adaptation to limit damage from occasional daytime UV exposure caused by crypsis-associated basking behavior. Gekko kuhli achieves its hyperpigmented phenotype through a derived developmental pattern, not seen in any other lizard species investigated to date, suggesting novel temporal differences in the migration and/or differentiation of reptilian neural crest derivatives.
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Lagartos/genética , Pigmentación , Adaptación Fisiológica/efectos de la radiación , Animales , Desarrollo Embrionario , Lagartos/fisiología , Fenotipo , Pigmentación/genética , Pigmentación/fisiología , Rayos UltravioletaRESUMEN
A three-dimensional body shape is problematic for camouflage because overhead lighting produces a luminance gradient across the body's surface. Countershading, a form of patterning where animals are darkest on their uppermost surface, is thought to counteract this luminance gradient and enhance concealment, but the mechanisms of protection remain unclear. Surprisingly, no study has examined how countershading alters prey contrast, or investigated how the presence of a dorsoventral luminance gradient affects detection under controlled viewing conditions. It has also been suggested that the direction of the dorsoventral luminance gradient (darkest or lightest on top) may interfere with predators' abilities to resolve prey's three-dimensional shape, yet this intriguing idea has never been tested. We used live fish predators (western rainbowfish, Melanotaenia australis) and computer-generated prey images to compare the detectability of uniformly pigmented (i.e. non-countershaded) prey with that of optimally countershaded prey of varying contrasts against the background. Optimally countershaded prey were difficult for predators to detect, and the probability and speed of detection depended on prey luminance contrast with the background. In comparison, non-countershaded prey were always highly detectable, even though their average luminance closely matched the luminance of the background. Our findings suggest that uniformly pigmented three-dimensional prey are highly conspicuous to predators because overhead lighting increases luminance contrast between different body parts or between the body and the background. We found no evidence for the notion that countershading interferes with predator perception of three-dimensional form.
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Pigmentación , Conducta Predatoria , Animales , Evolución Biológica , Cadena AlimentariaRESUMEN
Tarantulas paradoxically exhibit a diverse palette of vivid coloration despite their crepuscular to nocturnal habits. The evolutionary origin and maintenance of these colours remains mysterious. In this study, we reconstructed the ancestral states of both blue and green coloration in tarantula setae, and tested how these colours correlate with presence of stridulation, urtication and arboreality. Green coloration has probably evolved at least eight times, and blue coloration is probably an ancestral condition that appears to be lost more frequently than gained. While our results indicate that neither colour correlates with the presence of stridulation or urtication, the evolution of green coloration appears to depend upon the presence of arboreality, suggesting that it ptobably originated for and functions in crypsis through substrate matching among leaves. We also constructed a network of opsin homologues across tarantula transcriptomes. Despite their crepuscular tendencies, tarantulas express a considerable diversity of opsin genes-a finding that contradicts current consensus that tarantulas have poor colour vision on the basis of low opsin diversity. Overall, our findings raise the possibility that blue coloration could have ultimately evolved via sexual selection and perhaps proximately be used in mate choice or predation avoidance due to possible sex differences in mate-searching.
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Opsinas , Pigmentación , Arañas/fisiología , Animales , Color , Evolución Molecular , Conducta Predatoria , Opsinas de Bastones , Caracteres SexualesRESUMEN
Evading predators is a fundamental aspect of the ecology and evolution of all prey animals. In studying the influence of prey traits on predation risk, previous researchers have shown that crypsis reduces attack rates on resting prey, predation risk increases with increased prey activity, and rapid locomotion reduces attack rates and increases chances of surviving predator attacks. However, evidence for these conclusions is nearly always based on observations of selected species under artificial conditions. In nature, it remains unclear how defensive traits such as crypsis, activity levels and speed influence realized predation risk across species in a community. Whereas direct observations of predator-prey interactions in nature are rare, insight can be gained by quantifying bodily damage caused by failed predator attacks. We quantified how butterfly species traits affect predation risk in nature by determining how defensive traits correlate with wing damage caused by failed predation attempts, thereby providing the first robust multi-species comparative analysis of predator-induced bodily damage in wild animals. For 34 species of fruit-feeding butterflies in an African forest, we recorded wing damage and quantified crypsis, activity levels and flight speed. We then tested for correlations between damage parameters and species traits using comparative methods that account for measurement error. We detected considerable differences in the extent, location and symmetry of wing surface loss among species, with smaller differences between sexes. We found that males (but not females) of species that flew faster had substantially less wing surface loss. However, we found no correlation between cryptic coloration and symmetrical wing surface loss across species. In species in which males appeared to be more active than females, males had a lower proportion of symmetrical wing surface loss than females. Our results provide evidence that activity greatly influences the probability of attacks and that flying rapidly is effective for escaping pursuing predators in the wild, but we did not find evidence that cryptic species are less likely to be attacked while at rest.